General Operation of the Fuel System
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| Illustration 1 | g00468817 |
(1) Fuel tank (2) Fuel transfer pump (3) Manual fuel shutoff valve (4) Water separator (5) Primary fuel filter (6) Mechanical governed fuel injection pump (7) Fuel injection nozzles (8) Fuel return line from fuel injection nozzle | |
When the engine is cranking, the fuel is pulled from fuel tank (1) by fuel transfer pump (2). The fuel transfer pump forces the fuel through the water separator (4) and the primary fuel filter (5) to the fuel injection pump (6) .
When the fuel goes through the water separator, any water in the fuel will go to the bottom of the bowl. The water can be drained through a valve which is located at the bottom of the bowl. If the engine does not have water separator (4), primary fuel filter (5) functions as a water separator. The primary fuel filter can be drained through a valve that is located at the bottom of the filter housing.
A manually operated fuel shutoff valve (3) is located between the fuel transfer pump and the fuel filter. The fuel can be turned off by this valve in order to change the fuel filters. The fuel should be turned off for most repairs and maintenance of the engine.
The fuel flows from the water separator at low pressure to primary fuel filter (5). The fuel flows at low pressure from the fuel filter to fuel injection pump (6) .
The fuel injection pump sends fuel at high pressure to each fuel injection nozzle (7). 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 |
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 flows through fuel return line (8) to the inlet side of primary fuel filter (5). 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.
Refer to the Systems Operation, Testing and Adjusting Module, "General Information" topic for locations of the components for the fuel system.
The fuel transfer pump has a priming lever that is manually operated in order to remove the air from the fuel system. When the priming lever is moved up and down, pressure is applied to a diaphragm which pumps the fuel.
In order to release air from the fuel injection pump and the fuel injection nozzles, the nuts for the fuel injection nozzles should be loosened. The priming lever is operated until fuel, that is free from air, flows from each connection on the fuel injection nozzles. Refer to the Systems Operation, Testing and Adjusting Module, "Air In Fuel - Test" topic.
Each cylinder has a glow plug. The glow plugs may be activated by one of two methods. The following methods are the two ways of activating the glow plugs:
- A starting aid switch
- An auxiliary position on the ignition switch
When the switch is manually turned on, the glow plug becomes hot. The heat increases the vaporization of the fuel in the cylinder. This condition improves the ease of starting in cold weather. Power to the glow plugs is stopped when the switch is manually turned off.
Governor
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 | g00468237 |
Governor control mechanism in the timing gear case (1) Mechanical stop control (2) Spring (3) Connection for the linkage to the fuel injection pump (4) Control lever (5) Arm | |
The movement of the governor weight assembly is transferred to the fuel rack on the fuel injection pump by control lever (4), arm (5) 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 (5). 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 (1). 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. The excess fuel position aids the cold starting of the engine.
Fuel Injection Pump
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| Illustration 4 | g00746909 |
Fuel injection pump (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: valves for the delivery of fuel, 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.
Fuel Injection Nozzles
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| Illustration 5 | g00691280 |
Fuel injection nozzle for the 3003 Engine (1) Fuel injection nozzle (2) Seal (3) Cap (4) Spacer (5) Gasket | |
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| Illustration 6 | g00701932 |
Fuel injection nozzle for the 3013, 3014 and the 3024 Engines (6) Fuel injection nozzle (7) Gasket | |
Gaskets (5) and (7) help to prevent blowby. The two gaskets and spacer (4) also set the projection of the fuel injection nozzle 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 is installed in the cylinder head, new gaskets (5) and (7) should be installed.
The operating pressure of the fuel injection nozzle is set and tested at the factory. Refer to the Specifications Module, "Fuel Injection Nozzles" topic 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.
Fuel Transfer Pump
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| Illustration 7 | g00749500 |
Components of the fuel transfer pump (typical example) (IN) Fuel flow to the fuel transfer pump (OUT) Fuel flow out of the fuel transfer pump (1) Outlet valve (2) Inlet valve (3) Diaphragm (4) Diaphragm assembly (5) Arm | |
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 (3) prevents the leakage of the fuel into the cylinder block. The diaphragm creates part of the pumping action of the fuel transfer pump. Outlet valve (1) and inlet valve (2) operate as check valves.
A lobe on the camshaft causes arm (5) to move up and down. When the arm moves down, diaphragm assembly (4) moves down. This down movement increases the size of the chamber above the diaphragm assembly. This suction opens inlet valve (2) which draws fuel into the chamber above the diaphragm assembly (IN) .
When the arm moves up, the diaphragm assembly moves up. This up movement pressurizes the chamber above the diaphragm assembly. This pressure opens outlet valve (1) which allows fuel to flow toward the fuel injection pump (OUT) .
Glow Plugs
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. The glow plugs should not be activated for more than 15 seconds continuously.