Functional Description - High Pressure (Hp) Fuel Pump (Including FQS)
The high pressure fuel pump features:
- Fuel Quantity Solenoid
- Fuel supply to fuel rail
- Fuel intake
- Roller cup
This figure depicts the flow of fuel through the HP Fuel Pump
The 3.0L SO engine is equipped with one HP fuel pump and the 3.0L HO engine is equipped with two HP fuel pumps to meet demand.
The High Pressure (HP) fuel pump is directly operated by the camshaft. A roller cup is used between the six cam lobes on the fuel pump camshaft and the pump plunger stem to reduce friction. The HP fuel pump has a normally open inlet valve. There is a fine mesh filter on the inlet valve. The inlet valve is closed by the Fuel Quantity Solenoid (FQS). The Powertrain Control Module (PCM) controls the FQS with a Pulse Width Modulated (PWM) signal synchronized to the Camshaft position. The HP Fuel Pump operates as a spill valve, allowing the pump to spill fuel back through the inlet valve as the plunger moves down and up until the valve is closed. When the PCM determines that the remaining portion of the plunger upstroke would result in the correct fuel volume required to maintain rail pressure, the inlet valve is closed by the FQS and the remaining fuel in the chamber is pressurized past the outlet check valve and into the Fuel Rail.
If the PCM is unable to close the FQS, the low pressure fuel will pass through to the Fuel Rail and the pressure will equalize on the two sides.
The fuel system is under a constant high pressure (even with engine off). Before servicing any fuel system hose, fitting or line, fuel system pressure must be released.