How To Relieve Fuel Pressure

by Dan Ferrell

Relieving the fuel system pressure on your vehicle is very important when working on the fuel pump, fuel injectors, lines and other related components. That system, especially on fuel-injectede models, operates under high pressure and remains like that even when you shut off the engine. Different vehicle manufacturers have devised several methods of relieving fuel pressure. Here, we will cover five of the most common systems so you can work safely on your own vehicle.

Relieving Pressure with the Fuel Pressure Regulator

Disconnect the negative battery cable using a wrench. This will prevent sparks, which could ignite fuel and fuel vapors.

Locate the fuel pressure regulator on the fuel rail. The rail is mounted along the top area of the engine. Make sure the regulator is vacuum operated.

With your hand, remove the vacuum hose from the top of the fuel pressure regulator.

Connect a hand-operated vacuum pump to the top of the pressure regulator.

Apply about 16-inches Hg of vacuum to the regulator to push the fuel in the lines back into the fuel tank.

Relieving Pressure with the Fuel Pump Connector

Access the sending unit/fuel pump assembly on top of the fuel tank. Some vehicle models provide an access door to the fuel tank through the floor underneath the rear seat or under the trim in the trunk. On other models, you will have to raise the rear of your vehicle using a floor jack and support it on two jack stands to access the sending unit/pump assembly.

If there your model has an access door above the tank, either remove the rear seat by pulling the retaining strap on the back of the seat and lifting it, or remove the trim on the floor of the trunk (again, the location of the access door varies by model). Remove the mounting screws on the fuel tank access door using a Phillips screwdriver or pulling the butyl tape around the door.

If the fuel pump is accessed from underneath, be sure the vehicle is secured on the jack stands before crawling underneath and locating the fuel pump assembly.

Unplug the fuel pump electrical connector on the sending unit/pump assembly.

Start the engine and let it idle until it stalls. Then turn off the ignition switch.

Disconnect the negative battery cable.

Relieving Pressure with the Fuel Pump Fuse and Relay

Locate the fuel pump fuse under the dashboard or in the engine compartment. It is usually located on the driver's side of the vehicle. In most cases, it is marked for easy identification. Your owner's manual will tell you where to find the fuel pump fuse.

Remove the fuse with your hand or a pair of pliers. Or remove the fuel pump relay with your hand.

Start the engine and let it idle until it stalls.

Disconnect the negative, battery cable using a wrench.

Relieving Pressure with the Ford Inertia Switch

Search for the inertia switch around the trunk, rear compartment or under the dashboard. Many Ford models use this shut-off switch to cut off fuel to the system in case of an accident. Consult your owner's manual if necessary.

Unplug the inertia-switch's electrical connector.

Start the engine and let it run until it stalls.

Disconnect the negative battery cable.

Relieving Pressure with the Test-Port Valve

Disconnect the negative battery cable. Search for the Schrader valve on the fuel rail around the top of the engine, if your vehicle is equipped with fuel injection system. Some models use this valve for test purposes. This valve looks like the air valve on a bicycle tires.

Unscrew the valve cap if there is one.

Wrap one or more shop rags around the port valve to catch the squirt of fuel that will come out as you depressurize the system.

Push the valve in using a small screwdriver until fuel stops pouring through the valve.

Replace the test-port valve cap.

Tip

  • check If you need help locating some components on your vehicle, consult your owner's manual or a vehicle service manual. You can consult one at most public libraries or buy one at your local auto parts store.

Warning

  • close Always loosen or remove the fuel filler cap on your vehicle when you are working on the fuel tank. That will relieve pressure build-up in the tank. Always disconnect the negative battery cable when working the fuel system of a car.

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About the Author

Since 2003 Dan Ferrell has contributed general and consumer-oriented news to television and the Web. His work has appeared in Texas, New Mexico and Miami and on various websites. Ferrell is a certified automation and control technician from the Advanced Technology Center in El Paso, Texas.

Photo Credits

  • photo_camera Photo courtesy of Ian Brockhoff from Wikipedia.org.