K 3500 Truck 4WD V8-454 7.4L (1994)
Fuel Pump Relay: Testing and Inspection
*** UPDATED BY TSB 893206E, DATED OCTOBER 90
When the key is first turned ON, without the engine running, the control module 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 control module will shut the fuel pump OFF and
wait until ignition reference pulses are present. As soon as the engine is cranked, the control module turns the relay ON, which powers the fuel
pump. The control module 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).
RESULTS OF INCORRECT FUEL PUMP SYSTEM OPERATION
-
A faulty fuel pump relay can result in long cranking times, particularly if the engine is cold.
-
An inoperative fuel pump would cause a no start condition.
-
A fuel pump which does not provide enough pressure can result in poor performance.
