Theory Of Operation

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The Fuel Quantity Solenoid (FQS) works in tandem with the Fuel Pressure Regulator (FPR) to control fuel volume and pressure in the Fuel Rail. The FQS is positioned in the inlet side of the High Pressure Delivery Pump (HPDP). The FQS receives 12 Volts and a duty-cycle ground signal from the Powertrain Control Module (PCM). The FQS is normally open, so when the FQS is not actuated (no ground signal from the PCM), the HPDP inlet passage is open allowing full fuel flow to the pumping chambers inside the HPDP. When the PCM grounds the FQS control signal the FQS closes the fuel inlet passage, preventing fuel from entering the pumping chambers. The FPR is positioned at the return passage of the Fuel Rail. The FPR is normally open and when the solenoid is not actuated (no ground signal from the PCM), the Fuel Rail return passage opens allowing fuel pressure in the rail to escape into the return circuit and on to the Fuel Tank. When the PCM grounds the FPR control signal, the solenoid valve closes allowing fuel pressure to build in the rail. The Fuel Pressure Regulator is not serviceable separate of the Fuel Rail Assembly.