How to Depressurize a Fuel System

by Thomas West

Modern automobiles and trucks use a fuel injection system to deliver the correct air and fuel mixture to be burned in the engine cylinders. The fuel injection system operates under high pressure, therefore before any maintenance work is to be done on the fuel system, such as replacement of the fuel filter, the fuel system must be depressurized. Depressurizing the fuel system will keep you from getting a dangerous spray of fuel on you when you remove the fuel filter.

Step 1

Loosen the fuel filler cap on the outside of your vehicle without removing it. Listen for the audible hiss to subside, telling you that the pressure in the fuel tank has been released.

Step 2

Locate the fuel lines that attach to your fuel filter. Note that in some vehicles the fuel filter is mounted underneath the vehicle on a frame rail, while in other vehicles the filter is located in the engine compartment. Check your owner's manual for the location of your fuel filter. Loosen the fittings of the fuel lines on the filter by turning them with a flare wrench in a counterclockwise direction, but do not remove the fittings completely.

Step 3

Wait several minutes for the pressure in the lines to release. Note that fuel will leak from the cracked-open fittings until the pressure is released. Clean up any spills with rags.

Step 4

Remove the fuel lines from the fuel filter if the filter is being replaced, otherwise leave them loosened until your maintenance work is complete. Tighten the fuel lines in a clockwise direction once your maintenance work has been completed and you wish to pressurize the fuel system again.

Step 5

Tighten the fuel filler cap.

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