General Operation of the Fuel System
Refer to Systems Operation, Testing, and Adjusting, "General Information" for locations of the components for the fuel system.
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| Illustration 1 | g03059777 |
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Typical example (1) Fuel tank (2) Primary fuel filter/water separator (3) Fuel transfer pump (4) Secondary fuel filter (5) Fuel injection pump (6) Fuel injectors (7) Fuel return line from the fuel injection pump and the fuel injectors to the fuel tank | |
When the engine is cranking, the fuel is pulled from the fuel tank (1) by the electric fuel transfer pump (3). A primary fuel filter/water separator (2) is installed between the fuel tank (1) and the fuel transfer pump (3). The primary fuel filter/water separator has an inline style filter. Refer to Operation and Maintenance Manual for more information on the service of the primary fuel filter/water separator. The fuel transfer pump forces the fuel through the secondary fuel filter (4) to the fuel injection pump (5).
The secondary fuel filter (4) can also function as a water separator. The secondary fuel filter can be drained through a valve that is located at the bottom of the filter housing.
The fuel injection pump sends fuel at high pressure to each fuel injector nozzle (6). The fuel injector nozzle sprays fuel into a precombustion chamber which slows the rate of combustion in the cylinder. The following items will result from reducing the rate of fuel combustion: prevention of engine knock, reduction of noise and reduction of emissions.
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| Illustration 2 | g00468241 |
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Phases of operation of the fuel injection nozzle (A) Closed valve (B) Open valve (C) Fully open valve | |
The fuel injection nozzle injects fuel into the precombustion chamber at different angles during two phases. Most of the fuel is injected when the valve is fully open (C). This process is called indirect fuel injection. The results are more even combustion and complete combustion of the fuel at a reduced temperature. Improved fuel combustion will increase power output while reducing emissions and reducing fuel consumption.
Excess fuel from the fuel injection nozzles and the fuel injection pump flows through fuel return line (7), through the injectors in the ARD and back to the fuel tank (1). The excess fuel aids the cooling of the fuel injection nozzles. Also, the fuel return line removes any air that is trapped in the fuel injection nozzles and the fuel injection pump.
The fuel injection pump needs fuel for lubrication. If the precision parts of the pump are not adequately lubricated, the components may be easily damaged. The engine must not be started until the fuel injection pump is full of fuel that is free of air.
The system must be primed by the electric fuel priming pump when any part of the system is drained of fuel. The following list contains examples of both service and repairs when you must prime the system:
- The fuel filter is changed.
- The low-pressure fuel line is removed.
- The fuel injection pump is removed.
- The fuel injection nozzles are removed.
- The fuel tank is drained.
- A leak exists in the low-pressure side of the fuel system.
In order to release air from the fuel injection pump and the fuel injection nozzles, refer to Systems Operation, Testing, and Adjusting, "Fuel System - Prime".
The fuel rack is connected to the linkage, which controls the fuel injection pump. This linkage is located in the front housing.
These engines have a mechanical governor in order to control engine speed. The governor operates for all engine rpm. The governor weight assembly is installed on the front of the gear of the camshaft. The other components of the governor are installed in the front housing.
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| Illustration 3 | g03335322 |
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Typical example of the governor control mechanism in the front housing (1) Connection for the linkage to the fuel injection pump (2) Control lever (3) Lever return spring (4) Governor adjustment screw (5) Arm | |
The movement of the governor weight assembly is transferred to the fuel rack on the fuel injection pump by the control lever (2), the governor lever (5), and the linkage to the fuel injection pump. The governor main spring (3) connects the governor lever to the control lever. The governor main spring controls the movement of the governor weight assembly on the camshaft. When the angle of the control lever changes, the tension on the governor main spring changes. This action controls the linkage to the fuel rack on the fuel injection pump, which controls the engine rpm.
The maximum fuel adjustment screw is mounted in the front housing. The maximum fuel adjustment screw is set to the full fuel position. This limits the maximum fuel that can be injected into the engine in case the fuel rack solenoid and position sensor is in fully open position. The fuel rack solenoid and position sensor controls the fuel delivery by limiting the mechanical fuel allowance.
Adjustments to the pump timing, should only be made by personnel that have had the correct training. The timing for the fuel injection pump should only change if the camshaft or the cylinder block are replaced. The fuel injection pump timing should not change if the fuel injection pump is reinstalled with a shim that is the same size.
The fuel rack automatically returns to the excess fuel position when the engine is stopped with the stop solenoid is energized and the engine is not running. The excess fuel position aids the cold starting of the engine.
A spring connects the linkage to the fuel injection pump and mechanical stop control (2). When the engine is first started, the spring automatically increases the fuel flow to the cylinders.
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| Illustration 4 | g00746909 |
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Fuel injection pump (typical example) (1) Fuel line to the fuel injection nozzles (2) Fuel delivery valve (3) Nuts and bolts for mounting the fuel injection pump to the cylinder block (4) Shim (5) Vent screw for the fuel injection pump (6) Fuel flow from the fuel transfer pump | |
The engines have the energized-to-run system for starting the engine and stopping the engine. The fuel rack solenoid and position sensor must be energized in order for fuel to flow to the engine cylinders.
The fuel injection pump is a cassette type pump. The cassette type pump contains the following components: fuel delivery valves, fuel rack and pushrods. The fuel injection pump is installed directly into the cylinder block.
The part number and code letters for the fuel injection pump are stamped on the front of the pump.
The fuel injection pump is a pressurized system that is totally enclosed. The pump sends the correct amount of fuel under high pressure at the correct time through the fuel injection nozzles to the individual cylinders. The fuel injection occurs near the end of the compression stroke. The fuel injection pump regulates the amount of fuel that is delivered to the fuel injection nozzles. This action controls the engine rpm by the governor setting or the position of the throttle control.
The camshaft is driven by the idler gear in the front gear case. Lobes on the camshaft cause the pushrod for each cylinder to reciprocate. The reciprocating motion first draws the fuel. The reciprocating motion then pressurizes the fuel. A fuel delivery valve (2) for each cylinder acts as a check valve in order to prevent a loss of pressure to the fuel injection nozzle.
The correct operation of the fuel injection pump requires the pump to be completely full of fuel and empty of air. When vent screw (5) is loosened, air can escape from the fuel injection pump.
The fuel injection pump will lubricate the components during operation.
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| Illustration 5 | g00836660 |
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(1) Fuel injection nozzle
(2) Washer | |
The washer (2) helps to prevent blowby. The washer also sets the projection of the fuel injection nozzle (1) into the precombustion chamber. This projection affects the time that is required for combustion in the cylinder. If the projection is excessive, engine knock can occur at high rpm.
Note: When a fuel injection nozzle (1) is installed in the cylinder head, a new washer (2) should be installed.
The operating pressure of the fuel injection nozzle is set and tested at the factory. Refer to Specifications, "Fuel Injection Nozzles" for the pressure settings of the fuel injection nozzle.
During operation, extra fuel is used as coolant and lubricant for components of the fuel injection nozzle.
Power to the electric fuel transfer pump is supplied through a relay when the keyswitch is turned to the START position. The motor that is located inside the electric fuel transfer pump will start to spin. The electric fuel transfer pump then creates a vacuum in order to force fuel from the fuel tank. Pressure is created in order to pump the fuel to the fuel injection pump.
The outlet valve and the inlet valve operate as check valves. The valves maintain residual fuel pressure in the fuel system when the electric fuel transfer pump is not operating. The valves also prevent fuel from flowing in the wrong direction.
Each cylinder has a glow plug in order to aid the cold starting of the engine. The glow plugs are controlled by the Electronic Control Module (ECM).
In cold ambient temperatures, energizing the glow plugs for a time period will heat the cylinder sufficiently for easy starting of the engine.
Refer to Operation and Maintenance Manual, "Cold Weather Starting" for the correct method of starting the engine is cold conditions.