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| Illustration 1 | g02511124 |
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Typical example (1) Primary fuel filter (2) Secondary fuel filter (3) Fuel Injection Pump (4) Fuel transfer pump (5) Fuel manifold (rail) (6) Pressure relief valve (7) Electronic unit injector (8) Manifold connector (9) Fuel cooler (if equipped) (A) Fuel tank | |
Fuel is drawn from the fuel tank to the 10 micron primary fuel filter and a water separator. The fuel then flows to the fuel transfer pump. The fuel transfer pump is part of the fuel injection pump.
Fuel then flows from the fuel transfer pump to the 4 micron secondary fuel filter. Fuel flows from the secondary fuel filter to the fuel injection pump.
At the fuel injection pump, the fuel is pumped at an increased pressure of up to
Fuel that has too high a pressure from the fuel manifold (rail) returns through the pressure relief valve to the return line. Fuel that is leak off from the electronic unit injectors flows to the return line. The fuel may then flow through a fuel cooler (if equipped) on the way back to the fuel tank.
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| Illustration 2 | g02493876 |
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Typical example (1) Fuel injection pump (2) Suction control valve for the fuel injection pump (3) Pressure relief valve (4) Fuel manifold (rail) (5) Electronic unit injector (6) Fuel pressure sensor (7) Fuel transfer pump | |
The fuel injection pump (1) supplies fuel to the high-pressure fuel manifold (rail) (4). The fuel is at a pressure of up to
Components of the Fuel Injection System
The fuel injection system has the following mechanical components:
- Primary filter/water separator
- Fuel transfer pump
- Secondary fuel filter
- Fuel injection pump
- Fuel injectors
- Fuel manifold
- Pressure relief valve
- Fuel pressure sensor
- Fuel temperature sensor
- Water in fuel sensor
The following list contains examples of both service and repairs when you must prime the system:
- A fuel filter is changed.
- A low-pressure fuel line is replaced.
- The fuel injection pump is replaced.
For the correct procedure to prime the fuel system, refer to Systems Operation, Testing and Adjusting, "Fuel System - Prime".
Primary Filter/Water Separator
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| Illustration 3 | g02848802 |
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Typical example | |
The primary filter/water separator (1) is located between the fuel tank and the fuel transfer pump. The primary filter/water separator (1) provides a 10 micron filtration level.
The primary filter/water separator can either be engine mounted or supplied loose. The primary filter/water separator is supplied with water in fuel sensor. The water in fuel sensor has to be connected.
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| Illustration 4 | g02848803 |
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Typical example | |
The secondary fuel filter (1) is located after the fuel transfer pump. The secondary fuel filter (1) provides a 4 micron filtration level.
The fuel temperature sensor measures the temperature of the fuel. The ECM receives the signal from the fuel temperature sensor. The ECM calculates the volume of fuel.
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| Illustration 5 | g02493877 |
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Typical example | |
The fuel pump assembly consists of a low-pressure transfer pump and a high-pressure fuel injection pump. The pump assembly is driven from a gear in the front timing case at one a half times the engine speed. The fuel injection pump (1) has one plunger that are driven by a camshaft. The stroke of the plunger is fixed but the volume of fuel that is provided by the fuel injection pump is controlled by the suction control valve.
The injector will use only part of the fuel that is delivered by each stroke of the pistons in the pump. The suction control valve (2) for the fuel injection pump is controlled by the ECM. This maintains the fuel pressure in the fuel manifold (rail) at the correct level. A feature of the fuel injection pump allows fuel to return to the tank continuously.
The fuel injection pump has the following operation:
- Generation of high-pressure fuel
The fuel output of the fuel injection pump is controlled by the ECM in response to changes in the demand of fuel pressure.
The engine shuts off by preventing the electronic unit injectors from injecting. The ECM then closes the suction control valve to prevent the pressure in the fuel manifold (rail) from increasing.
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| Illustration 6 | g02511078 |
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Typical example of the electrical control system for the fuel system (1) Electronic Control Module (ECM) (2) Electronic unit injectors (3) Suction control valve (4) Fuel injection pump (5) Crankshaft position sensor (6) Camshaft position sensor (7) Coolant temperature sensor (8) Fuel temperature sensor (9) Inlet manifold air temperature and pressure sensor (10) Oil pressure switch (11) Fuel pressure sensor (12) Pressure sensor for the NOx Reduction System (NRS) (13) Wastegate regulator (14) Water in fuel sensor (15) Throttle position sensor | |
The ECM determines the quantity, timing, and pressure of the fuel in order to be injected into the fuel injector.
The ECM uses input from the sensors on the engine. These sensors include the speed/timing sensors and the pressure sensors.
The ECM controls the timing and the flow of fuel by actuating the injector solenoid.
The amount of fuel is injected is a function of fuel pressure in the fuel manifold and the duration of the signal to the injector solenoid.
The ECM controls the fuel pressure by increasing or decreasing the flow of fuel from the fuel injection pump.
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| Illustration 7 | g02493878 |
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Typical example (1) Electrical connections (2) Bolt (3) Clamp (4) Combustion washer (5) O-ring (6) Fuel inlet | |
The fuel injectors contain no serviceable parts apart from the O-ring seal and the combustion washer. The clamp and setscrew are serviced separately.
The injector nozzle and control piston volume are continuously connected to the fuel manifold (rail) through the high-pressure fuel line. The nozzle needle is controlled by the control piston, which in turn is controlled by the pressure in the control piston volume. The injector contains a solenoid valve that controls the spill flow from the control piston volume. The control piston volume has an inlet throttle and an outlet throttle. The sizing of the throttles determines the rate of pressure decay in the control volume and hence the rate of nozzle opening. By opening the solenoid valve, fuel flows out of the control volume lowering its internal pressure which allows nozzle pressure to lift the needle and control piston, this enables injection to occur.
To end injection, the solenoid valve is closed. Closing the solenoid valve blocks off the control volume outlet orifice which causes the control volume pressure to increase. By increasing control volume pressure, this forces the control piston, and needle, back down until the needle reseats in the nozzle. The injection process ends.
The needle valve has a close fit with the inside of the nozzle. This makes a positive seal for the valve.
The electronic unit injectors can be instructed to inject fuel multiple times during the combustion process. A close pilot injection occurs before the main injection. The close pilot injection helps to reduce NOx and noise. The main injection period helps to increase the torque of the engine. The after injection period helps to reduce the amount of smoke that is produced.
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| Illustration 8 | g02493879 |
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Typical example | |
The fuel manifold (2) stores high-pressure fuel from the fuel injection pump. The high-pressure fuel will flow to the injectors.
The fuel pressure sensor (3) measures the fuel pressure in the fuel manifold (2).
The pressure relief valve (1) will prevent the fuel pressure from getting too high.