Bad Fuel Pump Symptoms to Watch Out For

Learn the most common symptoms of a bad fuel pump

When a fuel pump begins to fail, it can lead to a variety of issues that can affect the performance and reliability of your vehicle. Recognizing the symptoms of a bad fuel pump early can prevent further damage and costly repairs. Here are some common symptoms to watch for:

The Top 8 Bad Fuel Pump Symptoms

1) Your engine won’t start— You turn the key, and the engine cranks and doesn’t start, no matter how long you crank the engine. The test for this is a fuel pressure and volume test. If it’s not outputting the correct pressure or volume, replace the pump. Or, if your vehicle has a fuel pump driver module, test that before condemning the pump.

2) You have to crank the engine for a long time before it finally starts— Extended cranking on cold starts is often a sign of a failed check valve located in the fuel pump. The check valve prevents fuel pressure from draining back into the tank after the engine shuts down. It also maintains close to full fuel

This image shows a typical turbine-style fuel pump. Notice the one-way check valve on the exit side of the pump

pressure in the fuel rail to provide rapid starts.

A drop in fuel pressure in excess of 5 psi. overnight is often a sign that the check valve has failed. When the pressure falls, the fuel pump must refill the fuel rail and build adequate fuel pressure to work the fuel injectors. That requires the fuel pump to run for longer periods and results in extended cranking. The check valve is located in the fuel pump and cannot be replaced separately.

The most reliable test for a check valve is to do a leak-down test. The technician attaches the fuel pressure gauge to the fuel rail and starts the engine. Then, the engine is shut down and left overnight. The technician checks fuel pressure the next morning and records the pressure reading. Generally, a drop of more than 5-psi. means the check valve has failed. However, often, the technician will see a total loss of fuel pressure due to a leaking check valve.

3) The engine doesn’t restart after being run for a long period— After running for a long time, an overheated fuel pump may not produce enough pressure to start the engine. However, if you let it sit for a few hours, and it starts, that’s a sign of a bad fuel pump.

4) The fuel pump makes a loud whine when the key is turned to the RUN position— A good fuel pump makes a slight humming sound while it’s priming the fuel rail at startup. However, a loud whining sound from the fuel pump indicates a more serious

The fuel pump module housing contains the fuel pump, pulsator and fuel pressure regulator, filter sock, fuel level sensor, float and float arm, inlet and outlet connections, and springs to keep the unit at the bottom of the tank

problem. The loud whine can be caused by a clogged in-tank filter, a clogged fuel filter, or a bad fuel pressure regulator or pulsator. A pulsator is a noise-reduction device that dampens the vibrations created while pumping.

5) The engine lacks power, hesitates, or stalls while driving— The fuel pump must deliver the proper pressure and fuel volume to match the requested engine load and speed. A failing fuel pump might deliver the proper fuel pressure but not the correct volume, and vice versa.

6) Intermittent no-start— This is the toughest symptom to diagnose since it happens intermittently. In this case, the shop may request that you leave the vehicle for several days so the technician can attach test equipment and drive it until they duplicate the problem.

7) Surging can be a bad fuel pump symptom— In this case, the fuel pump can’t keep up with the demands of the engine, so the engine surges. To diagnose, conduct both a fuel pressure and fuel volume test to see if the pump can output the proper amount of fuel.

9) Rising engine temperature and P0171 or P0171 trouble code— When a fuel pump can’t deliver the right fuel pressure and volume, the engine experiences lean misfires. In other words, there’s not enough fuel for complete combustion. Lean misfires cause the engine to run hotter than normal, so you can see a rise in engine temperature. A failing fuel pump can cause a P0171 or P0172 trouble code. Both codes indicate a lean condition. Lean codes mean your engine is either getting too much air or too little fuel.

If you have any of these bad fuel pump symptoms, here are the most common tests to confirm the problem

• Fuel pump pressure test
• Fuel pump volume test
• Fuel pump leak down test
• Test the fuel pump wiring for high voltage drops or poor ground connections
• Test for proper fuel pump driver operation (if equipped)

See this post for tips on how to troubleshoot a fuel pump

©, 2017 Rick Muscoplat