Circuit Diagnosis - Fuel Pump

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION
When the ignition switch is turned ON, the VCM turns ON the in-tank fuel pump. 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 off the fuel pump within 2 seconds after the ignition ON or the engine stops.
Should the fuel pump relay or the 12 volt relay drive from the VCM fail, the fuel pump receives a supply current through the oil pressure switch backup circuit. The fuel pump test terminal is located in the driver's side of the engine compartment. When the engine is stopped applying the battery voltage to the test terminal can turn on the fuel pump.

DIAGNOSTIC AIDS
An inoperative fuel pump relay can result in long cranking times. The time necessary for the oil pressure to reach the pressure required in order to close the oil pressure switch and supply the necessary current for the fuel pump causes the extended crank period. 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:
1. A start that is not as fast as normal. System Diagnosis - Fuel System
2. A puff of black smoke at the tailpipe An improperly connected or faulty EVAP canister control valve can cause this problem. Disconnect the EVAP purge hose from the EVAP canister control valve in order to diagnose. Refer to EVAP Control System Diagnosis. System Diagnosis - EVAP Control
One or more leaking poppet nozzles may also extend the cranking time. Perform the Poppet Nozzle Test, in the Injector Balance Test Table. Refer to Fuel Injector Balance Test. Fuel Injector Balance Test

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. This step checks for the correct operation of the fuel pump system. When the ignition is turned ON, the fuel pump should operate for about 2 seconds and then turn OFF. if no ignition reference pulses are detected by the VCM.
3. This step checks the operation of the fuel pump by applying a fused 12 volts directly to the fuel pump. At this point, the problem is isolated as a pump or a control circuit problem.
4. This step will determine if the VCM is able to control the fuel pump relay.
5. This step will detect a problem in the Fuel Pump Relay control circuit.
7. This step checks for battery voltage to the Fuel Pump Relay. No voltage could be the result of an open battery circuit or a blown VCM B fuse. If the VCM B fuse is blown, the scan tool may not communicate with the vehicle.
8. The oil pressure switch serves as a backup for the fuel pump relay in order to help prevent a No Start situation. If the fuel pump relay was found to be inoperative, test the oil pressure switch circuit in order to determine why the switch did not operate the fuel pump.