Caprice V8-265 4.3L VIN W MFI (1995)
Fuel Pump Relay: Description and Operation
When the ignition switch is turned to the "ON" position (before engaging starter), the energizes the fuel pump relay for two seconds causing the fuel
pump to pressurize the fuel system. If the Powertrain Control Module (PCM) does not receive ignition reference pulses (engine cranking or running)
within two seconds, it shuts "OFF" the fuel pump relay, causing the fuel pump to stop.
As a backup system to the fuel pump relay the fuel pump also can be energized by the fuel pump switch and engine oil pressure sensor. The sensor has
two internal circuits. One operates the oil pressure indicator or gage on the instrument cluster, and the other is a normally open switch which closes when
oil pressure reaches about 28 kPa (4 psi). If the fuel pump relay fails, the fuel pump switch and engine oil pressure sensor runs the fuel pump.
An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold. The fuel pump switch and engine oil pressure sensor
energizes the fuel pump as soon as oil pressure reaches about 28 kPa (4 psi).
