The fuel pump runs continuously while your engine is running, delivering high-pressure fuel, to the fuel rail and injectors.
The fuel pump keeps cool by staying submerged in fuel, or else it would overheat.
So, if you make a habit of running your tank all the way to empty, before filling up. Then, your fuel pump will most likely die, before its designed lifespan.
So, the symptoms of a bad fuel pump, can be other issues as well. Such as, bad fuel, damaged fuel lines or a clogged fuel filter.
So, what if your engine was running fine with no hints of trouble. Then, you find it just will not restart:
- Maybe you stopped to fill the gas tank and the engine will not restart.
- You have been shopping and when you returned to the car, the engine will crank over, but will not restart.
Is Your Fuel Pump Working ? Let’s Start With Some Basic Testing:
- Turn off the radio and close the windows, to eliminate any noise in the car.
- Next, turn the key, so the gauges and warning lights come to life, but don’t start the engine.
- You should hear a buzzing sound, when you turn on the key.
- This sound could be, from under the car or in the back near the trunk.
The buzzing sound you are listening for, sounds like an electric motor running. This sound is the electric fuel pump trying to prime the fuel system. It will only run for a few seconds, and then shut off. If you are not sure you could hear it, or if there is noise outside. Then, you may have to try it several times.
Turn the key on and wait, then turn it off. If there is no noise outside of the car you may need to try this, with the car door open. So you can hear, under the car. Keep doing this, until you have confirmed if it works.
Many people recognize this sound every time they start the car, but don’t realize it is the fuel pump running.
If you “DO NOT” hear the buzz of the fuel pump, then your engine has no fuel pressure, and we need to see why.
How To Determine If Your Fuel Pump Has Failed
The first thing you want to do is check the fuse panel, to see if the fuse is blown. If your car has two fuse panels, than the one in the engine compartment, should be checked first. The fuse panel or circuit box, is usually located near the battery. And, is a small black box, with a removable lid.
Inside the cover, you can find the fuse index, if provided. Many manufacturers list the fuses by number, and position inside the lid. However, if your car does not list them, you will have to check your owner manual.
Pull out the fuse and hold it up, to see if the element if broken. If so, you can replace it. Some fuse boxes supply extra fuses that you can use. Just make sure you use the same color fuse, or one with the same AMP number listed on the top.
If the fuse is good, then you will need to check the fuel pump relay.
You can find the relay, in the same circuit box. Without proper test equipment, you won’t be able to test the relay. But, many of the relays in the box, are the same AMP rating and size. If you switch the relay with a different one, of the same size and rating. ( same amount of prongs on the bottom ). Than, you can try to start the car, or listen for the fuel pump to run, with the key on.
This will let you know, if your relay is bad. If this test works and the fuel pump runs, just replace the bad relay, before you drive the car.
Fuel Pump Circuit Breaker Reset
Some cars have a fuel pump circuit breaker, instead of a fuse. If you cannot find a fuel pump fuse, then check your owner’s manual for its location. Breakers, usually have a button on top that pops up when it trips. Simply push this button back, in until it clicks. Check the owner’s manual for the exact location.
Automatic Shutdown (ASD) Relay
One of the most common symptoms of a bad (ASD) relay, is an engine that will start. But, stalls almost immediately, or at random times. The (ASD) relay supplies power to the vehicle’s, ignition coils and fuel injectors. Certainly, the most important components, of the entire engine management system.
Fuel Pump Testing
If the fuse is good and the circuit breaker is not tripped, then the engine is not getting fuel pressure.
At this point many mechanics will open the rubber boot at the throttle body, and spray a small amount of starter fluid into the manifold, reinstall the boot and try to start the engine. In most cases, the engine will start and run for a second or two, then shut down.
This verifies that, if the engine were getting gas, it would start correctly. This also verifies that, the engine has no fuel pressure.
Electric fuel pumps on electronically controlled fuel injection systems, need to produce a “high” pressure. Consequently, to allow the injectors to produce, a sufficient spray of atomized fuel, into the intake path. (or into the combustion chamber in a direct-injection system). Fuel pressure is typically, in the 35 to 45 psi range.
Anti-Theft System Issue
If your Anti-Theft light is flashing, the anti-theft system is disabling the fuel pump, to prevent the engine from starting.
The problem could be:
- A defective chip in a smart key.
- Dead battery in a smart key or keyless entry fob.
- A fault in the Anti-Theft system itself.
Fuel Pump Testing Checklist
- Bad fuel pump. (Pump should run for a few seconds, when ignition key is turned to start. However, no buzz means no fuel delivery to the engine).
- Blown fuel pump relay. (Relay is energized by the (PCM), to route power to fuel pump when ignition is on).
- Bad inertia fuel shut-off safety switch. (Shuts off fuel in an accident, may have been tripped by a severe jolt, press button to reset).
- Open in wiring anywhere in the wiring circuit. (power or ground). Problem may be at wiring connector on top of fuel tank (hard to reach!).
- No gas in fuel tank. (Check the fuel gauge, and keep in mind the gauge may not be reading accurately).
- Bad gas (Contaminated with water or too much alcohol or diesel fuel). If you just filled up with gas and now your car won’t start, suspect bad gas.
- Plugged Fuel Filter. (When was the filter last changed?). Replace the filter.
- Plugged or Pinched Fuel Line. (Inspect fuel lines under vehicle for damage).
- Leaky Fuel Pressure Regulator. (Controls fuel pressure to the injectors, which is critical for starting and proper air/fuel mixture).
- No power to Fuel Injectors. (Due to faulty fuel injector relay, blown fuse. No input signal to the (PCM) from crank position sensor or cam position sensor, or bad (PCM) driver circuit). Injectors should usually have power, when the key is on. (PCM) grounds other side of injector circuit, to pulse the injectors.
- Major vacuum leak. (An open (EGR) valve, disconnected vacuum hose, (PCV) valve, can create a large vacuum leak. And, allow too much air to be sucked into the engine. This will make the air/fuel mixture too lean, and make the engine hard to start. Engine will usually idle rough, if it does start.
Proper Care Will Prevent A Fuel Pump From Failing Prematurely
Electric fuel pumps run continuously with your engine, delivering high-pressure fuel to the fuel rail and injectors. Fuel pumps keep cool, by staying submerged in fuel. If you make a habit of running your tank all the way to empty, before filling up. Then, your fuel pump will most likely die, before its designed lifespan.
This is due to the fact that, when you shut off the engine with a low fuel level, the fuel can drain from the priming chamber designed into the fuel delivery system.
So, when you restart your car, the pump runs hot and un-primed, until it can refill the fuel chamber. Over time, this will burn out the pump motor. This is why many pumps fail, right after shutting off the car and restarting it, while it is hot. Like when you stop to refill the tank with gas.
Conclusion
To prolong the life of your fuel pump, don’t let your fuel level drop, below an eighth of a tank. Finally, this will prevent the pump from losing its prime, and keep the pump motor cool.
BY DANNY BENDER
