Symptoms of a failing fuel pump

By YOUCANIC on Aug 19, 2019

Symptoms of a failing fuel pump

The fuel system is one of the most important systems in the vehicle. Without the fuel system, the vehicle will not run.

When a car randomly dies there is a good chance your fuel pump is on its way out.

There are a few ways to check that you have a fuel system problem.

Symptoms of a failing fuel pump

  • car won't start
  • engine stalling,
  • fuel in the vacuum hose,
  • dipstick smells like fuel,
  • excessive black smoke from the tailpipe,
  • poor running engine,
  • blackened spark plugs.

If any of the sign is shown above, replace the fuel pressure regulator. In addition, make sure to inspect the vacuum hose going to the fuel pressure regulator.

Next, check the fuel filter. A clogged fuel filter will prevent fuel from entering the engine; It may also decrease fuel pressure. We also recommend replacing the fuel filter as part of regular maintenance.

Signs your fuel pump is failing

There are a few signs that a fuel pump is on its way out.

First, a whining noise can be heard coming from the fuel tank. Furthermore, your vehicle may experience performance problems.

For example, there may be a misfire due to low fuel pressure. Your car may also die when you step on the gas pedal. That means fuel is not keeping up with demand. Moreover, Your car may also hesitate when giving it gas.

This problem can be caused by a bad fuel pump but also due to a clogged catalytic converter.

Troubleshooting a bad fuel pump

The car will not start

First thing you should do check is for a humming noise coming from the fuel pump. The humming noise comes from the motor in the fuel pump.

The fuel pump is located in the fuel tank which is located in the back of the vehicle. Turn the key to on position and turn off your radio. You will listen for a humming noise. The fuel pump will prime for 2 seconds then turn off.

At this point, you should be able to hear the fuel pump run. If you do not hear the fuel pump humming go step #2.

Crankshaft Position Sensor

Note that a bad crankshaft position sensor may exhibit similar symptoms where car will not start. When the CPS fails you often will have a hard time starting the car when the engine is hot. 

Check fuel pressure

symptoms of bad fuel pump

There are a few ways to check for fuel pressure. For this step you will need a fuel pressure test kit. 

First, locate the shredder valve located on the fuel pressure rail.

Connect a fuel pressure gauge to the fuel pressure shredder valve. Turn the key to on position.

car wont start due to a bad fuel pump

This will activate the fuel pump. If there is fuel pressure the fuel pump is functioning properly. Check the fuel pressure specification online or use your manual that came with your car.

fuel pressure test

Most fuel pressure on a car run between 35-55 psi. If you do not have a fuel pressure gauge, you can simply get a screwdriver and push down the pin on the shredder valve. Some fuel should be released. Be mindful not to get fuel in your eyes. Maintain distance. If there is no fuel pressure, go to step #3.

Check fuses

Use a digital multimeter to check for a blown fuel pump fuse. Located the fuse box. Usually, it is mounted in the engine bay by the side or sometimes underneath the steering wheel.

Check the fuse by using a test light. Put the test light on the negative side of the battery and touch the terminal on top of the fuse.

The test light should light up on both sides on top of the fuse. If the test light does not light up, remove the fuse and inspect it. If it is blown, replace it. Next, check the relay.

Check fuel pump relay

Fuel pump relay may have failed in which case no power is sent to the fuel pump. Checking the fuel pump relay is a simple procedure which you can perform using a digital multimeter

Fuel pump relays are usually four posts and very inexpensive to replace. 

Check for power at the fuel pump

The next step would be to check for power at the fuel pump. Unplug the wire harness from the fuel pump.

Connect a digital multimeter to the plug and turn on the ignition. You should read 12-14 volts at the fuel pump. 

Read Codes

If you have a code reader read the fault codes from the ECU. A current diagnostic trouble code or even stored codes can help you figure out why the engine won't start.

Read this guide, to learn more about OBD2 scanners.

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