Circuit Diagnosis - Fuel Pump

Diagnostic Chart:

Diagnostic Chart (cont'd):

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. System Diagnosis - Fuel System

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 An improperly connected or faulty Evaporative Emissions (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.

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.
3. This step checks the operation of the fuel pump by supplying 12 volts to the fuel pump control circuit.
5. This step checks the battery feed circuit to the fuel pump relay.
10. This step checks for the proper operation of the fuel pump relay.