K 1500 Truck 4WD V8-305 5.0L VIN M SFI (1996)
Fuel Pump Relay: Description and Operation
Fuel Pump Relay Operation
OPERATION
When the key is turned ON with out the engine running, the control module turns a fuel pump relay ON for two seconds. This builds up fuel pressure
quickly. If the engine is not started within two seconds, the control module shuts the fuel pump OFF and waits until the engine starts. As soon as the
engine is cranked, the control module turns the relay ON and runs the fuel pump. When the engine is cranking or running, the control module receives
the Crankshaft Position (CKP) sensor reference pulses which in turn energize the fuel injectors. As a backup system to the fuel pump relay, the fuel
pump can also be turned ON by a fuel pump oil pressure switch. When the engine reaches about 28 kPa (4 psi), and the fuel pump relay does not
complete the circuit, the fuel pump oil pressure switch will close to complete the circuit to run the fuel pump.
An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold. The fuel pump oil pressure switch will turn ON the
fuel pump as soon as oil pressure reaches about 28 kPa (4 psi).
