Fuel Pump Testing

CIRCUIT DESCRIPTION
When you turn ON the ignition switch, the control module enables the fuel pump relay which powers the fuel pump ON. 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 in-tank fuel pump is an electric pump that is attached to the fuel sender assembly. The fuel pump also supplies fuel to the right fuel tank siphon jet pump. The siphon jet pump transfers fuel from the right fuel tank to the left 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 part of the fuel filter assembly, keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel is returned to the fuel tank by a separate fuel return pipe.

TEST DESCRIPTION

Steps 1-5:

Steps 6-10:

Steps 11-14:

Steps 15-19:

Steps 20-29:

2. This step verifies that the fuel pump is operating.
4. This step verifies that the vehicle is not out of fuel. If the left fuel tank is empty, and there is fuel in the right fuel tank, 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 tests for a loss of fuel pressure between the fuel feed pipe shut off adapter and the fuel injectors. If the fuel pressure decreases during this test inspect for a leaking fuel injector.
11. This step tests for a loss of fuel pressure between the fuel feed pipe shut off adapter and the fuel pump. If the fuel pressure remains constant with the shut Off valve closed, the loss of fuel pressure is caused by the fuel pump.
12. This step tests if the loss of fuel pressure is caused by the fuel pressure regulator, or by the check valve that is located in the fuel feed rear pipe.
15. 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.
16. This step verifies that there is an adequate supply of fuel to the siphon jet pump.
17. This step verifies the fuel return from the siphon jet pump. If the fuel returned is near the specified value, inspect the left fuel sender for blockage.
20. This step verifies that a circuit condition is not the cause of a fuel pressure concern. Inspect all fuel pump electrical circuits thoroughly.