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| Illustration 1 | g00987171 |
Flow diagram of the fuel system (1) Fuel injection nozzles (2) High-pressure fuel lines (3) Fuel return lines (4) Fuel injection pump (5) Fuel supply line (6) Return line to the fuel tank (7) Fuel transfer pump (8) Fuel filter/water separator (9) Fuel tank | |
The engine is equipped with an axial piston distributor injection pump that is mechanically governed.
The axial piston distributor injection pump generates injection pressure for all cylinders in a single pump. The injection pump is responsible for the distribution of fuel to the fuel injection nozzles. The injection pressure is generated by an axially moving piston. The movement of the piston is parallel to the fuel injection pump shaft.
When the engine is cranking, the fuel is pulled from fuel tank (9) through the primary fuel filter/water separator (8) by fuel transfer pump (7) . When the fuel passes through the water separator, any water in the fuel will go to the bottom of the bowl. From the fuel transfer pump, the fuel passes through fuel supply line (5) to fuel injection pump (4) .
The fuel is drawn by an internal fuel transfer pump into the fuel injection pump. The fuel is drawn by an internal fuel transfer pump at a pressure of 48 to 83 kPa (7 to 12 psi). A portion of the fuel is routed through the pressure regulator assembly to the suction side of the fuel injection pump. The fuel that is under pressure from the fuel transfer pump flows to the interior of the pump housing. The pressurized fuel is routed to the pumping chamber. As the plunger rotates and as the plunger reciprocates, high-pressure fuel is routed through high-pressure fuel lines (2) to fuel injection nozzles (1) .
The fuel injection nozzles spray atomized fuel into the cylinder. Excess fuel is routed through fuel return lines (3) and (6) and returned to the fuel tank.
Routing excess fuel back to the fuel tank allows air in the fuel to flow back to the fuel tank through the fuel return line. The fuel that flows into the housing of the fuel injection pump performs the following functions:
- Lubricate the internal components.
- Cool the internal components.
- Remove small air bubbles.
The fuel injection pump needs fuel for lubrication. The precision parts of the pump are easily damaged. The engine must not be started until the fuel injection pump is full of fuel. The system must be primed when any part of the system is drained of fuel. The fuel system needs priming when a fuel filter is changed, and/or when a fuel line is removed, and/or when the fuel injection pump is replaced.
Fuel Injection Pump
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| Illustration 2 | g00992842 |
Components of the fuel injection pump (typical example) (1) Control lever (2) Flyweights (3) Screw for adjusting the full load setting (4) Drive shaft (5) Governor lever (6) Fuel shutoff solenoid (7) Head of the distributor (8) Control sleeve (9) Transfer pump (10) Holder for the rollers (11) Plunger (12) Cam (13) Timer (14) Plunger spring (15) Delivery valve | |
The fuel injection pump is a pressurized system that is 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 correct timing 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 fuel lines to the fuel injection nozzles are equal lengths. This ensures even pressure and correct injection timing at each fuel injection nozzle.
During operation, extra fuel is used as coolant and lubricant for pump parts that move. The extra fuel is circulated through the pump housing. The extra fuel is then returned to the fuel tank. Fuel return lines also carry away any air that is trapped in the fuel injection nozzles or in the fuel injection pump housing.
Fuel Delivery
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| Illustration 3 | g00531644 |
Cross section view of the fuel injection pump (typical example) (4) Drive shaft (6) Fuel shutoff solenoid (8) Control sleeve (12) Cam (14) Plunger spring (15) Delivery valve (16) Gear | |
The fuel injection pump transfers fuel to the fuel injection nozzles at high pressure. Cam (12) is driven from the engine by drive shaft (4) . The drive shaft is driven from the front gear group. Lobes on the cam cause the plunger to reciprocate. The reciprocating motion first draws the fuel into the pump. The reciprocating motion then pressurizes the fuel.
The plunger also rotates with the cam in order to sequentially align the discharge groove of the cam with each of the ports on the fuel injection pump. The plunger moves a distance which is established by the lobes of the cam.
The effective stroke is established by the position of the control sleeve. When control sleeve (8) is moved to the left prior to the injection of fuel, the spill port is uncovered. Uncovering the spill port reduces the amount of fuel that is delivered to the cylinder. When the control sleeve is moved to the right prior to the injection of fuel, the spill port is covered. Covering the spill port increases the amount of fuel that is delivered to the fuel injection nozzle.
The pump also includes an internal timer (not shown). The timer allows early fuel injection by advancing the plunger. The plunger is advanced in relation to the camshaft. Fuel shutoff solenoid (6) is normally closed. When a voltage is applied, the plunger in the solenoid moves up in order to allow the fuel delivery which allows the engine to run.
Timing Control System (if equipped)
The timing control system deactivates the load sensing timer when the engine coolant temperature is below 60 °C (140 °F) or when the pump is used at high altitudes.
Fuel Injection Nozzles
Naturally Aspirated Engines (Indirect Injection)
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| Illustration 4 | g00993073 |
Cross section of the fuel injection nozzle (1) Fuel inlet (2) Body (3) Fuel return (4) Retaining nut (5) Pressure spring (6) Nozzle tip assembly | |
The fuel injection pump forces the fuel to flow under high pressure to the hole in fuel inlet (1) . The fuel then flows down through body (2) to the underside of the needle in nozzle tip assembly (6) . The pressure of the fuel pushes the needle valve and pressure spring (5) . When the force of the fuel pressure is greater than the force of the pressure spring, the needle valve will lift up.
When the needle valve opens, fuel under high pressure will flow through the single orifice and into the cylinder. The fuel is injected into the cylinder as a very fine spray. When the fuel is injected into the cylinder, the force of the fuel pressure in the nozzle body will decrease. The force of the pressure spring will then be greater than the force of the fuel pressure that is in the nozzle body. The needle valve will move quickly to the closed position.
The seat of the needle valve has a close fit with the inside of the nozzle. This makes a positive seal when the valve is closed.
When the fuel is injected into the cylinder, a small quantity of fuel will leak into the chamber that contains the pressure spring. This fuel lubricates the moving parts of the fuel injection nozzle. This fuel then goes through a passage in the body of the fuel injection nozzle to fuel return (3) . This excess fuel is then returned to the fuel tank.
Turbocharged Engines (Direct Injection)
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| Illustration 5 | g00993074 |
Cross section of the fuel injection nozzle (1) Fuel inlet (2) Fuel return (3) Body (4) Pressure spring (5) Retaining nut (6) Nozzle tip | |
The fuel injection pump forces the fuel to flow under high pressure to the hole in fuel inlet (1) . The fuel then flows down through body (3) to the underside of the needle in nozzle tip (6) . The pressure of the fuel pushes the needle valve and pressure spring (4) . When the force of the fuel pressure is greater than the force of the pressure spring, the needle valve will lift up.
When the needle valve opens, fuel under high pressure will flow through the multiple orifices in the nozzle tip and into the cylinder. The fuel is injected into the cylinder as a very fine spray. When the fuel is injected into the cylinder, the force of the fuel pressure in the nozzle body will decrease. The force of the pressure spring will then be greater than the force of the fuel pressure that is in the nozzle body. The needle valve will move quickly to the closed position.
The seat of the needle valve has a close fit with the inside of the nozzle. This makes a positive seal when the valve is closed.
When the fuel is injected into the cylinder, a small quantity of fuel will leak into the chamber that contains the pressure spring. This fuel lubricates the moving parts of the fuel injection nozzle. This fuel then goes through a passage in the body of the fuel injection nozzle to fuel return (2) . This excess fuel is then returned to the fuel tank.