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HOMESERVICE MANUALSCHEVROLET1987HI-CUBE 6.2 J, 400/M40REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 14 (ENGINE CONTROLS - THEORY & OPERATION - GASOLINE)FUEL SYSTEMFUEL DELIVERYFUEL PUMP RELAY
1987 Chevrolet Hi-Cube 6.2 J, 400/M40

Fuel Pump Relay

1987 Chevrolet Hi-Cube 6.2 J, 400/M40SECTION Fuel Pump Relay
WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 1994 GMC Yukon, 1994 GMC Suburban, 1994 GMC Pickup, 1994 GMC Cab & Chassis, and 1994 GMC C3500 HD. However, it is still accessible from the selected car via links, so may be relevant.

When ignition switch is turned to ON position, PCM turns electric fuel pump on by energizing fuel pump relay. PCM keeps relay energized if engine is running or cranking (PCM is receiving reference pulses from ignition module). If there are no reference pulses, PCM turns pump off within 2 seconds after key on. On "C" and "K" series with 5.7L over 8500 GVW, see FUEL MODULE under FUEL DELIVERY.

As a back-up system to fuel pump relay, the oil pressure switch also activates fuel pump. The oil pressure switch is normally open until oil pressure reaches about 4 psi (.28 kg/cm2 ). If fuel pump relay fails, the oil pressure switch closes when oil pressure is obtained, and operates the fuel pump. Cranking time will be longer if fuel pump does not receive current until oil pressure switch contacts close. Oil pressure switch may be combined into a single unit with an oil pressure gauge sending unit or sensor.

PCM monitors fuel pump circuit between fuel pump relay/oil pressure switch and fuel pump, enabling PCM to determine if fuel pump is being energized by fuel pump relay or oil pressure switch. A failure in this monitored circuit results in the setting of a related trouble code in PCM memory.

For additional information on fuel pump activation, see BASIC TESTING - GASOLINE article in the ENGINE PERFORMANCE section and SYSTEM/COMPONENT TESTS - GASOLINE article in the ENGINE PERFORMANCE section.

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