General Operation of the Fuel System
Refer to Systems Operation, "General Information" for locations of the components for the fuel system.
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| Illustration 1 | g01103741 |
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Typical example (1) Fuel tank (2) Hand primer (3) Fuel priming pump (4) 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 fuel tank (1) by fuel transfer pump (3). The fuel transfer pump forces the fuel through fuel filter (4) to fuel injection pump (5).
Fuel filter (4) also functions as a water separator. The 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 injection nozzle (6). The fuel injection 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) 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 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 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 timing case.
These engines have a mechanical governor in order to control engine rpm. 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 timing gear case.
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| Illustration 3 | g00822233 |
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Governor control mechanism in the timing gear case (1) Connection for the linkage to the fuel injection pump (2) Mechanical stop control (3) Lever return spring (4) Control lever (5) Start spring (6) Arm (7) Governor adjustment screw | |
The movement of the governor weight assembly is transferred to the fuel rack on the fuel injection pump by control lever (4), arm (6) and the linkage to the fuel injection pump. A spring connects the arm and the control lever. This spring controls the movement of the governor weight assembly on the camshaft. When the angle of the control lever changes, tension on the spring changes. This action controls the linkage to the fuel rack on the fuel injection pump, which controls the engine rpm.
The bolt for the maximum speed adjustment is mounted in the cylinder block. This adjustment limits the movement of arm (6). This adjustment should only be made by personnel with the correct training.
The bolt for the maximum fuel adjustment is mounted in the cylinder block. This adjustment regulates the fuel injection at high engine rpm. This adjustment should only be made by personnel with the correct training.
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.
The fuel injection pump timing, the low idle, and the high idle are preset at the factory. Adjustments to the pump timing, and idle rpm should only be made by personnel which 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.
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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 electric fuel shutoff solenoid 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 timing 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) Gasket | |
Gasket (2) helps to prevent blowby. The gasket 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 gasket (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.
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| Illustration 6 | g00909677 |
The fuel transfer pump 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 diaphragm prevents the leakage of the fuel into the cylinder block. The diaphragm creates part of the pumping action of the fuel transfer pump. The outlet valve and the inlet valve operate as check valves.
A lobe on the camshaft causes the arm to move up and down. When the arm moves down, the diaphragm assembly moves down. This down movement increases the size of the chamber above the diaphragm assembly. This suction opens the inlet valve which draws fuel into the chamber above the diaphragm assembly to the fuel transfer pump "(IN)".
When the arm moves up, the diaphragm assembly moves up. This up movement pressurizes the chamber above the diaphragm assembly. This pressure opens the outlet valve which allows fuel to flow out of the fuel transfer pump toward the fuel injection pump.
Each cylinder has a glow plug in order to aid the cold starting of the engine. The glow plugs may be energized by two different methods:
- The ignition switch is moved to the auxiliary position (if equipped).
- The starting aid switch (if equipped) is moved to the ON position.
Usually, energizing the glow plugs for six seconds will heat the cylinder sufficiently for easy starting of the engine.