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
If no trouble is found in the fuel pump circuit or the ignition system and the cause of an Engine Cranks But Will Not Run has not been found, check for the following conditions:

^ Fouled spark plugs.
^ An EGR valve stuck open.
^ Low fuel pressure. Refer to Fuel System Diagnosis. System Diagnosis - Fuel System
^ Water or foreign material in the fuel system.
^ A grounded Ignition Control (IC) signal circuit may cause a No Start or a Start then Stall condition.
^ Basic engine problem.

The VCM has integrated IC circuits that are fault protected; therefore, if a circuit has failed, the integrated IC may not be damaged. If that is the case, the IC will keep the circuit open until the fault in the circuit has been corrected.

When the fault has been corrected, reinstall the VCM and check the circuit. Replace the VCM only if the circuit is still inoperative.

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.