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| Illustration 1 | g03505585 |
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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) Fuel pressure sensor (7) Pressure relief valve (8) Electronic unit injector (9) Fuel cooler (optional) (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 up to a maximum pressure of
Fuel that has too high a pressure from the fuel manifold (rail) returns through the pressure relief valve to the return line. Fuel leak off from the electronic unit injectors flows to the return line. The fuel may then flow through an optional fuel cooler on the way back to the fuel tank.
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| Illustration 2 | g03505586 |
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Typical example (1) Fuel injection pump (2) Solenoid for the fuel injection pump (3) Pressure relief valve (4) Electronic unit injector (5) Fuel manifold (rail) (6) Fuel pressure sensor (7) Fuel transfer pump | |
The fuel injection pump (1) feeds fuel to the high-pressure fuel manifold (rail) (5). 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 priming the fuel system is required:
- A fuel filter is changed.
- A low-pressure fuel line is replaced.
- The fuel injection pump is replaced.
- The ECM is replaced, if a fuel cooled ECM is installed.
- Draining water from the water separator.
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 | g03346826 |
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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 is supplied loose. The primary filter/water separator is supplied with water in fuel sensor (2).
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| Illustration 4 | g03346829 |
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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.
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| Illustration 5 | g03346818 |
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Typical example | |
The fuel pump assembly consists of a low-pressure transfer pump (3) and a high-pressure fuel injection pump (1). The pump assembly is driven from a gear in the front timing case at half of the engine speed. The fuel injection pump (1) has two plungers that are driven by a camshaft. The fuel injection pump (1) delivers a volume of fuel three times for each revolution. The stroke of the plungers are fixed.
The injector will use only part of the fuel that is delivered by each stroke of the pistons in the pump. The solenoid (2) for the fuel injection pump (1) 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 (1) 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 | g03505592 |
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Typical example of the electrical control system for the fuel system (1) Electronic Control Module (ECM) (2) Throttle position sensor (3) Fuel pressure sensor (4) Engine oil pressure sensor (5) Inlet manifold pressure sensor (6) Air inlet temperature sensor (7) Inlet manifold air temperature sensor (8) Coolant temperature sensor (9) Secondary speed/timing sensor (10) Primary speed/timing sensor (11) Fuel injection pump (12) Solenoid for the fuel injection pump (13) Electronic unit injectors | |
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 proportional to 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 | g03347338 |
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Typical example (1) Electrical connections (2) Clamping bolt for the electronic unit injector (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.
When the ECM sends a signal to the injector solenoid, a valve inside the injector opens. The valve allows the high-pressure fuel from the fuel manifold to enter the injector. Fuel is also diverted via the leak-off route to cool and lubricate injector. The pressure of the fuel pushes the needle valve and a spring. The difference in pressure around the needle valve becomes too great, this causes the pressure to lift the needle and start injecting.
The timing and duration of injection is controlled by a solenoid valve in the injector. The valve has two positions. In the closed position, the valve closes the inlet to the injector. In this position, fuel above the injector needle is allowed to vent through the leakoff port.
In the open position, the valve opens the inlet to the injector. Simultaneously, the valve closes the leakoff port in order to allow high-pressure fuel to flow to the needle. When the solenoid valve is closed, some fuel escapes past the valve in order to vent through the leakoff port. A certain volume of fuel always flows from the leakoff port. If the volume of fuel increases beyond a critical level, the fuel injection pump will not be able to maintain pressure in the fuel manifold.
When the needle valve opens, fuel under high pressure will flow through nozzle orifices into the cylinder. The fuel is injected into the cylinder through the orifices in the nozzle as a very fine spray.
When the signal to the injector ends, the valve closes. The fuel in the injector changes to a low pressure. When the pressure drops the needle valve will close and the injection cycle stops.
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 provides the torque and power for the engine.
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| Illustration 8 | g03505596 |
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Typical example | |
The fuel manifold (3) stores high-pressure fuel from the fuel injection pump. The high-pressure fuel will flow to the injectors.
The fuel pressure sensor (2) measures the fuel pressure in the fuel manifold (3).
The pressure relief valve (1) will prevent the fuel pressure from getting too high.
The pressure relief valve and the fuel pressure sensor can be serviced as separate components.