Fuel Pump Electrical Circuit Diagnosis

Fuel Pump Electrical Circuit Diagnosis

Circuit Description

When the ignition switch is turned ON, the VCM turns the in-tank fuel pump ON. The in-tank fuel pump remains ON as long as the engine is cranking or running and the VCM is receiving the distributor reference pulses. If there are no reference pulses, the VCM shuts the fuel pump OFF within 2 seconds after the ignition was turned ON or if the engine stops. The VCM will also turn ON the fuel pump for 2 seconds when the ignition is turned to the OFF position.

Diagnostic Aids

If the fuel pump relay circuit checks out OK, refer to Fuel System Diagnosis.

Excessive fuel may also cause long cranking times which is accompanied by the following conditions:
^ A start that is not as fast as normal.
^ A puff of black smoke at the tailpipe.

A malfunctioning EVAP System Component can cause this problem. Refer to Evaporative Emission (EVAP) Control System Diagnosis.

One or more leaking poppet nozzles (CSFI injectors) may also extend the cranking time. Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

2. Command both the ON and OFF states. Repeat the commands as necessary.
3. This step determines if the condition is located on the coil side or the switch side of the circuit.
4. This step verifies that the VCM is providing voltage to the fuel pump relay.
5. This step tests for an open in the ground circuit to the fuel pump relay.
6. This step determines if a voltage is constantly being applied to the fuel pump relay.
12. To gain access to the fuel pump connector, the fuel tank may need to be removed, refer to Fuel Tank Replacement.
13. This step determines if the condition with the circuit is intermittent. If the fuse does not open, inspect the supply voltage circuit between the fuse and the fuel pump for an intermittent condition.
15. Use the same amperage fuse in the jumper as is used to protect the fuel pump circuit.
16. To gain access to the fuel pump connector, the fuel tank may need to be removed.
17. Inspect the splice pack which contains the fuel pump ground and other ground circuits. Be certain all connections within the splice pack are clean and tight.