S10/T10 Blazer 4WD V6-4.3L VIN W (1997)
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 Pressure Test. See: Computers and Control Systems/Testing and Inspection/Component Tests and General Diagnostics/Fuel
System Pressure Test
Excessive fuel may also cause long cranking times which is accompanied by the following conditions:
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A start that is not as fast as normal.
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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 Canister Hoses.
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. See: Computers and Control Systems/Testing and Inspection/Component Tests and General Diagnostics/Fuel Injector
Balance Test Procedure
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.
