Fuel System Diagnosis

FUEL SYSTEM DIAGNOSIS

SYSTEM DESCRIPTION
When you turn ON ignition switch, the control module 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 control module receives ignition reference pulses. If there are no ignition reference pulses, the control module shuts the fuel pump OFF within 2 seconds after the ignition was switched to the ON position, or if the engine stops.

The fuel pump is an electric pump that is attached to the primary fuel tank module assembly. The fuel pump also supplies fuel to the siphon jet pump, also attached to the primary fuel tank module. The siphon jet pump draws fuel from the secondary side of the fuel tank to the primary 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. Unused fuel is returned to the fuel tank by a separate fuel return pipe. A fuel pressure regulator, which is located on the fuel rail assembly, 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.

TEST DESCRIPTION

Steps 1-4:

Steps 5-6:

Steps 7-9:

Steps 10-11:

Steps 12-15:

Steps 16-17:

Steps 18-22:

Steps 23-27:

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 inspects the fuel pressure regulator for a fuel leak from the atmospheric vent. If fuel leaks from the fuel pressure regulator while the fuel pump is commanded ON, replace the fuel pressure regulator.
11. This step tests for a loss of fuel pressure between the shut-off adapter on the fuel feed pipe and the fuel pump.
12. This step tests for a leaking fuel injector or fuel pressure regulator. If the fuel pressure remains constant during this test, the fuel injectors are not leaking fuel.
15. This step tests for a restricted fuel return pipe. If the fuel pressure is within the specified values, a restriction in the fuel return pipe is indicated.
17. This step determines if the fuel pressure regulator, or the fuel pump, is the cause of the low fuel pressure. If the pressure rises above the specified value, the fuel pump is OK.
21. This step verifies that a circuit condition is not the cause of a fuel pressure concern. Inspect all fuel pump electrical circuits thoroughly.