Fuel Charging and Controls
Fuel Charging and Controls
System Overview
WARNING: Avoid contact with fuel during a visual inspection for fuel leaks with the engine running. Do not work on the fuel system until the pressure has been released and the engine has cooled. Fuel in the high-pressure fuel system is hot and under very high pressure. High-pressure fuel may cause cuts and contact with hot fuel may cause burns. Failure to follow these instructions may result in serious personal injury.
WARNING: Contact with exposed fuel injector wiring, if energized, may result in electric shock. Use care when working on or around energized fuel injector wiring. Fuel injector wiring supplies high voltage to operate the fuel injectors. Failure to follow this instruction may result in serious personal injury.
NOTICE: Before disconnecting any part of the fuel system, it is important that all dust, dirt and foreign material is removed from around components to prevent ingress of foreign matter into the fuel system or the vehicle may be damaged.
NOTICE: The fuel tubes between the pump and the fuel rail, and the fuel rail and the injectors, must be discarded after each use and new tubes installed or the vehicle may be damaged.
NOTICE: It is essential that absolute cleanliness is observed when working with these components. Always install Fuel System Caps to any open orifice or tubes, or the vehicle may be damaged.
NOTICE: Make sure that the workshop area in which the vehicle being worked on is as clean and dust-free as possible. Areas in which work on clutches, brakes or where welding or machining are carried out are not suitable due to the risk of contamination to the fuel system. Failure to follow this instruction may result in damage to the vehicle.
NOTICE: Use a steel-topped work bench or cover it with clean, lint-free, non-flocking material. Failure to follow this instruction may result in damage to the vehicle.
NOTICE: Do not attempt to apply battery voltage to the fuel injector or damage to the fuel injector will occur.
NOTICE: The PCM is programmed with an IQA code for each fuel injector. The cylinder location of each fuel injector must be recorded.
The high-pressure common rail fuel system used on the 6.7L direct injection turbocharged diesel engine is controlled electronically by the PCM. Piezo-actuated fuel injectors deliver the high-pressure fuel. The injection parameters are:
- Injection pressure
- Number of injections per combustion cycle
- Timing of injections
- Injection quantity
These parameters are utilized for each injection phase within the combustion cycle. This system uses pre-injection (pilot), main-injection and post-injection to meet the following engine operating criteria:
- Engine system emissions
- Combustion noise reduction
- Engine performance
Component List
The high-pressure fuel system components consist of the following:
- high-pressure fuel injection pump mounted at the front of the engine block valley.
- high-pressure fuel rails mounted to each valve cover.
- piezo-actuated fuel injectors installed in the cylinder heads.
- fuel pressure control valve mounted to the rear of the LH fuel rail.
- fuel volume control valve mounted to the top of the high-pressure fuel injection pump.
- Fuel Rail Pressure (FRP) sensor mounted to the front of the LH fuel rail.
- secondary fuel filter mounted to the LH valve cover (low pressure).
- fuel injection pump supply tube routed from the secondary fuel filter to the high-pressure fuel injection pump (low pressure).
- fuel rail supply tubes routed from the high-pressure fuel injection pump to the fuel rails.
- fuel injector supply tubes routed from the high-pressure fuel rails to individual injectors.
- fuel injector return hose attached to each fuel injector and the secondary fuel filter.
System Diagram
High-Pressure Fuel System Flow
System Components
The secondary fuel filter receives fuel from the diesel fuel conditioning module and the fuel injector return hose.
The high-pressure fuel injection pump is mounted at the front of the engine valley and is driven by the camshaft gear. The high-pressure fuel injection pump gear is attached to the pump using a RH-threaded fastener.
High-Pressure Fuel Injection Pump
The high-pressure fuel injection pump supply tube supplies fuel from the secondary fuel filter to the high-pressure fuel injection pump.
The fuel pressure control valve bleeds off excess fuel rail pressure.
The fuel volume control valve controls the volume of fuel entering the 2 cylinders of the injection pump.
The high-pressure fuel rails distribute fuel to each of the injectors via individual steel injector supply tubes.
The PCM uses the fuel rail pressure sensor to determine the actual fuel rail pressure.
The PCM controls the duty cycle of the volume control valve and the fuel pressure control valve to maintain fuel rail pressure.
The fuel injector sprays high-pressure fuel into the combustion chamber.
Piezo Actuated Fuel Injector Externals
Piezo Actuated Fuel Injector Internals
Fuel Injector Replacement Label
Fuel Injector IQA Label
The fuel rail supply tubes distribute high-pressure fuel from the high-pressure fuel injection pump to the LH fuel rail and from the LH fuel rail to the RH fuel rail.
The fuel injector return hose collects fuel injector return fuel from the fuel injectors and delivers it to the inlet of the secondary fuel filter.
System Operation
Fuel supplied to the combustion chamber passes through the chassis-mounted diesel fuel conditioning module and chassis fuel tubes into the engine-mounted secondary fuel filter module. The low-pressure filtered fuel enters the high pressure fuel pump via a tube assembly containing a fuel temperature sensor and a fuel pressure switch. The fuel temperature sensor provides input to the PCM to control fuel system operating parameters, and the fuel pressure switch makes sure the minimum fuel supply pressure required by the high pressure fuel injection pump is being achieved.
Once the fuel enters the high pressure fuel injection pump, it flows through the cam chamber where it cools and lubricates the pumping components. A mechanical pressure regulator in the pump maintains a constant internal pressure. A fuel volume control valve is mounted on top of the high pressure fuel injection pump and allows a PCM-controlled portion of the low pressure fuel to flow to the two cylinders of the pump, where it is compressed and sent to the fuel rails. The high-pressure fuel injection pump generates pressures up to 200 MPa (2,000 bar or 29,007 psi).
The longer LH fuel rail contains a volume that is separated from the rest of the rail. Fuel is received into the volume end of the rail from the high pressure fuel injection pump via two fuel rail supply tubes, and released to the rest of the LH fuel rail through an orifice and to the RH rail through a fuel rail supply tube. The Fuel Rail Pressure (FRP) sensor measures the fuel pressure in LH fuel rail while the fuel pressure control valve controls the fuel pressure. The fuel pressure control valve is mounted on the rear of the LH fuel rail.
The PCM uses various inputs to determine high pressure fuel system operating mode. Under certain conditions, including startup, the system operates with the fuel volume control valve fully open, and fuel pressure is controlled by the fuel pressure control valve. In other operating conditions, the fuel volume control valve meters fuel so that only the amount of fuel required for a given rail pressure is compressed and sent to the rails. In this operating mode the fuel pressure control valve serves a trim function, bleeding off only small amounts of fuel.
The fuel injectors are controlled by the PCM using an internal injector driver. The fuel injectors use a piezo actuator, rather than a solenoid, to control fuel injection. The piezo actuator provides accurate control of injection timing and fuel quantity per injection event; there can be up to 5 injection events per combustion cycle. The fuel injector nozzle contains 8 fuel delivery orifices that provide an extremely fine fuel spray into the combustion chamber. The PCM-controlled fuel injector injects fuel into the combustion chamber at pressures up to 200 MPa (2,000 bar or 29,000 psi). Each fuel injector is assigned a fuel flow trim code during the injector manufacturing process. The fuel trim code is referred to as Injector Quantity Adjustment (IQA ). The PCM is programmed with the IQA code of the fuel injector for each cylinder. If a fuel injector is replaced, install the label that came with the new injector to the oil separator housing, and program the PCM with the new IQA code for that replacement injector.
The return fuel from the high pressure fuel injection pump combines with the return fuel from the fuel rail and is routed to the fuel cooler, mounted on the left frame rail, and then to the diesel fuel conditioning module. The return fuel from the fuel injectors flows through the injector return hose to a tee containing an orifice controlling the backpressure on the injectors, and from the tee back into the secondary fuel filter inlet fitting. During engine cranking, fuel pressure from the diesel fuel conditioning module is applied to the injector return connectors through this return hose to create the backpressure necessary for the injectors to function. During normal operation, injector return fuel flowing though the orifice creates the required backpressure.