S-Type (X200) V8-4.0L (AJ28) (2001)
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Fuel Pump Control Unit: Description and Operation
Fuel Pump Control and Operation
Fused B+ dedicated voltage to drive the fuel pump is supplied to the RECM from the rear power distribution box via the fuel pump relay. The relay is
activated by ignition switched B+ voltage via the inertia switch.
The PCM calculates engine fuel requirements using engine load, speed, air flow, temperatures, current fuel rail state from the IP and EFT sensors, and
other data inputs. The PCM communicates the fuel flow demand to the RFCM as a pulse width modulated (PWM) signal over a single line at a
frequency of approximately 256 Hz and a duty cycle of 0- 50%. The RECM effectively amplifies this signal by increasing the frequency by 64 and
doubling the duty cycle, thus providing the necessary high current drive for the fuel pump.
When the ignition switch is turned from OFF to RUN or START, the PCM primes the system by running the pump for 1 second. After prime, the pump
is switched ON when the CKP signal is received. The pump is switched OFF 1 second after the engine is stopped. During all hot fuel conditions, fuel
pressure is increased to prevent vapor lock.
Fuel pump drive status is monitored by the RECM and communicated to the PCM via the SCP network.
