At key on, the fuel pump within the Diesel Fuel Conditioning Module (DFCM) is turned on and the low pressure fuel
system is pressurized. If the engine is not started, the pump runs for up to 30 seconds. The PCM obtains information from the Ambient Air Temperature (AAT), Engine Coolant Temperature (ETC) , Engine Oil Temperature (EOT) , and Fuel Rail Temperature (FRT) sensors for fuel delivery calculations. The Volume Control Valve (VCV) and Pressure Control Valve (PCV) are open.
During engine cranking the PCM identifies Top Dead Center (TDC) within approximately 120 degrees of crankshaft
rotation and PCV is closing, allowing fuel pressure in the rail to achieve the calibrated value. This allows the engine to
start very quickly.
Once the Fuel Rail Pressure (FRP) sensor detects the required fuel pressure, the PCM begins fuel injection operation to meet the desired idle RPM based upon the temperature sensors and engine load. During this initial start up mode, the high pressure fuel system is run in PCV mode for a calibrated amount of time. The VCV is set to a specified point while PCV is duty cycled to meet the desired fuel rail pressure.
The high pressure fuel system operates in PCV mode until a calibrated fuel temperature and time is achieved.
In VCV mode the fuel volume entering the high pressure fuel pump is adjusted by the VCV to meet the required fuel rail pressure while still being trimmed by the PCV. VCV mode is a more efficient operating mode because only the amount of fuel required for combustion is being compressed by the pump and sent to the fuel rails.
During acceleration, the VCV and PCV are commanded to meet the driverโs demand (accelerator pedal input/engine
load). The PCMโs commands to the VCV and PCV are based upon: FRT, ECT, EOT, ATT, engine load, and regeneration state.
On deceleration, the VCV is closed and the PCV is opening to max position to reduce fuel pressure. When RPM is
approaching the desired idle speed, the VCV begins to open to prepare for injector usage.
During regeneration, the left side injectors perform post injection. The right side injectors do not provide fuel for
regeneration because right side cylinders supply exhaust gas to the EGR valve and EGR cooler.
Under certain conditions, like battery disconnect and fuel system reset, the fuel system operates in Adaptive PCV (APCV) mode on the first start. In the APVC mode, the PCM is learning the duty cycle needed for the PCV to achieve the desired fuel pressure.
