How to Troubleshoot a Fuel Pump Pressure


Most of the time when the fuel pump in your car gives you trouble, it is due to low pressure or pump gas leakage because of worn-out components. You will notice the symptoms most when running at highway speeds--since the fuel pump will not be able to deliver the extra fuel--or you just will not be able to start the engine due to a dead pump. But in order to verify that your fuel pump is out of order you need to test the system and isolate the fuel pump. Here we will work with two of the most common systems--electronic fuel injection (EFI) and throttle body injection (TBI)--going through some simple steps to confirm that the fuel pump has reached the end of its service life and needs to be replaced.

Things You'll Need

  • Fuel pressure gauge
  • 2 to 3 inches jumper wire
  • Hose clamping tool
  • Locate the threaded Schrader valve or test fuel pressure port. This valve is very similar to those used on automobile and bicycle tires. You may find it on the fuel rail or near the fuel pressure regulator.

  • Determine what type of fuel line disconnect--the rubber hose to metal line connector close to the fuel rail or TBI unit--your system is equipped with if it does not have a Schrader valve or your engine has a TBI system: spring-lock, pinch, clamps, threaded or quick-connect fitting. Fuel line connector couplings differ according to manufacturer. If necessary, consult the service manual for your particular vehicle.

  • Relieve the system fuel pressure.

  • Connect a fuel pressure gauge to the Schrader valve or fuel inlet line according to the gauge manufacturer.

  • Locate the fuel pump relay and remove it. Install a small jumper wire in the relay connector to activate the fuel pump and turn the ignition switch on but do not start the engine. Record the fuel pressure reading from the gauge. Turn the ignition off and reinstall the fuel pump relay.

  • Start the engine and record the reading from the pressure gauge. Turn off the engine.

  • Pinch the fuel return line with a hose clamping tool or wrap the fuel line with a rag and pinch the hose with a pair of pliers to isolate the pump from the fuel system.

  • Start the engine and record the reading from the pressure gauge before the engine stalls. This reading should be almost twice as much as the one from the previous test and it will tell you if the fuel pump can deliver the correct pressure under operating conditions.

  • Compare the tests readings to the specifications given in your vehicle service manual. If any of the readings is out of specification, check that filter, hoses and lines in the fuel system are in good condition and there are no gas leaks before deciding to replace the fuel pump.

Tips & Warnings

  • If a pressure gauge is somehow expensive for your current budget, you may be able to rent one in a major auto parts or equipment rental store.
  • Use the service manual for your particular vehicle to locate, identify and obtain components’ operating specifications. You can buy a vehicle service manual at most auto parts stores or consult one for free at most public libraries.
  • When working on your vehicle's fuel system, make sure you are in a well ventilated area, away from appliances with open flames like dryers or water heaters and do not allow smoking near your vehicle.

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