C 1500 Truck 2WD V8-350 5.7L (1989)
Fuel Pump Relay: Description and Operation
Fuel Pump Relay
When the key is first turned ON, without the engine running, the ECM will turn the fuel pump relay ON for two seconds. This builds up the fuel pressure
to normal operating pressure. If the engine is not started within two seconds, the ECM will shut the fuel pump OFF and wait until ignition reference
pulses are present. On heavy duty models, a fuel module will override the ECM and the fuel pump will operate for approximately twenty seconds. This
corrects a hot restart (vapor lock) during a high ambient temperature condition. As soon as the engine is cranked, the ECM turns the relay ON, which
powers the fuel pump. The ECM continues to power the fuel pump during engine operation. If the fuel pump relay fails, it is backed up by the oil
pressure switch, which continues to operate the fuel pump as long as oil pressure remains above 28.0 kPa (4 psi).
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A faulty fuel pump relay can result in long cranking times, particularly if the engine is cold.
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An inoperative fuel pump would cause a no start condition. A fuel pump which does not provide enough pressure can result in poor performance.
