Category Archives: Automotive

Know When You Need Brake Repairs

Brake repairs – critical? Of course! Your brakes keep your family safe. Brake repairs and parts for imports – expensive? You bet! Brake rotors for import cars, unlike domestics, are built with minimal thicknesses to save weight – meaning they can’t be “turned”; they must be replaced.

Brake rotors for imports are also more sensitive to warping from heat, and overheated brakes are the second most common cause of failure (first is wear-and-tear).

Save money on brake repairs and parts with these tips:

Use Your Eyes & Ears to Inspect Your Brakes
Visually inspect your brakes’ condition at least every six months. Here are some things to look for:

Brake Rotors (discs) should be inspected all the way around the surface and on both sides for any concentric scoring (grooves) or obvious defects. If defects are found, replace your rotors immediately. Any rotor discoloration may be a sign of overheating and an inspection by a brake repair professional is needed.

Brake Pads will normally match rotor scoring but should also be inspected for uneven wear, breakage or cracking on the friction surface. Again, if defects are found, replace the pads immediately. Many cars also have brake pad sensors to warn of pad wear. If your car uses sensors, replace these at the same time as your pads.

Brake Drums (if equipped) should also be inspected on a regular basis. Check for the same types of flaws as noted above. The drums should not have excessive grooves or have a deep “trough” dug into them where the shoes ride.

Brake Shoes (if equipped) should be worn evenly and have no rivets protruding to the friction surface.

Additional Troubleshooting: When inspecting brakes, check calipers, wheel cylinders, hoses and fittings for any hydraulic fluid leakage.

Inspect the master cylinder, reservoir and proportioning valve assemblies as well. Replace or rebuild as required.

A “spongy” brake pedal or one that’s gotten lower underfoot also needs looking into. It could be caused by sticking calipers, worn pads, low fluid or hydraulic system problems.

If you can’t “pump them up”, then you definitely have hydraulic problems that need work. If you always have to pump them up, at the very least your hydraulic fluid needs replacement.

To check brakes by sound, know how your brakes should sound and listen for out-of-the-ordinary noises.

Most cars have a slight brushing sound from the pads lightly touching the rotors. This is perfectly normal. Sounds to beware of include:

Squeaking may be caused by dust or dirt on the brakes, loose pads vibrating when applied or worn pads.

Rhythmic noise might mean you have a warped rotor. Instead of a solid squeaking noise, it pulsates. In extreme cases, the brake pedal will also pulsate underfoot.

Constant brake noise is never a good sound and any grinding noise spells real trouble!

Most importantly: As soon as any problem is noticed, get it repaired immediately. Delaying brake repairs is extremely dangerous.

Overstressed rotors and drums can break. Brakes may be too worn or damaged to stop your car in an emergency.

Even if you manage to avoid physical harm, the longer you delay fixing brake problems, the more you increase the cost of doing so.

Badly worn, warped or overheated rotors can damage wheel bearings and the complete wheel hub assembly. These parts often cost as much or more than the brakes themselves.

Even if you like doing your own work, every few years your brakes should be examined by a professional. Checking brakes for “run-out”, warping, wheel bearing play, proper proportioning balance, among others, are normally more involved than can be accomplished in your garage. This inspection can also uncover underlying problems that could eventually become costly or dangerous.

Important Things to Remember
Heed these tips and you’re on your way to ensuring your brakes won’t fail:

Tip #1: Keep the hydraulic reservoir at the proper level with the fluid type recommended by the car manufacturer. Never substitute or mix types of fluid. Remember also that hydraulic fluid absorbs water. Never use old hydraulic fluid – always use a fresh container.

Tip #2: Keep brakes clean by washing them off at the same time as your car. This keeps squeaky dust and dirt off the pads and makes brakes easier to inspect and work on.

Tip #3: Never spray, touch or drip any oil or lubricants on the brake friction surfaces. If this occurs, spray immediately with brake cleaner to remove completely.

Tip #4: There are no shortcuts or quick fixes to brake problems. They either function properly or they don’t. Know your brake system – how it should work, feel and sound – before it acts up so you’ll know when something’s wrong.

Tip #5: Most imports don’t have serviceable rotors. They must be replaced at the same time as the pads. The rotors cannot be “turned” to remove imperfections. There isn’t sufficient metal thickness to safely accomplish this.

Tip #6: Keep a repair log with receipts when any service is performed on your car. It helps when you need to check if your warranty is still in effect. More importantly, it’s a great gauge of performance and an indicator of other problems.

Tip #7: Whenever the pads are replaced, the hydraulic system must be bled to remove any air bubbles. Most specialists recommend changing the fluid with every pad replacement. If you’re unsure of the proper technique for bleeding the hydraulic system, don’t perform the job yourself. Seek help from a professional. ABS equipped cars should be bled only by professionals.

Tip #8: Most noises are usually related to your pads. However, whenever replacing pads, you should also replace the sensors and seriously consider replacing the rotors at the same time.

Tip #9: After installing new pads, remember to “set” them properly. This conditions them for maximum performance and prevents premature failure. Instructions for setting pads is usually provided in the package with your new pads.

Brake Parts Shopping List
When shopping for parts, remember two important things:

1. OEM/OES (original equipment manufactured/supplied) or equivalent pads and rotors are not always cheap. You do, however, get what you pay for. OE parts will give you the most trouble-free driving and peace of mind. And . . . isn’t that what’s most important?

2. Before requesting any brake parts for your import car, make sure you have the year, exact model designation, engine size and type, brake configuration, type of rotors (solid or vented), vehicle ID number (VIN) and production date. For Volvos, you’ll also need rotor diameter, caliper manufacturer and mount and shape of the pads.

Here is a list of parts you should consider when working on brake systems:

– Front Brake Rotors (Brake Discs) –
– Front Brake Pads –
– Rear Brake Rotors (Brake Discs) or Rear Brake Drums –
– Rear Brake Pads or Brake Shoes –
– Brake Sensors (front and/or rear, as applicable)
– Brake Calipers or Caliper Rebuild Kits –
– Wheel Cylinders –
– Hydraulic Hoses –
– Hose/Tube Fittings –
– Brake Master Cylinder –
– Power Booster –
– Reservoir & Grommets –
– Brake Proportioning Valve Assembly –
– Hydraulic & Brake Fluid –
– Brake Cleaner –
– Anti-Squeal Compound –
Don’t Forget:
Repair articles are added regularly.
Come back often to check for new maintenance topics.

These repair tips are designed only as a starting point.
Please seek the assistance of a professional mechanic
for all repair problems beyond your capabilities.

More Information About Diagnosing Returnless Fuel Injection Systems

Returnless systems are found on many late model cars and trucks. “Returnless” refers to the fact that these systems have the fuel pressure regulator inside the fuel tank. This eliminates the need for a fuel return line from the fuel injector rail on the engine to reroute excess fuel back to the fuel tank.

The first returnless fuel injection systems appeared back in 1993 on certain Chrysler V6 and V8 truck engines. By 1998, all Chrysler cars and light trucks had them. In 1996, Toyota introduced its first returnless system, followed by General Motors and Ford in 1999. Honda went “returnless” in 2001, and today you’ll find returnless fuel injection systems on almost all new vehicles.

returnless efi fuel injection system
In older return-type systems, the fuel pump delivers more fuel to the engine than it actually needs. The excess fuel is then routed back to the fuel tank through a pressure regulator and return line. This can increase the temperature of the fuel because of the heat it picks up while circulating through the fuel rail in the engine compartment. Eliminating the return line keeps fuel temperatures lower and more consistent for better fuel economy and emissions.

FUEL SYSTEM OPERATION

A returnless fuel injection system manages fuel pressure a little differently. Instead of using a spring-loaded vacuum diaphragm in the regulator to change fuel delivery when throttle opening and intake vacuum change, the regulator in a returnless system operates at a constant pressure. The older return-type systems need to vary fuel pressure to maintain the same pressure differential across the injectors when intake vacuum drops. When vacuum drops, the regulator increases pressure to compensate. But in a returnless system, this isn’t necessary because the line pressure is always the same.

So how does the system compensate for changes in engine load and vacuum? A returnless system uses the Powertrain Control Module (PCM) to regulate fuel delivery. A fuel pressure sensor mounted on the supply rail allows the PCM to monitor fuel pressure. When pressure in the supply rail drops as engine load or speed increase, the PCM compensates by increasing injector duration (on time) and/or the operating speed of the fuel pump.

Some systems (Ford, for example), vary the fuel pump’s output by changing the voltage supply to the fuel pump module. When more fuel is needed, pump speed is increased by increasing the pulse-width (on-time) of the pump’s voltage signal (pulse-width modulation).

WHY RETURNLESS FUEL INJECTION?

The older return-type fuel injection systems circulate a lot of fuel between the engine and tank. This keeps the fuel from getting too hot and boiling as it passes through the fuel rail on the engine (which can cause vapor lock and hard starting or stalling on hot days), but it also carries a lot of heat back to the fuel tank. Heat increases fuel vaporization inside the fuel tank, and puts more of a strain on the Evaporative Emissions (EVAP) control system.

The EVAP system’s job is to contain fuel vapors so they do not escape from the fuel tank and pollute the atmosphere. Fuel vapors pass through a vent hose to a charcoal-filled canister which temporarily traps and stores the vapors. Later, the vapors are purged from the canister via a control valve and routed into the engine while the vehicle is being driven.

The trouble is, EVAP systems have limited capacity and can only store so much fuel vapor. If the fuel is getting hot and vapor pressure is building up inside the tank, it can saturate the charcoal canister and overload the EVAP system’s ability to contain the vapors creating a potential emissions problem.

On newer vehicles with OBD II, the onboard diagnostic system is required to monitor the fuel system for vapor leaks. If the fuel in the tank gets too hot and builds up excessive pressure, it may cause a leak that will turn on the Malfunction Indicator Lamp (MIL) and set a diagnostic trouble code (DTC). What’s more, the U.S. Environmental Protection Agency tightened the limits for evaporative emissions, making it even more important to control fuel vapor pressure inside the tank.

With returnless systems, there is no return line and no circulation of fuel back to the fuel tank from the engine. Consequently, there is no heating of the fuel in the tank and no increase in fuel vapor pressure from driving the vehicle. This reduces the risk of excessive pressure build up inside the fuel tank, vapor leaks, and triggering an OBD II EVAP monitor DTC.

OTHER RETURNLESS FUEL INJECTION DIFFERENCES

Another difference is that returnless systems typically operate at a higher pressure than return-type systems. This is necessary to reduce the risk of fuel boiling and vapor lock in the injector supply rail during hot weather (since there is no recirculation of fuel from the engine back to the tank to keep the supply rail cool).

Returnless systems are very sensitive to fuel pressure, and if pressure is more than a few pounds out of specifications, it may be enough to cause a driveability or emissions problem.

Fuel pressure checks on returnless systems can be done in the usual way by attaching a gauge to the service valve fitting on the fuel supply rail, or you can hook up a scan tool and read the pressure value via the pressure sensor. Using a fuel pressure gauge to cross-check the accuracy of the electronic reading is a good way to check for a fuel pressure sensor that is out of calibration.

Remember, returnless systems are designed to operate at a constant pressure. A simple pressure check with a gauge or scan tool will tell you if the system is within specifications. Pressure should also be monitored with a scan tool while driving the vehicle to check for pressure loss under load.

If the operating pressure is out of range, the PCM will compensate by increasing or decreasing the short term fuel trim (STFT) and long term fuel trim (LTFT) values. As a rule, these numbers should usually be within plus or minus 10 points. If you see a higher or lower value on your scan tool, it may indicate a fuel mixture problem due to incorrect fuel pressure (bad fuel pressure sensor, bad fuel pressure regulator, a weak pump or low pump voltage), or an air leak, or dirty fuel injectors.

VOLUME JUST AS IMPORTANT AS PRESSURE

Fuel volume is just as important as pressure in all fuel injection systems. The pump has to push enough volume of fuel to keep up with the engine’s demands when it is under load, accelerating hard or running at wide open throttle. A weak pump may still produce enough pressure to be within specifications at idle, but may not deliver enough fuel at high rpm and load, causing fuel starvation, lean misfire and a loss of power.

As a rule, a “good” pump will deliver at least 750 ml (3/4 quart) of fuel in 30 seconds.

Sometime a low pressure or volume problem isn’t the fuel pump but a clogged filter, plugged fuel inlet filter sock, restricted fuel line or a faulty fuel pressure regulator. A low voltage supply to the fuel pump due to a wiring problem, low charging voltage or bad relay may also prevent the pump from operating at normal speed.

fuel pump assembly in fuel tank
A returnless fuel pump assembly contains the pump,
filter and regulator, plus the fuel level sensor and float.
Many applications also have a control module to regulate
pump speed and monitor the pump’s health.
RETURNLESS FUEL INJECTION TECH TIPS

* On returnless systems that use pulse-width modulation to vary the operating speed of the fuel pump, you should be able to read the value of the control signal on your scan tool. Look for a change in the number when engine speed/load change.

* The injector on the furthest end of the fuel rail(s) in a returnless system may be more prone to dirt contamination and clogging than injectors further upstream. Because there is no circulation of fuel back to the tank, the end of the fuel rail may become a sewer pipe and collect any debris that gets past the filter. The debris may clog the inlet screen in the injector and starve the injector causing that cylinder to run lean and misfire.

Cleaning the injectors on the engine may not help because the debris may remain trapped in the end of the fuel rail. It may be necessary to remove the injector(s) and fuel rail(s) for cleaning, or to replace the rail if the debris cannot be flushed out.

* For best performance, injector flow rates should not vary more than about 5% from one injector to the next on returnless systems. Injector flow rates can be measured and compared on a test bench. If this is not possible, and one or more injectors are clogged or dirty (and do not respond to cleaning), you should recommend replacing the entire set of injectors. Why? Because if you only replace the “problem” injector(s), the new one(s) will likely flow more fuel than the old ones (unless all have been cleaned and flow tested). This can create an overly rich condition in the cylinders with the new injectors, and cause a driveability or emissions problem you didn’t have before.

* Most fuel pump failures are caused by dirt or rust in the fuel tank. So it is very important to inspect the inside of the tank when a pump is replaced. If the tank is dirty, steam clean it. If a metal tank contains rust, replace it.

* When replacing a fuel filter, pour a little fuel through the filter inlet to “pre-wet” the filter element inside. This will reduce the risk of the filter element shredding loose paper fibers into the fuel system when the pump starts up and sends fuel at full force through the filter.

RETURNLESS FUEL INJECTION FUEL FILTERS

Another difference between some return-type and returnless fuel injection system is the location of the fuel filter. In most return-type systems, an in-line filter is positioned somewhere between the fuel tank and engine. The filter may be located under the vehicle in the fuel line that carries fuel from the tank to the engine, or in the engine compartment on the firewall or fuel rail. The filter typically has an OEM recommended replacement interval of 30,000 to 50,000 miles.

On some returnless systems, an in-line filter is also used. It may be located in the fuel line or engine compartment. On some hybrid “semi-returnless” systems, the filter is located outside the tank and routes fuel back to the tank through a third return port. But on some returnless systems, the fuel filter is located inside the fuel tank and is part of the fuel pump module or regulator.

What’s more, on some of these applications (Dodge Neon, for example), there is no OEM recommended replacement interval for the fuel filter! Others say to replace the filter “as needed.”

One reason for the extended filter life is because a returnless system pumps much less fuel through the filter. A typical return-type system may circulate up to 30 gallons of fuel per hour through the filter and return line. With a returnless system, the only fuel that passes through the filter is that which the engine burns. On a vehicle that gets 20 miles per gallon, that would only be about 3 gallons of fuel in an hour at 60 mph.

This doesn’t mean a filter with no OEM recommended replacement interval will last forever. It won’t. Eventually, the filter will become clogged and have to be replaced — and when it does the fuel tank will have to be drained and lowered to gain access to the filter and pump (unless the vehicle has an access panel under the back seat or in the trunk).

The life of the filter will depend on the cleanliness of the fuel that goes into the tank, driving conditions and corrosion inside the fuel tank (not an issue with plastic fuel tanks but can be with aging metal tanks).

If engine driveability or emissions problems indicate a restricted fuel filter, the fuel filter must be replaced regardless of mileage. It can also be replaced at any mileage interval for preventive maintenance, though in the case of an in-tank filter that could be an expensive and labor-intensive job.

On many of these returnless applications with in-tank filters, the fuel filter probably won’t be replaced until the pump fails — so it is very important to make sure you also install a new filter when you replace the pump.

The pump pickup “filter sock” should also be replaced when the pump is changed. And don’t forget to inspect the inside of the tank for dirt or rust!

How to Replace Fuel Filter

For reliable engine operation and fuel system performance, a clean fuel supply is absolutely essential. That’s why replacing the fuel filter is so important. The fuel filter is the fuel system’s primary line of defense against dirt, debris and small particles of rust that flake off the inside of the fuel tank. A mesh filter sock on the end of the fuel pickup tube inside the tank helps prevent the big pieces of dirt and rust from entering the fuel line, but it does not keep out smaller particles that can be so troublesome.

If not trapped by the filter, such contaminants can plug fuel metering orifices in a carburetor or prevent valves from seating. In fuel injected engines, fuel debris can clog the injector inlet screens and starve the injector for fuel. And if debris gets inside the injector, it can wear or jam the pintle valve and seat. With diesel engines, clean fuel is even more important because of the extremely close tolerances inside the injection pump.
Fuel filters on older carbureted engines typically trap particles as small as 70 to 100 microns in size (a micron is a millionth of a meter or 0.000039 inches). The diameter of a human hair is about 60 microns. By comparison, many filters for fuel injected engines trap particles as small as 10 to 40 microns in size. A good diesel fuel filter should trap particles as small as one micron in size!

FUEL FILTER MEDIA

The filter media may be treated paper, a blend of cellulose and synthetic fibers, glass fibers, sintered bronze, a ceramic material or even a fine nylon mesh. The barrier created by the filter media traps particles and prevents them from reaching the engine. Eventually the filter media becomes clogged with debris, which creates a restriction. If not replaced before it becomes plugged, it can cause major driveability problems (such as hard starting, lack of high speed power and/or stalling).

FUEL FILTER LOCATION

There are two basic types of fuel filters: “inline” filters that are mounted in the fuel line somewhere between the fuel tank and carburetor or fuel rail (EFI), and “internal” filters such as those that fit inside the carburetor fuel inlet on older vehicles.

On most fuel injected vehicles, the fuel filter will be found under the vehicle in the fuel line from the fuel tank to the engine, or on the firewall in the engine compartment. There are also some fuel filters on “returnless” EFI systems (Dodge Ram trucks and other late model Chrysler vehicles) that are located on top of the fuel tank and are part of the fuel pressure regulator assembly. Refer to your owner’s manual for the exact location of the filter.

fuel filter
An inline fuel filter located in the engine compartment.
REPLACE THE FUEL FILTER

Replacing the fuel filter for preventive maintenance can reduce the risk of dirty fuel causing problems, or a plugged filter causing engine performance or starting problems. Some vehicle manufacturers say you should replace the fuel filter every 50,000 miles. Others say to replace the fuel filter only “as needed,” and some make no filter replacement recommendations at all!

Many professional technicians say you should replace the fuel filter every couple of years to reduce the risk of a plugged fuel line causing driveability or starting problems.

Replacing the fuel filter can also help extend the life of the fuel pump. Why? Because on most fuel injected engines, excess fuel pressure from the fuel rail on the engine is routed back to the fuel tank through a fuel return line. If the fuel is dirty, abrasive particles can recirculate back through the fuel pump again and again accelerating pump wear and causing the fuel pump to fail prematurely. EFI fuel pumps can be VERY expensive to replace and typically cost $200 to $350 plus several hundred dollars labor because the pumps are mounted inside the fuel tank.

Replacement fuel filters typically cost less than $10 for older engines with carburetors, and $15 to $45 for most fuel injected engines, except certain Saturn models that cost $90 and are only available from Saturn dealers. The oddball Saturn fuel filter contains a fuel pressure regulator and is not available from aftermarket suppliers.

A new fuel filter should always be installed if a fuel pump is being replaced, especially if the fuel tank is found to contain rust or sediment.

On older carbureted vehicles, fuel filters are usually held in place by hose clamps on the fuel line. On vehicles with fuel injection, the fuel filter may be attached to the fuel lines with clamps or special “quick lock” couplings (which require a special tool to remove). Quick lock couplings are snap fittings that lock the filter to the fuel line internally. By inserting a special plastic tool into the fitting, the snap lock is released allowing the filter to be pulled out of the fuel line. DO NOT try to force a quick lock fitting apart and DO NOT attempt to pry it apart with a screwdriver because doing so can damage the fuel line and create a possible fuel leak.

older style fuel filter
On older vehicles, simple hose clamps are used to connect the fuel filter.

fuel line disconnect tool
On newer vehicles, the fuel filter line connections use quick couplings.
A special tool like this is required to release the fuel line connections.
The tool fits around the fuel line and is pushed into the coupling to release it.
On some import cars, the fuel lines attach to the fuel filter with banjo fittings. It is very important to replace both copper washers on the banjo fittings when the fuel filter is changed. Reusing the old washers increases the risk of a fuel leak.

WARNING: Gasoline is highly flammable! To minimize the risk of fire when replacing a fuel filter, make sure there are no sparks or open flames nearby (NO SMOKING!). Also, do not allow any fuel to make contact with a hot exhaust pipe, exhaust manifold or the catalytic converter. And if your using a trouble light with an incandescent bulb, keep it well away from the fuel lines when they are opened or trouble light will take on a whole new meaning for you. A 60 watt bulb in a trouble light gets very hot, and could easily ignite fuel that might drip or spray against the bulb. Trouble lights with cool LED lights or a fluorescent bulb would be a much safer choice for this kind of job.

CAUTION: Fuel injection fuel lines are under pressure. On some vehicles the line pressure may be as high as 85 psi or higher. The fuel pressure inside the line needs to be relieved before the fuel line is disconnected, otherwise fuel will spray everywhere.

RELIEVING FUEL PRESSURE

One way to relieve pressure (or at least reduce the pressure in the fuel line), is to let the vehicle sit overnight and open the line in the morning. Be careful, though, because there will still be some residual pressure in the fuel line.

Another way to relieve pressure in the fuel line is to remove the fuel pump fuse, start the engine and let it run until it dies from a lack of fuel pressure. A third method is to attach a fuel pressure gauge to the Schrader valve service fitting on the fuel rail (if the fuel rail has a test fitting) and use the gauge to vent pressure from the fuel system (engine OFF, of course).

Always wear eye protection and wrap a rag around the fuel line connection to deflect any fuel spray.

check fuel filter hose

DON’T FORGET TO INSPECT THE FUEL LINES

When you replace the fuel filter, be sure to inspect the condition of the fuel lines and hoses. Rubber hoses age harden and may develop cracks and leaks after many years of service. If a hose is brittle or is leaking, replace it without delay. The same goes for a steel fuel line that may be cracked and leaking. Fuel leaks are extremely dangerous because they can start fires.

Fuel hose for fuel injected engines has a much higher pressure rating (45 to 100 psi or higher) than fuel hose for older low pressure (4 to 10 psi) carbureted engines. The pressure rating should be printed on the hose. DO NOT use low pressure fuel hose on a fuel injected application. New clamps are also recommended if the hose has external rings clamps.

Know More About Cooling System Repairs

Cooling systems can be your best friend when operating efficiently. Cooling system repairs . . . your worst enemy if you don’t understand how your cooling system works.

Your cooling system performs a critical function. Simply put, it maintains proper engine temperature by circulating coolant through the engine to pick up heat and passing it through a radiator to cool it with air. The coolant passes through a thermostat valve to control flow and possibly over a temperature sensor which controls external air cooling fans.

Cooling systems consist of three main parts:

Cooling System Part #1: Pumping
Your cooling system’s pumping function is handled by its water pump, which keeps the coolant mixture moving.

The main water pump is gear- or belt-driven but, in many cars, a secondary electric water pump is used for improved flow and cooling.

Critical to the pump’s operation is the drive belt that turns it. On most newer cars this is the engine’s timing belt. On older cars, the pump and belt are external and run off the main crankshaft pulley with a “V” or flat belt.

Maintenance of cooling system pumping is limited to scheduled coolant replacement and drive-belt replacement and tension adjustment (external type). Timing-belt-driven pumps should always be replaced at the same time as the timing belt and tensioner.

Cooling System Part #2: Piping
Your cooling system’s piping consists of all hoses, any control valves, the heater core, the radiator and the expansion tank. Because of the materials used and the constant contact with coolant, all parts in this system deteriorate more from time than use.

Maintenance of cooling system piping consists of scheduled coolant replacement, replacement of all hoses on a regular basis and replacement of any plugged or leaking parts.

All hoses should be checked at least twice a year for abrasions, cracks, flexibility and evidence of leakage. Whenever the coolant is drained for replacement or during engine repairs, any suspect hoses should be replaced. All hoses should be replaced at least every few years.

Radiators, expansion tanks, heater cores and control valves are normally only replaced due to leakage or plugging. The condition of these parts should be assessed by a professional since proper functioning is critical to many other systems within your car.

Cooling System Part #3: Temperature Control
Your cooling system’s temperature controls include all coolant temperature sensors, thermostat, radiator or expansion tank cap, cooling fan(s) and fan clutch (if equipped). These cooling system parts function primarily independent of the engine but control the engine either through cooling or by sending control signals to your car’s electronic systems.

The thermostat is a spring-loaded valve that opens and closes based on the temperature of the coolant flowing through it. A high temperature reading followed by a drop to normal temperature (or a continuously low temperature) is a common first sign of a sticking thermostat. However, many other conditions may cause these symptoms, so you need to know how to eliminate each possibility.

The radiator or expansion tank cap is also a spring-loaded valve reacting to system pressure. It serves to maintain proper system coolant level at predetermined pressures. It must always be replaced with an exact replacement cap with the same pressure setting. Never use other caps except for short-term emergencies!

A belt-driven fan blade for pulling air through the radiator is usually on the water pump pulley and should have a fan clutch to control it. The fan clutch allows the fan to turn with the belt at low engine speed and “free-wheel” at higher speeds. A bad fan clutch either doesn’t allow the fan to spin at low speed (overheating in traffic) or doesn’t allow it to free-wheel at high speed (potential overheating on highway or reduced gas mileage).

An electric fan can be either by itself (usually front-wheel drive) or auxiliary (used with a mechanical fan). Both types are controlled via a temperature sensor – in the radiator or upper radiator hose or on the thermostat or water pump housing. This sensor is usually an on/off type switch with a fixed temperature setting. (Some vehicles may have 2-3 settings for multi-speed fans.) This sensor is commonly called an “auxilliary fan switch”.

Other common temperature sensors are: 1) gauge sender (variable output); 2) warning light sender (on/off type); 3) lambda and/or fuel injection sensor(s) (variable to control fuel injection settings); 4) thermo-time switch (cold start valve control). Your car may have other sensors as well.

Temperature control is critical to both performance and emission control. Unfortunately, this system is the most difficult to troubleshoot without proper equipment and diagrams. It’s even more difficult with computers that adjust timing, idle speed, vacuum and fuel delivery automatically to make up for potentially faulty temperature sensor signals.

Maintenance of your cooling system sensors is virtually impossible since there’s nothing really to “maintain”. Keeping them clean both internally (coolant replacement) and externally (engine cleaning) is the best way to ensure trouble-free driving. Checking and replacing all parts at the factory-recommended time or mileage limits helps as well.

A Few Important Things to Remember
Heed these cooling system maintenance tips and you’re well on your way to ensuring your cooling system won’t let you down:

Tip #1: Keep your engine and engine compartment, as well as your radiator fins and grill, as clean as possible. A clean engine runs much cooler – and it’s much easier to work on.

Tip #2: Replace coolant at or before factory recommended intervals with the proper type, mixture and volume of coolant. Always allow the coolant system to rid itself of air before installing the radiator cap.

Tip #3: Replace all cooling system hoses – upper and lower radiator hoses, bypass hoses, heater hoses, manifold coolant hoses and any other hoses on your vehicle – whenever you even suspect there may be a problem. All hoses should be replaced at least every two years.

Tip #4: Replace the thermostat with the original temperature setting equivalent. The electronics in your vehicle may use that setting for other controls. Do not substitute under any circumstances.

Tip #5: Replace the radiator/expansion tank cap with the original pressure setting and OE-type equivalent. Some aftermarket substitutions do not seal and hold pressure properly on foreign-manufactured cars. Again, don’t substitute.

Tip #6: Adjust or replace the water pump drive belt (external) at recommended intervals or more frequently, if required. Check belts whenever you’re working on any coolant system components.

Tip #7: Replace your water pump with an OEM/OES pump at the first signs of trouble or when your timing belt and tensioner are replaced. Watch for signs of overheating – you don’t want to break down in the hot sun when your water pump fails.

Tip #8: Replace the fan clutch and/or fan blade as needed (if applicable). Your car’s temperature gauge is often your best guide as to when your fan clutch needs attention.

Tip #9: Replace temperature sensors as required by diagnosis. Leave troubleshooting of your sensors to experts who have the proper equipment and diagrams.

Tip #10: Keep your entire vehicle properly maintained because of the effect timing, idle speed, exhaust and other systems have on your engine’s temperature. Your car’s cooling system is designed to function with all other systems operating properly. It cannot make up for a poorly operating or overheating engine condition.

Your Cooling System Parts Shopping List
Here’s a list of cooling system repair parts you should consider when repairing your car’s cooling system:

– Coolant –
– Water Pump –
– Water Pump Drive Belt (timing, V-, or flat) –
– Hoses (upper & lower radiator, bypass, heater, manifold coolant, etc.) –
– Radiator –
– Expansion Tank –
– Heater Core –
– Control Valves –
– Temperature Sensors, as applicable* –
– Radiator Cap and/or Expansion Tank Cap –
– Fan Clutch –

*auxilliary fan switch, gauge sender, warning light sender, lambda, fuel injection, thermo-time switch, etc.
Don’t Forget:
Repair articles are added regularly.
Come back often to check for new maintenance topics.

These repair tips are designed only as a starting point.
Please seek the assistance of a professional mechanic
for all repair problems beyond your capabilities.

Should You Know About Troubleshoot & Clean Dirty Fuel Injectors

Clean fuel injectors are a must for peak engine performance, fuel economy and emissions. If the injectors are dirty and can’t deliver their normal dose of fuel, performance, fuel economy and emissions are all going to suffer. Dirty injectors can’t flow as much fuel as clean ones, nor can they delivery the correct spray pattern that is so essential for clean, efficient combustion. The fuel feedback control system will compensate for the leaning effect once it is in closed loop, but it can’t correct the underlying condition that is causing the problem.

The injectors need to be cleaned, if an engine is experiencing any of the classic symptoms of dirty injectors, such as lean misfire, rough idle, hesitation and stumbling on light acceleration, a loss of power, and higher hydrocarbon (HC) and carbon monoxide (CO) emissions.

Lean misfire may also trigger a misfire code and turn on the Check Engine light on 1996 and newer vehicles with OBD II systems. The code often will be a P0300 random misfire code, or you may find one or more misfire codes for individual cylinders, depending on which injectors are most affected.

FUEL INJECTOR CLOGGING

It doesn’t take much of a restriction in an injector to lean out the fuel mixture. A restriction of only 8% to 10% in a single fuel injector can be enough to cause a misfire. When this occurs, unburned oxygen enters the exhaust and makes the O2 sensor read lean. On older multiport systems that fire the injectors simultaneously, the computer compensates by increasing the “on” time of all the injectors, which can create an overly rich fuel condition in the other cylinders.

In turbocharged engines, dirty injectors can have a dangerous leaning effect that may lead to engine-damaging detonation. When the engine is under boost and higher rpms, it needs all the fuel the injectors can deliver. If the injectors are dirty and can’t keep up with the engine’s demands, the fuel mixture will lean out, causing detonation to occur.

All vehicles are vulnerable to injector clogging, but the ones that are most vulnerable and most likely to experience such driveability and emissions problems are older ones with pintle-style multiport injectors. Later injector designs are more resistant to clogging.

In the early pintle-style injectors, the nozzle’s shape and orifice size determine how much fuel flows through the injector and the shape of the spray pattern. Most pintle-style injectors are designed to produce a cone-shaped spray pattern. But, if fuel deposits accumulate in the nozzle area, it can restrict fuel delivery and break up the spray pattern, causing a lean fuel condition and many of the problems just mentioned.

Where do the deposits come from? Mostly from the fuel itself. Gasoline is a mixture of many different hydrocarbons, including oilfins, which are heavy, waxy compounds. The heavier the hydrocarbon, the more energy it yields when it burns. When the engine is shut off, the injectors undergo heat soak. Fuel residue in the injector nozzles evaporates, leaving the waxy oilfins behind. Because the engine is off, there is no cooling air flow through the ports and no fuel flow through the injectors to wash it away, so heat bakes the oilfins into hard varnish deposits. Over time, these deposits can build up and clog the injectors.

The formation of these deposits is a normal consequence of engine operation, so detergents are added to gasoline to help keep the injectors clean. But if a vehicle is used primarily for short-trip driving, the deposits may build up faster than the detergents can wash them away.

On four-cylinder engines, the #2 and #3 injectors are in the hottest location and tend to clog up faster than the end injectors on cylinders #1 and #4. The same applies to the injectors in the middle cylinders in six and eight cylinder engines. The hotter the location, the more vulnerable the injector is to clogging from heat soak. Throttle body injectors are less vulnerable to heat soak because of their location high above the intake manifold plenum.

CHEAP GAS MAKES MATTERS WORSE

To save a few pennies per gallon and to increase the competitive and/or profit margin of gasoline, some suppliers have cut back on the amount of detergent they add to their fuel or have switched to cheaper and less effective additives.

Commonly used deposit-control additives include polysibutylamine, polyisbutylene succinimide and polyisobutylene phenylamine. But these same additives also can build up on intake valve stems causing them to stick. To prevent this from happening, additional additives called “fluidizers” must also be added to the fuel. But, over time, these can contribute to the formation of combustion chamber deposits that raise compression and the engine’s octane requirements.

fuel injector Dirty injectors lean out the fuel mixture and contribute to lean misfire, hesitation and even detonation.
Cleaning should restore like-new performance.

One of the best additives is polyetheramine. It keeps injectors, valves and combustion chambers clean without the help of any additional fluidizers – but it costs more than twice as much as the other commonly used additives.

How much additive does it take to provide an adequate level of protection? Industry sources say the recommended level is about 1,000 parts per million (ppm) of dispersant-detergent in the fuel – which costs the gasoline supplier less than a penny a gallon. Even so, as much as 85% of the gasoline that is being sold contains only one-tenth of the recommended dosage, or only 100 ppm of additive. Consequently, using cheap gas contributes to the formation of injector deposits.

clean fuel injectors Cleaning injectors off-car takes more time and effort, but usually delivers much better results than on-car cleaning.

BENEFITS OF CLEANING FUEL INJECTORS

The benefits realized by injector cleaning obviously will vary depending on the condition of the injectors prior to cleaning and how badly they were clogged. Injectors that are really dirty should show more of a noticeable improvement in performance than ones that have only a light accumulation of deposits. Either way, performance, fuel economy and emissions should all be better after a cleaning.

Most high-mileage engines as well as engines that are used mostly for short trip stop-and-go driving are the most likely prospects for injector cleaning. Some experts recommend cleaning the injectors every 25,000 to 30,000 miles to keep them flowing at peak efficiency.

OTHER COMPONENTS THAT MAY NEED CLEANING

Another component that also may need to be cleaned to remove fuel varnish is the throttle body. Fuel vapor rising up through the intake manifold can accumulate and vaporize around the throttle plate and air bypass circuits, causing a change in the idle air/fuel mixture. Sometimes you can see the deposits, and sometimes you can’t. Either way, cleaning the throttle body and intake tract also may be necessary to fully restore engine performance, idle quality and emissions. An aerosol cleaning solvent works well here.

The intake valves and combustion chambers should also be cleaned when you do the injectors to remove deposits that may also be contributing to driveability and emissions problems. Deposits on the backs of intake valves can act like a sponge and absorb fuel, causing a momentary hesitation when the throttle is suddenly opened. Combustion chamber deposits increase compression and the risk of engine-damaging detonation (spark knock).

Engines that burn oil typically will have heavy intake valve and combustion chamber deposits that do not respond well to normal levels of detergent in gasoline. Additional cleaner is needed, which can be added to the fuel tank or run directly through the injectors.

To remove carbon deposits from the intake valves and combustion chambers, use a “top cleaner” type of product and follow the instructions, or use equipment that is designed to clean the upper engine (such as a Motorvac Decarbon machine).

clean fuel injectors Direct injection fuel injectors have very precise spray patterns and are even more sensitive to deposits than regular injectors.

injector spray patterns Injector spray patterns can show if any are misshapen or contain streamers of unvaporized liquid.

Some experts recommend replacing the spark plugs after doing an on-car injection cleaning or decarbon treatment. The residue that is loosened and washed away by the solvent may increase the risk of plug fouling. Changing the oil and filter is also a good idea following a cylinder decarbon treatment because some of the solvent will get past the rings and end up in the crankcase.

FUEL INJECTOR CLEANING OPTIONS

Should you clean the injectors in place or remove them and use some type of injector cleaning machine? It depends.

The easiest route is to clean the injectors in place because you do not have to remove the injectors (which can be a real chore on some import engines). Running cleaner through the injectors while the engine is running also removes many of the deposits on the valves and inside the combustion chambers. This eliminates the need for an extra cleaning step if the engine is full of carbon deposits. The job takes only 10 to 15 minutes, and you can usually tell right away if the treatment addressed the problem (engine runs smoother, idle misfire gone, etc.).

When doing the cleaning procedure itself, you must use pressurized equipment to feed the solvent directly into the fuel rail while the engine is running. This means you either have to disable the fuel pump and plug the fuel return line, or install a U-tube so the fuel will recirculate right back to the tank. Disabling the fuel pump can set a fault code on some cars, requiring you to clear the code after the job is done.

Easy as it is, there are some limitations with on-car injector cleaning. One is that badly clogged injectors may not pass enough solvent during a normal cleaning cycle to be thoroughly cleaned. Some baked-on deposits can be very difficult to remove, requiring you to prolong or repeat the cleaning process. And if on-car cleaning does not work? You will have to remove the injectors and have them cleaned on an injector cleaning machine – or replace them.

Another limitation with on-car injector cleaning is that you may have to do some additional tests to confirm that the injectors responded well enough to your cleaning efforts. A test drive may be needed to see if the driveability symptoms have been eliminated, or you may have to check emissions to make sure HC and CO levels are back to normal. A power balance test is another way to confirm engine performance and check for weak cylinders (there should be less than a 10% power variation between cylinders). An injector pressure drop test will tell you if the injectors are flowing evenly or not.

There may be some risk to the vehicle’s fuel system when using concentrated solvent to clean the injectors in place. Most equipment suppliers say to disconnect and plug the fuel return line so that solvent does not circulate back to the fuel tank. Strong solvents may attack rubber and plastic components in the fuel pump, regulator and fuel lines, creating additional problems that you don’t need.

On-car injector cleaning also involves some risk to the person who’s performing the service. You have to disconnect pressurized fuel lines, make sure there are no fuel leaks, and feed high-pressure solvent (which is just as flammable as gasoline) into the engine while the engine is running. Safety precautions should always include eye protection, making sure there are no open sources of ignition (sparks) nearby, and avoiding direct exposure with the cleaning solvent.

OFF-CAR FUEL INJECTOR CLEANING

Injectors that are really dirty may not respond well to on-car cleaning. You may have to use a more powerful solvent and/or longer cycle time to loosen the baked-on deposits. That is where an off-car injector cleaning machine really helps.

Off-car injector cleaning is a more expensive service because of the labor involved to remove the injectors (which can be considerable on some applications), and it requires special equipment that can cost anywhere from $4,000 to $8,300.

fuel injector flow testing

Many shops charge between $25 and $35 per injector for off-car cleaning – which makes it more costly than on-car cleaning. But it also can motorists a lot of money because off-car cleaning is a lot cheaper than replacing the injectors with new ones (which can cost hundreds of dollars a set!).

Off-car injector cleaning can often restore dirty injectors that fail to respond to on-car cleaning. That is why some shops do only off-car cleaning. They do not want to have to clean the injectors twice. Off-car cleaning takes more time (typically 30 to 45 minutes after the injectors have been removed), and most machines have an ultrasonic bath that can be used to soak badly clogged injectors. Some machines also reverse-flush the injectors, which provides an added measure of cleaning.

Another reason for using off-car cleaning equipment is that the injectors can be flow-tested after they have been cleaned to verify their performance. The injectors typically are mounted on a test manifold and energized to spray solvent into clear graduated cylinders. By comparing the volume of fuel delivered, it is easy to see if all the injectors are flowing evenly.

As a rule, you should see less than 5% to 7% variation between injectors (some performance engine builders aim for 1% or less variation between injectors!). If an injector is not passing as much liquid as its companions, you can subject it to more cleaning. And, if it fails to respond to additional cleaning, there is no guesswork about which injector needs to be replaced.

Flow-testing also allows you to compare the actual flow rate of each injector to factory specifications. If the flow is within specifications, you know the injector should perform properly when it is reinstalled back in the engine. Flow-testing also is a good way to make sure the injectors are the right ones for the engine (one or more injectors may have been previously replaced by someone else).

A flow test on the cleaning equipment allows you to see each injector’s spray pattern. If you see a normal, cone-shaped mist, you know the injector is flowing properly. If you see streamers of unvaporized liquid in the spray pattern, you know additional cleaning is needed or the injector needs to be replaced.

Know More About Troubleshoot Fuel Injectors

Clean fuel injectors are a must for peak engine performance, fuel economy and emissions. If the injectors are dirty and cannot deliver their normal dose of fuel, then performance, fuel economy and emissions are all going to suffer. Dirty injectors cannot flow as much fuel as clean ones, nor can they deliver the correct spray pattern that is so essential for clean, efficient combustion. The fuel feedback control system will compensate for the leaning effect once it is in closed loop, but it cannot correct the underlying condition that is causing the problem.

The injectors need to be cleaned if an engine is experiencing any of the classic symptoms of dirty injectors, such as lean misfire, rough idle, hesitation and stumbling on light acceleration, a loss of power, and higher hydrocarbon (HC) and carbon monoxide (CO) emissions.

Lean misfire may also trigger a misfire code and turn on the Check Engine light on 1996 and newer vehicles with OBD II systems. The code often will be a P0300 random misfire code, or you may find one or more misfire codes for individual cylinders, depending on which injectors are most affected.
Fuel Injector Clogging

It does not take much of a restriction in an injector to lean out the fuel mixture. A restriction of only 8% to 10% in a single fuel injector can be enough to cause a misfire. When this occurs, unburned oxygen enters the exhaust and makes the O2 sensor read lean. On older multiport systems that fire the injectors simultaneously, the computer compensates by increasing the on-time of all the injectors, which can create an overly rich fuel condition in the other cylinders.
In turbocharged engines, dirty injectors can have a dangerous leaning effect that may lead to engine-damaging detonation. When the engine is under boost and higher rpm, it needs all the fuel the injectors can deliver. If the injectors are dirty and cannot keep up with the engine’s demands, the fuel mixture will lean out, causing detonation to occur.
All vehicles are vulnerable to injector clogging, but the ones that are most vulnerable and most likely to experience such driveability and emissions problems are older ones with pintle-style multiport injectors. Later injector designs are more resistant to clogging. In the early pintle-style injectors, the nozzle shape and orifice size determine how much fuel flows through the injector and the shape of the spray pattern. Most pintle-style injectors are designed to produce a cone-shaped spray pattern. But, if fuel deposits accumulate in the nozzle area, it can restrict fuel delivery and break up the spray pattern, causing a lean fuel condition and many of the problems just mentioned.
Fuel Injector Deposits

Where do the deposits come from? Mostly from the fuel itself. Gasoline is a mixture of many different hydrocarbons, including oilfins, which are heavy, waxy compounds. The heavier the hydrocarbon, the more energy it yields when it burns. When the engine is shut off, the injectors undergo heat soak. Fuel residue in the injector nozzles evaporates, leaving the waxy oilfins behind. Because the engine is off, there is no cooling airflow through the ports and no fuel flow through the injectors to wash it away, so heat bakes the oilfins into hard varnish deposits. Over time, these deposits can build up and clog the injectors.
dirty fuel injectors
The formation of these deposits is a normal consequence of engine operation, so detergents are added to gasoline to help keep the injectors clean. But if a vehicle is used primarily for short-trip driving, the deposits may build up faster than the detergents can wash them away.
On four-cylinder engines, the #2 and #3 injectors are in the hottest location and tend to clog up faster than the end injectors on cylinders #1 and #4. The same applies to the injectors in the middle cylinders in six- and eight-cylinder engines. The hotter the location, the more vulnerable the injector is to clogging from heat soak. Throttle body injectors are less vulnerable to heat soak because of their location high above the intake manifold plenum.
Detergents In Gasoline

To save a few pennies per gallon and to increase the competitive and/or profit margin of gasoline, some suppliers have cut back on the amount of detergent they add to their fuel or have switched to cheaper and less-effective additives.
Commonly used deposit-control additives include polysibutylamine, polyisbutylene succinimide and polyisobutylene phenylamine. But these same additives also can build up on intake valve stems causing them to stick. To prevent this from happening, additional additives called fluidizers also must be added to the fuel. But, over time, these can contribute to the formation of combustion chamber deposits that raise compression and the engine’s octane requirements.
Dirty injectors lean out the fuel mixture and contribute to lean misfire, hesitation and even detonation. Cleaning should restore like-new performance.
One of the best additives is polyetheramine. It keeps injectors, valves and combustion chambers clean without the help of any additional fluidizers – but it costs more than twice as much as the other commonly used additives.
How much additive does it take to provide an adequate level of protection? Industry sources say the recommended level is about 1,000 parts per million (ppm) of dispersant-detergent in the fuel – which costs the gasoline supplier less than a penny a gallon. Even so, as much as 85% of the gasoline that is being sold contains only one-tenth of the recommended dosage, or only 100 ppm of additive. Consequently, using cheap gas contributes to the formation of injector deposits.
Fuel Injector Cleaning
The benefits realized by injector cleaning obviously will vary depending on the condition of the injectors prior to cleaning and how badly they were clogged. Injectors that are really dirty should show more of a noticeable improvement in performance than ones that have only a light accumulation of deposits. Either way, performance, fuel economy and emissions should all be better after a cleaning.
Most high-mileage engines, as well as engines that are used mostly for short-trip, stop-and-go driving, are the most likely prospects for injector cleaning. Some experts recommend cleaning the injectors every 25,000 to 30,000 miles to keep them flowing at peak efficiency.
More Fuel Injection Cleaning Options

Another component that also may need to be cleaned to remove fuel varnish is the throttle body. Fuel vapor rising up through the intake manifold can accumulate and vaporize around the throttle plate and air bypass circuits, causing a change in the idle air/fuel mixture. Sometimes you can see the deposits, and sometimes you cannot. Either way, cleaning the throttle body and intake tract also may be necessary to fully restore engine performance, idle quality and emissions. An aerosol cleaning solvent works well here.
The intake valves and combustion chambers also should be cleaned when you do the injectors to remove deposits that may also be contributing to driveability and emissions problems. Deposits on the backs of intake valves can act like a sponge and absorb fuel, causing a momentary hesitation when the throttle is suddenly opened. Combustion chamber deposits increase compression and the risk of engine-damaging detonation (spark knock).
Engines that burn oil typically will have heavy intake valve and combustion chamber deposits that do not respond well to normal levels of detergent in gasoline. Additional cleaner is needed, which can be added to the fuel tank or run directly through the injectors.
To remove carbon deposits from the intake valves and combustion chambers, use a top cleaner type of product and follow the instructions, or use equipment that is designed to clean the upper engine.
Direct injection fuel injectors have very precise spray patterns and are even more sensitive to deposits than regular injectors.
Note: Some experts recommend replacing the spark plugs after doing an on-car injection cleaning or decarbon treatment. The residue that is loosened and washed away by the solvent may increase the risk of plug fouling. Changing the oil and filter is also a good idea following a cylinder decarbon treatment because some of the solvent will get past the rings and end up in the crankcase.
Fuel Injector Cleaning Options

Should you clean the injectors in place or remove them and use some type of injector cleaning machine? It depends.
The easiest route is to clean the injectors in place because you do not have to remove them (which can be a real chore on some import engines). Running cleaner through the injectors while the engine is running also removes many of the deposits on the valves and inside the combustion chambers. This eliminates the need for an extra cleaning step if the engine is full of carbon deposits. The job takes only 10 to 15 minutes, and you can usually tell right away if the treatment addressed the problem (engine runs smoother, idle misfire gone, etc.).
When doing the cleaning procedure itself, you must use pressurized equipment to feed the solvent directly into the fuel rail while the engine is running. This means you either have to disable the fuel pump and plug the fuel return line, or install a U-tube so the fuel will recirculate right back to the tank. Disabling the fuel pump can set a fault code on some cars, requiring you to clear the code after the job is done.
Easy as it is, there are some limitations with on-car injector cleaning. One is that badly clogged injectors may not pass enough solvent during a normal cleaning cycle to be thoroughly cleaned. Some baked-on deposits can be very difficult to remove, requiring you to prolong or repeat the cleaning process. And if on-car cleaning does not work? You will have to remove the injectors and try to clean them on an injector cleaning machine – or replace them.
Another limitation with on-car injector cleaning is that you may have to do some additional tests to confirm that the injectors responded well enough to your cleaning efforts. A test drive may be needed to see if the driveability symptoms have been eliminated, or you may have to check emissions to make sure HC and CO levels are back to normal. A power balance test is another way to confirm engine performance and check for weak cylinders (there should be less than a 10% power variation between cylinders). An injector pressure drop test will tell you if the injectors are flowing evenly or not.
There may be some risk to the vehicle’s fuel system when using concentrated solvent to clean the injectors in place. Most equipment suppliers say to disconnect and plug the fuel return line so that solvent does not circulate back to the fuel tank. Strong solvents may attack rubber and plastic components in the fuel pump, regulator and fuel lines, creating additional problems that you don’t want.
Be Cautious During Cleaning
On-car injector cleaning also involves some risk to the person who is performing the service. You have to disconnect pressurized fuel lines, make sure there are no fuel leaks, and feed high-pressure solvent (which is just as flammable as gasoline) into the engine while the engine is running. Safety precautions should always include eye protection, making sure there are no open sources of ignition (sparks) nearby, and avoiding direct exposure with the cleaning solvent.
dirty fuel injector
Clean Fuel Injectors Off Car

Injectors that are really dirty may not respond well to on-car cleaning. You may have to use a more powerful solvent and/or longer cycle time to loosen the baked-on deposits. That is where an off-car injector cleaning machine really pays for itself.
Off-car injector cleaning is a more expensive service because of the labor involved to remove the injectors (which can be considerable on some applications), and the special fuel injector cleaning equipment that is required.
Off-car injector cleaning can often restore dirty injectors that fail to respond to on-car cleaning. That is why some shops do only off-car cleaning. They don’t want to have to clean the injectors twice. Off-car cleaning takes more time (typically 30 to 45 minutes after the injectors have been removed), and most machines have an ultrasonic bath that can be used to soak badly clogged injectors. Some machines also reverse-flush the injectors, which provides an added measure of cleaning.
Another reason for using off-car cleaning equipment is that the injectors can be flow-tested after they have been cleaned to verify their performance. The injectors typically are mounted on a test manifold and energized to spray solvent into clear graduated cylinders. By comparing the volume of fuel delivered, it is easy to see if all the injectors are flowing evenly.
Observing the spray patterns of a set of injectors can show you at a glance if any are misshapen or contain streamers of unvaporized liquid.
As a rule, you should see less than 5% to 7% variation between injectors (some performance engine builders aim for 1% or less variation between injectors!). If an injector is not passing as much liquid as its companions, you can subject it to more cleaning. And, if it fails to respond to additional cleaning, there is no guesswork about which injector needs to be replaced.
fuel injection flow testing

Fuel Injector Flow Testing

Flow-testing also allows you to compare the actual flow rate of each injector to factory specifications. If the flow is within specifications, you know the injector should perform properly when it is reinstalled back in the engine. Flow-testing also is a good way to make sure the injectors are the right ones for the engine (one or more injectors may have been previously replaced by someone else).
A flow test on the cleaning equipment allows you to see each injector spray pattern. If you see a normal, cone-shaped mist, you know the injector is flowing properly. If you see streamers of unvaporized liquid in the spray pattern, you know additional cleaning is needed or the injector needs to be replaced.
Injector cleaning will be an ongoing need as long as engines are equipped with fuel injectors. Even the new generation of direct injection gasoline engines that are now being built are vulnerable to fuel deposits. So be on the alert for the symptoms of dirty injectors and do not hesitate to have the injectors cleaned for preventive maintenance.

Learn More About Diagnose Fuel Gauge

Nothing is more aggravating than a fuel gauge that doesn’t give an accurate reading, especially when the gauge shows there’s still fuel in the tank when there really is not. Faulty readings can be caused by a bad sending unit, a problem with the gauge, or shorts, opens or weak connections in the wiring that links the two together. But which one is it?

In 1904, the first float arm gas gauge appeared. A float mounted on a hinged arm moved a mechanical pointer on gauge on the outside of the fuel tank to indicate the fuel level. The idea was taken one step further when vehicles started to get better electrical systems by connecting the hinged float arm to a rheostat. This allows an electrically operated fuel gauge to be mounted in the vehicle’s dashboard. And that’s the basic operating principle that is still in use today.
There are essentially three types of fuel gauges: analog resistance (used almost universally up through the early 1980s), analog magnetic (introduced in the ’80s) and digital/graphic electronic gauges (also introduced in the ’80s and used to this day).

ANALOG FUEL GAUGES

Analog fuel gauges use a heated bimetal strip to move the indicator needle on the fuel gauge. The amount of current flowing through the gauge heats up the bimetal strip. The strip expands and determines how far the needle moves. Voltage is supplied to the gauge by a small voltage regulator in the instrument panel which reduces circuit voltage to about five volts. The voltage regulator also supplies the temperature and oil pressure gauges.

The amount of current that flows through the fuel gauge is controlled by the ground circuit provided by the sending unit in the fuel tank. As the fuel level inside the tank goes up and down, the hinged arm that’s attached to the float rotates a rheostat. This changes the amount of resistance in the ground circuit which allows more or less current to flow through the gauge.

In Ford and Chrysler applications, the sending unit increases resistance as the fuel level drops and decreases resistance as the fuel level goes up. When the fuel tank is empty, for example, resistance is high (around 73 ohms). High resistance reduces the current that flows through the fuel gauge, producing little or no movement in the needle. When the fuel tank is full, the sending unit has low resistance (around 8 ohms) so more current flows through the fuel gauge. This heats up the bimetal strip causing maximum needle deflection. Now the needle moves all the way to the full mark.

A shorted sending unit or a short in the wiring between the sending unit and gauge would reduce circuit resistance causing the fuel gauge to read full. And with nothing to slow the amps, the circuit would probably overload and blow a fuse. An open in the sending unit or wiring, on the other hand, would prevent the needle from moving at all and the gauge would read empty.

With General Motors analog resistance fuel gauges, the basic operating principle is the same but electrically opposite. Resistance in the sending unit decreases as the fuel level drops, and increases and the level goes up. When the tank is empty, the sending unit reads about zero ohms, and when the tank is full it reads about 90 ohms. Gauge operation is also the same with maximum needle deflection corresponding to minimum resistance in the sending unit. In this case, maximum deflection is required to move the needle all the way over to the empty mark.

A short in the sending unit or wiring on a GM system would cause the fuel gauge to read empty, therefore, while an open in the sending unit circuit would make the gauge read full.

MAGNETIC FUEL GAUGES

The successor to the resistance type fuel gauge is the magnetic fuel gauge. Instead of having a heated bimetal strip to deflect the indicator needle, the base of the needle has a small magnet that “floats” in a magnetic field created by three coils. The coils are fed voltage through a terminal that’s usually marked “B+” on the back of the gauge. Inside, the voltage follows a split path. Part of it passes through all three coils to ground and part of it goes through only the first coil then on through the sending unit to ground. Depending on the resistance in the sending unit circuit, the strength of the magnetic field created by the first coil compared to the other two shifts the magnetic field one way or the other to deflect the needle on the fuel gauge.

The primary advantages of magnetic gauges (fuel as well as temperature and oil pressure) compared to the resistance variety are faster response and more accurate readings. The resistance variety can take up to two minutes to respond to a change.

The sending unit that’s used with a magnetic fuel gauge is essentially the same as before but with higher resistance values. And most follow the GM format of high resistance when the tank is full. On a 1980s vintage Chrysler application, for example, the sending unit reads 145 ohms when the tank is full and 22.5 ohms when the tank is empty.

digital fuel gauge
Digital gauges may not be as accurate as analog gauges.
The fuel level shown is a calculation based on the sending unit input.
ELECTRONIC FUEL GAUGES

Electronic fuel gauges use vacuum fluorescent or LCD graphic displays to indicate the fuel level. Many also read E, 1/2 and F. Electronic displays usually have their own self-contained voltage regulator in the fuel gauge control module. The basic operating principle for electronic fuel gauges is essentially same as that of the other two types in that the tank mounted sending unit produces a variable resistance ground path. The module monitors the current through the sending unit and decides which display circuits to energize to show the fuel level.

Most electronic fuel gauges have limited self-diagnostics. When the key is turned on, most units light up all their display pixels as a way of checking the display itself (like a bulb check). Others go a step further. On Ford, for instance, the fuel gauge will flash if the module detects an open or short in the sending unit circuit.

LOW FUEL WARNING LIGHT

Low fuel warning lights are worth mentioning because they’re wired into the fuel gauge. On Fords, for example, a low fuel warning switch assembly illuminates a warning light when the fuel gauge reads below 1/4 full. On late model electronic fuel gauges, the light typically comes on when there is about 1-1/2 to two gallons of fuel left in the tank.

FUEL GAUGE DIAGNOSIS

If the fuel gauge does not change (always reads the same, always reads empty or full), or behaves erratically, the list of possible causes include a defective voltage supply to the gauge (instrument voltage regulator), a bad gauge, a defective sending unit, a wiring problem between the gauge and sending unit, or a poor ground connection.

If the temperature and oil pressure gauges are also affected, the problem is not in the fuel gauge or sending unit. It is in the instrument voltage regulator or instrument panel wiring. To get at the voltage regulator, you have to remove the instrument panel.

Check the voltage output of the regulator with a volt meter. If it isn’t within specs (usually around 5 volts), it may have a weak ground connection or an open in the resistor wire that supplies it voltage. Refer to a shop manual for the resistance wire specs. and where to find and check the regulator.

If only the fuel gauge is acting up, you can rule out the voltage regulator as a possible cause. The problem is either in the gauge itself, the sending unit or the wiring in between.

It makes no difference whether you start with the fuel gauge or the sending unit to begin your diagnosis. The best advice is to start with which ever one is the most easily accessible. If you have to drop the fuel tank to get at the sending unit, you can save yourself some effort by starting with the fuel gauge. But if the sending unit connector can be reached without having to drop the tank, then start there.
The fuel level sending unit inside the fuel tank
can sometimes stick giving a false indication to the fuel gauge.
It may read high or it may read low.
If it reads high, you might run out of gas!
FUEL GAUGE SENDING UNIT CHECKS

There are several ways to find out whether or not the sending unit is doing its job. One is to unplug the sending unit connector and hook your ohmmeter up to the sending unit terminals. Note the resistance reading. If it isn’t within the range of minimum and maximum specs, you’ve found the problem. Replace the sending unit.

To tell how much fuel is in the tank, you can remove the gas cap and slide a piece of wire or dowel rod down the filler neck like a dipstick. Needless to say, you’d better not have a cigarette dangling from your lips when you do this or your widow will be reading your obituary in the newspaper. You don’t need an exact indication, just an approximation. Or you can drain the tank or fill it up, checking the resistance readings before and afterwards to see if the sending unit makes the appropriate response.

Another alternative is to remove the sending unit from the tank and bench test it using an ohmmeter. Moving the float back and forth between the full and empty positions should produce a corresponding change in resistance. On Ford, for example, the sending unit should read between 8 and 12 ohms when the float is at the full position, and 60 to 86 ohms when it’s at the empty position. No change, “skips” in the reading or readings that are out of range would all tell you a new sending unit is needed.

NOTE: “Bad gas” can occasionally cause fuel sending unit failures. The amount of sulfur in the fuel may corrode the contacts on the sending unit, causing dead spots or a loss of signal. Bad gas can also cause fuel pump failures.

Nonelectrical problems that can affect the sending unit include a leak in the float (it will sink or read low), a binding or broken float arm, or damage to the fuel tank that prevents the float from moving or reading the level accurately.

What if the sending unit checks out okay? Then the problem is in the wiring or the gauge. Corroded or loose wiring terminals, opens or shorts in the wiring can be isolated by checking wiring continuity. That leaves the gauge.

FUEL GAUGE CHECKS

Like the sending unit, the gauge can be checked several ways.

One way is to remove the sending unit from the tank, reconnect it, turn the key on and move the float arm up and down while watching for a change in the gauge reading. If the gauge hasn’t responded within a couple of minutes, you’ve confirmed the fact that you have a problem. But you’re still at square one because you don’t know where it is.

To check the gauge, you can simulate input from the sending unit. A test box that simulates various resistance readings can be used in place of the sending unit to test gauge response. Such testers are designed primarily for the older resistance type gauges. They include: GM J-24538A, Chrysler C-3826A and Ford 21-0015.

If you don’t have access to a tester for checking your fuel gauge, you can fabricate some resistor jumper wires by buying a 5 ohm and 80 ohm resistor at a local radio parts store. Connect each resistor to a fused jumper wire and use them to simulate high and low sending unit readings. The jumper wires (or test box) can be used either at the gauge or sending unit.

If the gauge doesn’t respond appropriately when the resistance in the sending unit circuit is changed, check the hot terminal at the gauge to see if it’s receiving voltage. If it is but the needle doesn’t move, then it’s time for a new gauge.

With resistance and magnetic gauges, you can also check the gauge’s internal resistance with an ohmmeter. You should generally find somewhere between 10 to 15 ohms resistance. No resistance would indicate a short in the gauge while very high resistance would indicate an open

The work System Of Electronic Fuel Injection

Electronic fuel injection (EFI) replaced carburetors back in the mid-1980s as the preferred method for supplying air and fuel to engines. The basic difference is that a carburetor uses intake vacuum and a pressure drop in the venturi (the narrow part of the carburetor throat) to siphon fuel from the carburetor fuel bowl into the engine whereas fuel injection uses pressure to spray fuel directly into the engine.

With a carburetor air and fuel are mixed together as air is pulled through the carburetor by the engine. The air/fuel mixture then travels through the intake manifold to the cylinders. One of the drawbacks of this approach is that the intake manifold is wet (contains droplets of liquid fuel) so fuel can puddle in the plenum area of the manifold when a cold engine is first started. The twists and turns of the intake runners can also cause the air and fuel mixture to separate as if flows to the cylinders, resulting in uneven fuel mixtures between cylinders. The center cylinders typically run slightly richer than the end cylinders, which makes tuning for peak fuel economy, performance and emissions more difficult with a carburetor.
THROTTLE BODY INJECTION

With Throttle Body Injection (TBI), one or two injectors mounted in the throttle body spray fuel into the intake manifold. Fuel pressure is created by an electric fuel pump (usually mounted in or near the fuel tank), and the pressure is controlled by a regulator mounted on the throttle body. Fuel is sprayed into the engine when the engine computer energizes the injector(s), which occurs in a rapid series of short bursts rather than a continuous stream. This produces a buzzing noise from the injectors when the engine is running.

Because of this setup, the same fuel distribution issues that affect carburetors also affect TBI systems. However, TBI systems have better cold start characteristics than a carburetor because they provide better atomization and do not have a troublesome choke mechanism. A TBI system also makes it easier for an electronic engine control system to regulate the fuel mixture than an electronic feedback carburetor. Throttle Body Injection systems were only used briefly during the 1980s as US vehicle manufacturers transitioned from carburetors to fuel injection to meet emission regulations. By the late 1980s, most TBI systems were replaced with Multiport Injection (MPI) fuel injection systems.

MULTIPORT FUEL INJECTION

With MultiPort Injection systems, there is a separate fuel injector for each cylinder. The advantage of this approach is that fuel is sprayed directly into the cylinder head intake port. Since only air flows through the intake manifold, the intake manifold remains dry and there are no problems with fuel puddling when the engine is cold or fuel separation causing uneven fuel mixtures in the center and end cylinders. This allows the fuel mixture to be much more even in all of the cylinders for better fuel economy, emissions and performance.

Some early production multiport fuel injection systems were purely mechanical and date back to the 1950s (1957 Corvette with Rochester Fuel Injection , for example, and Bosch D-Jetronic and K-Jetronic systems with their mechanical fuel distributors and injectors). Later fuel injection systems such as the Bosch L-Jetronic systems of the late 1970s replaced mechanical injectors with electronic injectors. Today, all production EFI systems are fully electronic with computer controls and electronic injectors.

Most of the EFI systems that were offered in the late 1980s and early 1990s fire all of the injectors simultaneously, typically once every revolution of the crankshaft. The more sophisticated Sequential Fuel Injection (SFI) systems that came later fire each injector separately, usually just as the intake valve is opening. This allows much more precise fuel control for better fuel economy, performance and emissions.

GASOLINE DIRECT FUEL INJECTION

In the 2000s, some vehicle manufacturers began offering a new type of fuel injection system called Gasoline Direct Injection (GDI). With this setup, a separate injector is still used for each cylinder but the injectors are relocated on the engine to spray fuel directly into the combustion chamber rather than the intake port. This is similar to a diesel engine that sprays fuel directly into the cylinder. The advantage with this approach is a significant improvement (as much as 15 to 25 percent!) in fuel economy and power. However, it requires special high pressure fuel injectors and much higher operating pressures. Some current examples of direct fuel injection include VW TDI engines, Mazda direct injection engines, General Motors EcoTech engines and Ford EcoBoost engines.

FUEL INJECTOR PULSES

The relative richness or leanness of the fuel mixture in a fuel injected engine is determined by varying the duration of the injector pulses (called pulse width). The longer the pulse width, the greater the volume of fuel delivered and the richer the mixture.

Injector timing and duration is controlled by the engine computer. The computer uses input from its various engine sensors to regulate fuel metering and to change the air/fuel ratio in response to changing operating conditions. The primary sensor for fuel mixture control is the Oxygen sensor. The O2 sensor generates a RICH or LEAN signal that the engine computer uses to adjust the fuel mixture. For more information about feedback fuel control and fuel trim adjustments, see What Is Fuel Trim?

The computer is calibrated with a fuel delivery program that is best described as a three-dimensional map. The program directs the computer as to how long to make the injector pulses as engine speed and load change. During start-up, warm-up, acceleration and increased engine load, the map typically calls for a richer fuel mixture. When the engine is cruising under light load, the map allows for a leaner fuel mixture to improve fuel economy. And when the vehicle is decelerating and there is no load on the engine, the map may allow the computer to momentarily turn the injectors off altogether.

The programming that controls the EFI system is contained on a PROM (Program Read Only Memory) chip inside the engine computer. Replacing the PROM chip can change the calibration of the EFI system. This is sometimes necessary to update factory programming or to correct a drivability or emissions problem. The PROM chip on some vehicles can also be replaced with aftermarket performance chips to improve engine performance, too.

On many 1996 and newer vehicles, the programming is on an EEPROM (Electronically Ereasable Program Read Only Memory) chip in the computer. This allows the programming to be updated or changed by reflashing the computer. The new programming is downloaded into the computer through the OBD II Diagnostic Connector using a scan tool or J2534 reprogramming tool.

FUEL INJECTIN SENSOR INPUTS

Electronic fuel injection requires inputs from various engine sensors so the computer can determine engine speed, load and operating conditions. This allows the computer to adjust the fuel mixture as needed for optimum engine operation.

There are two basic types of EFI systems: Speed-Density systems and Mass Airflow systems. Speed density systems such as those found on many Chrysler engines and some GM engines do not actually measure airflow into the engine, but estimate airflow based on inputs from the Throttle Position Sensor (TPS), Manifold Absolute Pressure (MAP) sensor and engine RPM. The advantage with this approach is that the engine does not require an expensive airflow sensor, and the air/fuel mixture is less affected by small air leaks in the intake manifold, vacuum plumbing or throttle body.

Ford mass airflow sensor
A Ford mass airflow sensor also includes an Inlet Air Temperature (IAT) sensor inside.

With mass airflow systems, some type of airflow sensor is used to directly measure airflow into the engine. It may be a mechanical flap style airflow sensor, a hot wire airflow sensor or a vortex airflow sensor. The computer also uses inputs from all of its other sensors, but relies primarily on the airflow sensor to control the fuel injectors.

An EFI system will usually run without a signal from the MAP sensor, but it will run poorly because the computer has to rely on its other sensor inputs to estimate airflow. A common problem with MAF sensors is a buildup of dirt or varnish on the heated wire inside the sensor. Cleaning the MAF wire inside the sensor with electronics cleaner will often restore normal operation and cure a lean condition caused by a dirty airflow sensor.

On both types of systems (speed-density and mass airflow), input from the Heated Oxygen sensor (HO2) is also key for maintaining the optimum air/fuel ratio. The oxygen sensor (or Air/Fuel sensor on many newer vehicles) is mounted in the exhaust manifold and monitors unburned oxygen levels in the exhaust as an indicator of the relative richness or leanness of the fuel mixture. On V6 and V8 engines, there will be a separate oxygen sensor for each bank of cylinders, and on some straight six cylinder engines (BMW for example), there may be separate oxygen sensors for the first three cylinders and the last three cylinders. The feedback signal from the oxygen sensor or air/fuel sensor is used by the engine computer to constantly fine tune the fuel mixture to optimum fuel economy and emissions.

When the oxygen sensor tells the computer the engine is running lean (higher levels of unburned oxygen in the exhaust), the computer compensates by richening up the fuel mixture (increasing the pulse width of the injectors). If the engine is running rich (less oxygen in the exhaust), the computer shortens the pulse width of the injectors to lean the fuel mixture.

Input about the position of the throttle is provided by the Throttle Position Sensor (TPS). It is located on the side of the throttle body and uses a variable resistor that changes resistance as the throttle opens and closes.

Engine load is measured by the Manifold Absolute Pressure (MAP) sensor. It may be mounted on the intake manifold or attached to the intake manifold with a vacuum hose.

The temperature of the air entering the engine must also be monitored to compensate for changes in air density that occur (colder air is denser than hot air). This is monitored by an Inlet Ait Temperature (IAT) or Manifold Air Temperature (MAT) sensor, which may be built into the airflow sensor or mounted separately on the intake manifold.

Coolant temperature is monitored by the Coolant Temperature Sensor (CTS). This tells the computer when the engine is cold and when it is at normal operating temperature. The computer needs to know the temperature because a cold engine requires a richer fuel mixture when it is first started. When the coolant reaches a certain temperature, the engine goes into Closed Loop operation, which means it starts using inputs from the oxygen sensors to fine tune the fuel mixture. When it is operating in Open Loop (when cold or when there is no signal from the coolant sensor), the fuel mixture is fixed and does not change.

Faulty inputs from any of the engine’s sensors may cause drivability, emissions or performance problems. Many sensor problems will set a Diagnostic Trouble Code (DTC) and turn on the Check Engine Light. Reading the code(s) with a scan tool will help you diagnose the problem.

FUEL INJECTION IDLE SPEED CONTROL

Idle speed on fuel injected engines is computer controlled via an idle air bypass circuit on the throttle body. A small electric motor or solenoid is used to open and close the bypass orifice. The larger the opening, the greater the volume of air that can bypass the throttle plates and the faster the idle speed.

On newer vehicles with electronic throttle control, the computer also controls the opening of the throttle plate when the driver pushes down on the gas pedal. Position sensors in the gas pedal signal the computer how far to open the throttle plate.

Idle problems on EFI systems can be caused by varnish and dirt deposits in the throttle body idle control circuit. Cleaning the throttle body with throttle body cleaner can often solve idle problems (follow the directions on the product). Idle problems can also be caused by air leaks between the airflow sensor and throttle, the throttle body and intake manifold, and the intake manifold and cylinder head(s), or in the PCV or EGR systems, or vacuum hoses.

INJECTORS

A fuel injector is nothing more than a spring-loaded solenoid pintle valve. When energized by the computer, the solenoid pulls the valve open. This allows fuel to spray out of the nozzle and into the engine. When the computer cuts the circuit that powers the injector, the valve inside the injector snaps shut and fuel delivery stops.

The total amount of fuel delivered is controlled by cycling the injector voltage on and off very rapidly. The longer the pulse width, the greater the volume of fuel delivered and the richer the fuel mixture. Decreasing the duration of the injector signal pulse reduces the volume of fuel delivered and leans out the mixture.

Dirty fuel injectors are a common problem. A buildup of fuel varnish deposits inside the tip of the injector spray nozzle can restrict fuel delivery and interfere with the creation of a good spray pattern. This can cause a lean fuel condition and misfiring. Cleaning the injectors with fuel injection cleaner, or removing the injectors and having them cleaned on a fuel injector cleaning machine can usually restore normal operation. Using a Top Tier gasoline that contains adequate levels of injector cleaner can also prevent varnish deposits from forming.

FUEL PRESSURE CONTROL

Another important factor that helps determine how much fuel is delivered through an injector when it is pulsed, and that is the fuel pressure behind it. The higher the pressure behind the injector, the greater the volume of fuel that will spray out of the injector when it is opened.

Fuel pressure is generated by a high pressure electric fuel pump usually mounted inside or near the fuel tank. Pump output pressure may range anywhere from 8 to 80 lbs. depending on the application. The pump usually has an pressure valve to vent excess pressure and a check valve to maintain system pressure when the ignition is off.

In a multiport EFI system, the pressure differential between the fuel behind the injectors and the vacuum or pressure in the intake manifold is a constantly changing variable. Under light load or at idle, a relatively high vacuum exists in the intake manifold. This means less fuel pressure is needed to spray a given volume of fuel through the injector. Under heavy load, engine vacuum drops to near zero. Under these circumstances, more pressure is needed to deliver the same quantity of fuel through the injector. And in turbocharged engines, manifold vacuum can become 8 to 14 lbs. of positive pressure when turbo boost comes into play. Even more fuel pressure is required to force the same amount of fuel through the injector.

A means of regulating fuel pressure according to engine vacuum must be provided in a multiport EFI system to maintain the same relative pressure differential between the fuel system and intake manifold. This is done by the fuel pressure regulator. The regulator is mounted on the fuel rail that supplies the injectors. On returnless EFI systems, the regulator is part of the fuel pump assembly inside the fuel tank.

The fuel pressure regulator has a simple spring-controlled vacuum diaphragm with a vacuum connection to the intake manifold. The regulator decreases fuel pressure under light load and increases it under heavy load or boost conditions. The excess fuel pressure is shunted through a bypass port back to the fuel tank to maintain the desired pressure differential. Most systems are calibrated to maintain a pressure differential of somewhere between 40 and 55 psi.

On the older TBI systems, the regulator has an easier job because the injectors are mounted above the throttle plates. Since engine vacuum/boost has no effect on fuel delivery out of the injector on the TBI system, regulator only has to maintain an even pressure. On General Motors TBI applications, the pressure regulator is calibrated to maintain roughly 10 psi in the fuel system but most others run close to 40 psi.

Low fuel pressure will result in poor engine performance, possible misfiring and may prevent the engine from starting. Low fuel pressure can be caused by a weak fuel pump (a worn pump or low voltage to the pump that caused it to run slowly), restrictions in the fuel line, a plugged fuel filter, or a leaky fuel pressure regulator. Fuel pressure MUST be within specifications for the engine to run properly. Fuel pressure can be tested with a fuel pressure gauge connected to the service valve on the fuel rail, or teed into the fuel line.

Replace an Electric Fuel Pump

If an electric fuel pump is not working, is not delivering enough fuel pressure to meet specifications, or is not pumping enough fuel volume to keep up with the engine’s needs, the pump may need to be replaced. But before that happens, you should rule out all the other possibilities such as a plugged fuel filter, restricted fuel line, bad fuel pressure regulator, bad fuel pump relay, or fuel pump wiring problem. If all of these have been checked and eliminated, you can go ahead and replace the pump.

NOTE: The Fuel Pump Manufacturers Council says many fuel pumps are replaced unnecessarily or are returned under warranty because the fuel pump was not correctly diagnosed. So save yourself the time and trouble and make sure the pump is really bad before you buy a replacement pump.

In-Tank Electric Fuel Pump Replacement

The electric fuel tank on most vehicles with electronic fuel injection is located inside the fuel tank. If there is no access panel under the back seat or in the trunk of the vehicle, it means you will have to lower the fuel tank from the vehicle to replace the pump. This can be a difficult job, so you may want to take your vehicle to a service facility for repairs rather than trying to do it yourself.

WARNING: Gasoline is extremely flammable. Do not smoke when working on the fuel system, and keep any sparks or other sources of ignition away from the vehicle and fuel tank. Do NOT use an incandescent trouble light near the fuel tank as the hot surface of the light bulb can ignite any fuel that might spill or splash on it. Fuel vapors are heavier than air and can also travel a long distance along a garage floor. The fumes can be ignited by a heater, pilot light, electric motor or other source of ignition some distance away. Also be aware of the fact that static discharges can also ignite fuel. Proceed with caution.

Before you go to all the work of removing the fuel tank, double-check under the back seat and in the floor of the trunk for an access panel to the fuel tank. If the vehicle has one, you can change the pump without dropping the tank. Just skip the next couple of steps and undo the plate the holds the pump in the tank.

Before unbolting the straps that secure the fuel tank in place, remove as much fuel as possible from the tank. This will lighten the tank considerably and make it much easier to handle, lower and lift back into place. Some gas tanks have a drain plug in the bottom, but most do not so you will have to use a hand siphon pump to drain the tank (do NOT use an electric drill powered pump as the sparks may ignite the fuel!). Insert the hose down the filler neck and use the hand pump to start the siphon action. Do NOT suck on the hose to start a siphon because gasoline is poisonous and the fumes can harm your lungs. Drain the fuel into an approved container (a metal or plastic gas can, NEVER an open bucket), and seal the container once all the fuel has been drained from the tank. Do NOT leave open containers of gasoline sitting around.

How to Replace an In-Tank Electric Fuel Pump

Set the parking brake and place the transmission or transaxle in park (in gear if it is a manual transmission). Also, block the front wheels so the vehicle can’t roll when you raise the rear wheels off the ground. The vehicle should also be parked on a level surface.

Raise the rear of the vehicle as needed with a jack, and support the vehicle with a minimum of TWO jack stands (make sure the stands have the proper weight rating to handle the weight of the vehicle). NEVER crawl under a vehicle that is only supported by a jack.

Disconnect the filler neck from the fuel tank by loosening or removing the clamp that holds the hose on the tank.

Remove either the front two bolts or the rear two bolts that secure the fuel tank straps to the vehicle. Then gently lower one end of the tank. This will allow you to reach the wiring connections, fuel line and vent hoses on top of the tank. Disconnect the wires and hoses before removing the two remaining bolts that hold the other end of the straps. The tank can now be lowered from the vehicle.

remove fuel pump from tank
Removing the cover plate to replace the fuel pump inside the tank.
Once the tank is sitting on the ground, you can undo the plate on the top of the tank the holds the fuel pump in place. The plate may have a metal ring that has to be rotated counterclockwise to remove the ring. Or, the plate may be held in place with screws or bolts. Once this plate has been loosened, the plate, fuel pump and sending unit can be carefully pulled out of the tank.

Get the Correct Replacement Pump

Once you have removed the old ful pump from the tank, you can buy a replacement pump online or from your local auto parts store. Make sure you get the correct replacement fuel pump for your vehicle. Many pumps appear similar on the outside but may have different flow rates and pressure ratings.

On some applications such as GM Flex Fuel vehicles and others, the engine VIN code may be necessary in addition to the year, make and model to look up the correct replacement pump.

Some replacement pumps may not look exactly the same as the original. That’s because some older vane and georotor style fuel pumps have been discontinued and replaced with newer, more efficient turbine style fuel pumps. Turbine pumps are better because they use less amperage, spin faster and provide longer life and quieter operation.

We would also recommend buying a name brand electric fuel pump rather than Made-in-China pump. The cheap Chinese pumps have a poor reputation for quality and durability, and may fail at low mileage.

Another piece of advice is to replace the whole fuel pump module assembly rather than just the pump itself. Yes, it costs more to buy a module than a bare pump, but the module makes installation a LOT easier and it reduces the potential for additional trouble later. On older high mileage vehicles, the plated metal electrical contacts on the fuel sender unit lever arm are often worn or corroded, affecting the units ability to send an accurate fuel level signal. Also, on newer vehicles with returnless EFI systems, the module also has the fuel filter built into it (which may or may not be available separately). A new sending unit and filter come preinstalled with a new fuel pump module assembly, along with new wiring.

On some newer vehicles with returnless EFI systems, you can’t even buy the fuel pump separately. You have to replace the entire fuel pump module.

Pump and Tank Inspection

Clues as to why the pump failed may be found by examining the filter screen on the pump inlet, and peering into the tank itself. If the filter screen is clogged with dirt or rust, the fuel tank will probably need to be cleaned or replaced. Dirt can be removed by steam cleaning or pressure cleaning the inside of the tank and allowing it to dry. If the fuel that was drained from the tank is dirty, it should be disposed of or run through a coffee filter before it is reused. If the tank is steel and it is rusty inside, you should replace it with a new one. Nothing will kill a new fuel pump faster than installing it inside a dirty tank. The gas tank should be replaced if it is leaking.

new fuel tank
Swapping hoses from an old fuel tank to a new one.
Inspect the wiring harness that connects to the old fuel pump. Loose, corroded or damaged connectors or wires can create excessive resistance that will reduce current to the pump and cause it to run slowly or not at all. Fix any wiring faults that need repair BEFORE you install the new pump.

When you install the pump in the tank, put a new filter screen on the pump (a new screen usually comes with the pump). If you are replacing the entire fuel pump module assembly, it will come complete with a new inlet filter screen and fuel level sending unit.

A new gasket or seal should also be installed on the top plate to prevent leaks.

Inspect the fuel and vent hoses. If any of the hoses are cracked, leaking or damaged, replace them with new hoses. For fuel hoses, be sure to use high pressure hose that approved for EFI use (not carburetor or vapor hose which lacks an adequate pressure rating). New hose clamps are also recommended.

fuel pump inlet filter
Never reuse an old filter screen. Install a new screen on the new pump before it goes into the tank.

Once the pump has been installed in the tank, reinstall the fasteners or locking ring that holds the pump cover to the fuel tank. Reconnect the wiring harness to the pump, making sure all the connectors are clean and tight. You can use dielectric grease on the connectors to keep out moisture that could cause corrosion later on.

Reconnect the EVAP system vapor hoses to the fuel tank, and the fuel line to the fuel pump outlet. Make sure all hoses are correctly routed.

Raise the fuel tank back into place and reinstall the support straps that hold it in place.

Reconnect the fuel filler hose to the fuel tank inlet. Make sure all clamps are tight.

Add several gallons of fuel to the tank and check for leaks. The tank should be at least 1/4 full to provide enough fuel for proper fuel pump lubrication and cooling before starting the vehicle.

Important Warning Lights You Should Never Ignore

If any of the above warning lights come on while you are driving, DO NOT IGNORE THEM! Immediate action may be necessary to prevent damage to your vehicle, a breakdown or an accident.

OIL PRESSURE WARNING LIGHT

The oil pressure warning light comes on if your engine has lost oil pressure or oil pressure is too low for safe engine operation. You should pull over to the side of the road, shut the engine off and check the oil level on the engine dipstick.

Possible Causes: Low oil level (due to oil consumption or leaks), oil viscosity too thin, worn oil pump, excessive engine bearing clearances or defective oil pressure sending unit.

If you engine is also making ticking, clattering or rapping noises, it is not getting sufficient oil. If you attempt to drive the engine in this condition, you will probably damage it – if it hasn’t already suffered major internal damage.

TEMPERATURE WARNING LIGHT

The temperature warning light will come on if your engine is overheating. Do NOT continue driving if your engine is overheating as this can cause expensive engine damage (piston scuffing, valve stem galling, failed head gasket, cracks or distortion in cylinder head). Stop driving, pull over and shut your engine off. Open the hood and check the radiator and heater hoses, radiator and engine for coolant leaks. Note the level of the coolant in the coolant reservoir.

CAUTION: DO NOT open the coolant reservoir or radiator cap until the engine has cooled off for at least 30 minutes. Steam pressure inside the cooling system can blow out and burn you!

If the coolant level is low, add coolant (a 50/50 mixture of antifreeze and clean distilled water) after the engine has cooled down.

Possible Causes: Low coolant level (due to coolant leak or bad head gasket), stuck thermostat, bad water pump, broken serpentine belt, defective radiator cooling fan, clogged or dirty radiator, exhaust restriction (plugged catalytic converter).

HINT: Turning the A/C OFF and turning the heater on HIGH may help cool down an engine that is temporarily overheating due to unusually hot weather or from towing a trailer. But if the engine is running hot because it is low on coolant, this trick probably won’t help much.

CHARGING SYSTEM WARNING LIGHT

The “GEN” or “ALT” warning light, or an icon of a battery will illuminate if the charging voltage in your vehicle is low. You do not have to stop immediately, but you may only have 20 to 30 minutes of driving time before your battery goes dead and your engine stops running (or even less time if you are driving at night with your headlights on).

Possible Causes: Broken or slipping serpentine belt or V-belt, bad alternator, charging control fault, or loose or corroded battery cables.

Open the hood to see if the drive belt that turns the alternator is intact and is turning the alternator while the engine is idling. If the belt is not the problem, chances are the charging system has a problem that will have to be diagnosed and repaired. Better find a repair shop soon!

BRAKE WARNING LIGHT

The Brake Warning light will come on if the parking brake has not been fully released, but it may also come on if the brake fluid level is low or there has been a loss of hydraulic pressure in one of your car’s brake circuits. Loss of fluid or brake pressure means the brakes may not be able to stop your car when you step on the pedal.

Carefully apply the brakes to see if they are working. If they are, pull over to the side of the road, open the hood and check the fluid level in the brake master cylinder. If the fluid level is low, the brake system should be inspected for leaks. If there are leaks, your brake system is unsafe to drive.

If the brake pedal is low or goes to the floor, pumping the pedal may apply enough pressure to stop your car. If that fails, apply your parking brake to slow your vehicle. Also, take your foot off the gas and shift to neutral, or downshift and use engine braking to slow your vehicle if you have a manual transmission. If all that fails, aim for something soft like a bush or open field.

Possible Causes: Loss of brake fluid due to leaks (master cylinder, calipers, wheel cylinders, brake lines or hoses), failure of the pressure differential switch that activates the brake light, parking brake pedal or handle not fully releasing, defective parking brake switch.

WARNING: If the brake pedal feels soft, is low, goes to the floor, or you have to pump the pedal to get your vehicle to stop, your vehicle is unsafe to drive. You should have it towed to a repair facility for repairs.

LOW TIRE WARNING LIGHT

low tire pressure warning light The Low Tire Pressure Warning Light will come on if any tire on your vehicle is 25 percent or more underinflated. Driving on a low tire can be dangerous because it increases the risk of a tire blowout. A low tire can also cause uneven braking, uneven traction, uneven and rapid tire wear, increased rolling resistance and fuel consumption.

Find a gas station with an air pump, and check the inflation pressure in each tire with an accurate gauge (not the gauge on the pump, which is often very inaccurate!). Add air as needed to inflate your tires to the recommended pressure (see your owners manual or the tire inflation decal in teh door jam or glove box). For most passenger cars, the recommended pressure is typically 32 to 34 PSI.