Theory Of Operation

This system utilizes a dual Fuel Pump and two Fuel Pump Control Modules (FPCM) to deliver fuel to the engine. The primary Fuel Pump and FPCM supply fuel under all normal conditions as requested by the PCM. The secondary Fuel Pump and FPCM (2) supply additional fuel to the engine at the request of the PCM during high fuel demand conditions as a supplement in order to maintain the appropriate volume and pressure to the Fuel Injectors. This fuel system utilizes additional DTCs to differentiate between fault conditions between the two fuel delivery systems. The operation and diagnostics of the secondary system are the same as the primary system.

When the Powertrain Control Module (PCM) receives a 'Start' or 'Run' signal, it energizes the Fuel Pump Relay which sends a continuous 12 volt supply to the Fuel Pump Control Module (FPCM). The PCM also sends a Pulse Width Modulated (PWM) control signal directly to the FPCM which regulates the PWM voltage that will be sent to the Fuel Pump. The PWM will vary from 10-100% depending on the input of the Fuel Rail Pressure Sensor and other engine demands. The PCM receives a PWM signal from the FPCM representing the state of all inputs and outputs of the FPCM. This system is a variable pressure fuel system. The pressure can change during different modes of engine load and operation. Ambient temperature and fuel temperature can also contribute to fuel pressure changes. The pressure is raised during high ambient temperatures to prevent boiling of the fuel. If a pressure sensor fails or other failures are present; The duty cycle goes to a default setting (80%) to maintain fuel pressure.