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Home >> GMC >> 1990 >> Forward Control 6.2 J, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Testing >> Chart A-5, Fuel Pump Relay Circuit Diagnosis >> C, K, R, V, G, P & GP Series >> Circuit Description

Circuit Description

When ignition switch is turned "ON," the ECM will turn "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the ECM is receiving distributor reference pulses. If there are no reference pulses, the ECM will shut "OFF" the fuel pump within two seconds after ignition "ON" or engine stops.

The pump will deliver fuel to the TBI unit where the system pressure is controlled to about 9-13 psi. Excess fuel is then returned to the fuel tank.

A fuel module is used on all 7.4L, G van with 5.7L, and all other 5.7L over 8500 GVW engines to correct a hot restart vapor (vapor lock) during a high ambient condition. It is designed to over-ride the ECM two second pump operation and will run the fuel pump for twenty seconds at initial ignition "ON".

NOTE: Numbers below refer to circled numbers on diagnostic chart.
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