C 2500 Truck 2WD V8-350 5.7L (1988)
Fuel Pump Relay: Description and Operation
Wiring Diagram For Chart A-5 - Fuel Pump Relay Circuit Diagnosis (One Fuel Tank)
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.
