Applications Using a Fuel Pump Relay for Fuel Pump On/Off Control
The Fuel Pump (FP) is a PCM output signal that is used to control the electric fuel pump. With the electronic Engine Control (EC) power relay contacts closed, Vehicle Power (VPWR) is sent to the coil of the fuel pump relay. For electric fuel pump operation, the PCM grounds the FP circuit, which is connected to the coil of the fuel pump relay. This energizes the coil and closes the contacts of the relay, sending B+ through the Fuel Pump Power (FP PWR) circuit to the electric fuel pump. When the ignition key is turned on, the electric fuel pump runs for about one second, but is then turned off by the PCM if engine rotation is not detected.
For applications with two speed fuel pumps, a normally closed low speed fuel pump relay (Figure 49) is wired into the fuel pump ground circuit With the low speed fuel pump relay contacts in the normally closed position, there is no extra resistance in the ground circuit for high speed operation. For low speed fuel pump operation, the PCM will ground the Low Fuel Pump (LFP) circuit, which opens the relay contacts. With the relay contacts open, the fuel pump ground circuit now passes through a resistor that is wired into the circuit.
Fuel Pump Driver Module Applications (and Applications with Fuel Pump Functions Incorporated in Rear Electronic Module)
NOTE: For the LS6/LS8, the Fuel Pump Driver Module (FPDM) functions are incorporated in the Rear Electronic Module (REM) . Fuel pump operation is the same as applications using the stand-alone FPDM. The REM will, however, communicate diagnostic information through the BUS +/- circuits (SCP) instead of using a Fuel Pump Monitor (FPM) circuit.
Fuel Pump Duty Cycle Output From PCM
The Fuel Pump (FP) signal is a duty cycle command sent from the Powertrain Control Module (PCM) to the Fuel Pump Driver Module (FPDM) (Table 2). The FPDM uses the FP command to operate the fuel pump at the speed requested by the PCM or to turn the pump off.
