Circuit/System Description

The G18 High Pressure Fuel Pump is located at the right front of the engine and is engine driven by the timing belt. Fuel is pumped from the primary fuel tank and delivered through the diesel fuel conditioning module to the high pressure pump. The Engine Control Module (ECM) controls the fuel rail pressure using two pulse width modulated fuel rail pressure regulators. Q18A Fuel Pressure Regulator 1 is located on the fuel injection pump and meters the amount of fuel that enters the high pressure side of the pump. From the high pressure pump, the fuel moves to the fuel rail through a high pressure metal line. The fuel rail distributes high pressure fuel to all 4 fuel injectors. The ECM varies the pulse width modulated voltage to the Q18B Fuel Pressure Regulator 2 to relieve excessive fuel pressure which returns to the fuel tank. When the ignition is OFF, Q18B Fuel Pressure Regulator 2 opens to bleed off the pressure in the fuel rail.

At engine start, Q18B Fuel Pressure Regulator 2 controls fuel pressure at idle. The engine will remain in this mode if the fuel temperature is below 15°C (59°F) or until fuel pressure regulator 2 adapts (which occurs at higher engine loads) or until fuel temperature reaches 60°C (140°F). Once the adaptation is complete, the vehicle will use Q18A Fuel Pressure Regulator 1 to control rail pressure.