Theory Of Operation
General Operation: The Direct Injection system sprays fuel at a very high pressure directly into the combustion chamber. There are two sides to the fuel system, the low pressure (supply) side and high pressure (control) side. The high pressure is created by the High Pressure Fuel Pump assembly (described below). The Powertrain Control Module (PCM) monitors the fuel pressure on both sides of the system.
- Low Pressure (supply) Side: The low pressure side of the system uses an electric Fuel Pump Module in the Fuel Tank to supply fuel to the High Pressure Fuel Pump at approximately 520 kPa (75.4 psi). The PCM receives feedback from the Fuel Pressure Sensor to monitor the low pressure supply side of the system.
- High Pressure (control) Side: The fuel pressure is increased by the High Pressure Fuel Pump which has a plunger that is mechanically driven by four lobes on the Camshaft. The fuel pressure on the high side of the system is regulated by a Fuel Quantity Solenoid (FQS). The FQS is integrated on the High Pressure Fuel Pump. The high fuel pressure to the Common Fuel Rail and Fuel Injectors can vary based on engine needs. The PCM receives feedback from the Fuel Rail Pressure (FRP) Sensor to monitor and regulate the pressure on high pressure side.
The 3.0L High Output (HO) engine uses two high pressure fuel pumps to meet the demand on the fuel system under certain loads. To meet the added supply necessary for the two high pressure fuel pumps there are two low pressure fuel pumps in the fuel tank. The low pressure pumps supply fuel through a common supply line to the two high pressure fuel pumps. Both high pressure fuel pumps and fuel quantity solenoids operate in the same manner as described below in the High Pressure Fuel Pump Operation.
High Pressure Fuel Pump Operation: To control the pressure, the PCM uses a rail mounted Fuel Rail Pressure (FRP) Sensor and a normally open inlet valve integral to the engine mounted High Pressure Fuel Pump. The inlet valve is closed by the Fuel Quantity Solenoid. The PCM controls the Fuel Quantity Solenoid with a Pulse Width Modulated (PWM) signal synchronized to the Fuel Pump Camshaft position. The High Pressure 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 two sides will equalize.
The figure below depicts the flow of fuel through the High Pressure Fuel Pump.
Diagnostics: The PCM performs diagnostics on the Fuel Quantity Solenoid, Fuel Pressure Sensor, Fuel Rail Pressure (FRP) Sensor and wiring for opens or shorts. An open or short in any of the sensors or related wiring will result in a correlating circuit fault. The FRP Sensor has a shared 5-Volt Supply and Sensor Ground. There are two internal pressure sensors that provide signals to the PCM for redundancy. The PCM performs circuit diagnostics on each signal as well as a rationality diagnostic. The PCM compares the desired fuel rail pressure to the actual fuel rail pressure. If the difference between the two is more than a calibrated threshold, a fuel system performance fault is set.
The fuel system is under a constant pressure high pressure (even with engine off). Before servicing any fuel system hose, fitting or line, fuel system pressure must be released. Refer to FUEL SYSTEM PRESSURE RELEASE .