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| Illustration 1 | g06018407 |
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(1) ECU
(2) Electric priming pump with filter, water separator, and water-in-fuel switch (3) Fuel tank (4) Fuel cooler (5) Cylinder head total backflow draining LP line (6) Relief to tank line (7) Relief valve (8) Backflow LP channels in cylinder head block (9) Rail to injectors HP line (10) Rail pressure sensor (11) Hydraulic accumulator (12) HP line from fuel pump to rail (13) HP fuel pump (14) Fuel pump outlet LP line (15) HP Pump backflow draining LP line (16) Fuel pump inlet LP line (17) Low-pressure fuel system pressure sensor (18) Fuel filter — with: Fuel delta-pressure switch / Fuel temp sensor (19) LP line pump inlet | |
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| Illustration 2 | g06018384 |
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(20) Fuel pump
(21) Main fuel filter (22) Common rail (23) Injector (24) ECM Cooler (25) Fuel inlet to engine (26) Electric priming pump with filter, water separator, and water-in-fuel switch (27) Fuel Cooler (28) Fuel outlet from engine | |
This fuel system consists of five major components:
- High-pressure fuel pump (13)
- Engine Control Module (ECM) (1)
- Fuel Injectors (23)
- Fuel rail (22)
- Fuel transfer pump (20)
- Priming pump (26)
The transfer pump (20) pulls fuel from the fuel tank (1) through the fuel filter/ water separator priming pump (25). Transfer pump (20) sends the fuel through the ECM to cool the ECM. Fuel pressure sensor (17) measures the fuel pressure at the inlet of the fuel filter. The fuel flows through the main fuel filter (2) to the high-pressure fuel pump (13). The high-pressure fuel pump (13) pressurizes the fuel that is sent to the fuel rail (22). The fuel rail (22) distributes the fuel to the fuel injectors (23) by the use of fuel lines. The fuel rail uses a rail pressure sensor (10) that tells the ECM (1) the pressure of the fuel rail. The ECM receives engine speed from the speed/timing sensor. The ECM controls the pressure regulator for the high-pressure fuel pump (14) to obtain the correct amount of pressure. If pressure at the fuel rail is too high, the pressure relief valve (13) opens. This valve opening drains the excess fuel back to the fuel tank. The rail pressure can vary from 25 MPa to 180 MPa. Once the fuel reaches the injectors, ECM sends current to the injector solenoid to actuate the three-way valve inside the injector. As the valve opens, the fuel flows from the high-pressure line to the tip. As the valve opening pressure is reached, the check is lifted and fuel is delivered at high pressure into the combustion chamber. The fuel is then delivered in a precise quantity and at the right time. The injector returns the excess fuel to the tank through a check valve and a pressure regulator.
Engine Control Module (ECM) is on the left side of the engine. The ECM is a powerful computer that provides total electronic control of engine performance. The ECM uses data from engine performance that is gathered by several sensors. Then, the ECM uses this data to adjust the fuel delivery, injection pressure, and injection timing. The ECM contains programmed performance maps (software) to define horsepower, torque curves, and rpm. This software is commonly called the personality module.
ECM logs faults of engine performance. Also, the ECM can run several diagnostic tests automatically when the ECM is used with an electronic service tool such as the Cat ET.
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| Illustration 3 | g06018481 |
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(29) Priming pump/fuel filter inlet
(30) Priming pump/fuel filter outlet (31) Electric priming pump (32) Primary fuel filter (33) Water separator | |
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| Illustration 4 | g06018490 |
| (34) Air purge valve | |
The electric priming pump forces the air that is in the fuel system out of the system through manually operated valve on the fuel filter base. Priming via the manually operated air purge valve (32) on the fuel filter base is required only after servicing the fuel system or a fuel system filter change. When the fuel system has air trapped in the fuel filters, lines, and other fuel system components, the engine could experience difficulty starting. The ECM electronically controls the fuel priming pump relay. The fuel priming pump runs for 150 seconds after the keyswitch is turned to the ON or remote start position unless the engine reaches low idle rpm. Once one of these conditions are met, the engine speed has to come back to zero to start the priming cycle again.
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| Illustration 5 | g06049413 |
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(34) Fuel to rail
(35) Fuel intake from filter (36) Fuel intake from tank (37) Fuel outlet to filter (38) Cap (39) Fuel pump (40) Fuel outlet to tank | |
Fuel transfer pump is a pump that produces low pressure, high volume to pull fuel from the tank and through the primary fuel filter. Then, the pump sends the fuel through the secondary filter on the way to the high-pressure fuel pump. The high-pressure fuel pump feeds the injectors.
Fuel transfer pump is mounted on the back of high-pressure fuel pump. The fuel transfer pump is driven by the shaft of the high-pressure fuel pump.
High-pressure fuel pump (40) pressurizes the fuel to 25 MPa to 180 MPa. The high-pressure fuel pump is on the right rear corner of the engine.
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| Illustration 6 | g03658148 |
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Rail pressure sensor | |
The rail pressure sensor is installed in the front of the high-pressure fuel rail. The rail pressure sensor monitors the fuel pressure that is inside the fuel rail. The rail pressure sensor sends an analog voltage signal back to ECM. The ECM interprets the signal. The ECM is aware of the fuel pressure always.
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| Illustration 7 | g06018552 |
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(41) Solenoid
(42) Fuel supply (43) O-ring (44) Cooling orifice (45) Sealing washer (46) Nozzle | |
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| Illustration 8 | g06018559 |
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Section view of the injector (41) Solenoid (42) Fuel supply (46) Nozzle | |
The common rail fuel system utilizes electronic controlled fuel injectors. This system uses electronically actuated solenoid (41) to control the injection of the fuel into the combustion chamber.
The pressurized fuel enters fuel supply (42). Then, the solenoid lifts the needle against the valve inside the nozzle to allow the high-pressure fuel to be injected into the combustion chamber. There are orifices present in injector nozzle (46) that the fuel is injected through. The fuel is injected in precise amounts to control engine performance.
There are many other operating conditions when the injection pressure is between the minimum and the maximum. Regardless of the speed of the engine, the fuel system provides complete control of injection pressure.