Fuel System Diagnosis

FUEL SYSTEM DIAGNOSIS

SYSTEM DESCRIPTION
When you turn the ignition switch to the ON position, the engine control module (ECM) enables the fuel pump relay, which in turn powers the fuel pump. The fuel pump remains ON as long as the engine is cranking or running and the ECM receives ignition reference pulses. If there are no ignition reference pulses, the ECM shuts the fuel pump OFF within 2 seconds after the ignition was switched to the ON position, or if the engine stops.

The fuel tank stores the fuel supply. The fuel pump is an electric pump that is attached to the right fuel tank module assembly. The fuel pump also supplies fuel to the siphon jet pump, also attached to the right fuel tank module. The siphon jet pump draws fuel from the left side of the fuel tank to the right side of the fuel tank. The fuel pump is designed to provide fuel at a pressure above the pressure that is needed by the fuel injectors. A fuel pressure regulator, which is also located in the fuel tank, is attached to the right fuel tank module. The fuel pressure regulator keeps the fuel available to the fuel injectors at a regulated pressure. The port on the fuel pressure regulator is an atmospheric vent. The fuel pressure regulator does not compensate for changes in intake manifold vacuum. Unused fuel is returned from the fuel filter to the fuel tank by a separate fuel return pipe.

TEST DESCRIPTION

Steps 1-5:

Steps 6-7:

Steps 8-9:

Steps 10-12:

Step 13:

Steps 14-16:

Steps 17-20:

The numbers below refer to the step numbers on the diagnostic table.
2. This step verifies that the fuel pump is operating.
4. This step verifies that the vehicle is not out of fuel. If the right fuel sender is below 0.8 V, and the left fuel sender is above 0.8 V, a fuel transfer condition exists.
7. This step tests for an internal fuel leak. If the fuel pressure drops during this test, then an internal loss of pressure is indicated.
10. This step isolates the condition. Replace the primary fuel tank module assembly, if the fuel pressure remains constant, after closing the valve on the fuel pipe shut-off adapter. Locate and replace the leaking fuel injector if the pressure continues to decrease after closing the valve on the adapter.
13. This step isolates the condition. Replace the primary fuel tank module assembly for a stuck open or leaking fuel pressure regulator, if the fuel pressure increases above the specified value.
16. This step verifies that a circuit condition is not the cause of a fuel pressure concern. Inspect all fuel pump electrical circuits thoroughly.