Fuel Flow
 | |
| Illustration 1 | g01246314 |
Fuel system schematic (1) Secondary fuel filter base (2) Fuel injection pump housing (3) Pressure regulating valve (4) Fuel injection line (5) Fuel injection nozzle (6) Fuel return line (7) Electronic control module (ECM) (8) Fuel transfer pump (9) Fuel priming pump (10) Primary fuel filter (11) Fuel tank | |
Fuel transfer pump (8) pulls fuel from fuel tank (11) through the primary fuel filter (10) .
Note: When the engine has reached the normal operating temperature, the inlet fuel temperature to the transfer pump must not exceed 65°C (149°F). Fuel temperatures that are above 65°C (149°F) will reduce the life of the electronics within the ECM. High fuel temperatures will also reduce the life of the transfer pump check valves. Also, high fuel temperatures will reduce engine power output. If the engine is equipped with auxiliary fuel heaters, make sure that the fuel heaters are turned OFF in warm weather operating conditions.
From the fuel transfer pump, (8) the fuel is pushed through the ECM (7). This will keep the electric circuits cool. The cooling plate for the control module is a one piece die cast aluminum housing. The manifolds on the top and the bottom of the control module route fuel from the transfer pump through the cooling plate.
The fuel flows from the ECM through the secondary fuel filter. The fuel flows from the secondary fuel filter to the fuel manifolds in the fuel injection pump housing (2) .
The fuel manifolds supply fuel for each fuel injection pump. A pressure regulating valve allows a constant fuel flow through the fuel return line (6) and back to fuel tank (11). The pressure regulating valve controls the pressure in the manifolds. Also, the pressure regulating valve controls the amount of fuel that goes back to the fuel tank (11). The constant flow of fuel back to the tank removes air from the system.
Individual fuel injection lines carry fuel from the fuel injection pumps to each cylinder. One section of line connects between the fuel injection pump and an adapter that is located on the valve cover base. Another section of line connects between the adapter and the fuel injection nozzle that is located inside the valve cover base.
The fuel transfer pump (8) is installed on the opposite side of the rotary servo pump on the end of the fuel injection pump. The fuel transfer pump has a pressure relief valve. The fuel transfer pump also has a bypass valve. The pressure relief valve controls the maximum pressure of the fuel to the fuel injection pump housing. When the pressure gets too high, the relief valve opens. This directs the fuel back to the inlet side of the transfer pump. The bypass valve allows the fuel to go around the transfer pump gears when the fuel priming pump (9) is used.
When there is air on the inlet side of the system, the fuel priming pump (9) is used before the engine is started. The fuel priming pump is used to fill the low pressure side of the fuel system from the fuel tank. The fuel priming pump moves fuel through the low pressure side of the system. The movement of the fuel removes air from the lines and from components. The fuel then returns to the fuel tank.
A purge orifice or valve is not installed on the fuel injection pump to vent air from the high pressure part of the fuel system. Air that is trapped in the fuel injection lines can be vented. Loosen all of the nuts for the fuel injection lines. The nuts are connected to the adapters in the valve cover base. Move the governor lever to the low idle position. Crank the engine with the starting motor until fuel comes from the fuel line connections. There should be no air in the fuel. Tighten the fuel line nuts. This procedure is necessary because the fuel priming pump will not create enough pressure in order to push fuel through the reverse flow check valves that are located in the fuel injection pump bonnets.
The fuel injection pumps are in time with the engine. The fuel injection pumps send fuel at a very high pressure to the fuel injection nozzles. The fuel injection nozzle contains very small holes in the tip. The small holes change the flow of fuel to a very fine spray. This fine spray improves the fuel combustion in the cylinder.
Fuel Injection Pump
 | |
| Illustration 2 | g01246316 |
Cross section of the fuel injection pump housing (typical example) (1) Fuel manifold (2) Inlet passage (3) Pressure relief passage (4) Check valve (5) Pump plunger (6) Spring (7) Gear (8) Fuel rack (left) (9) Lifter assembly (10) Camshaft | |
The fuel injection pump is moved by the cam of the fuel pump camshaft (10). When the camshaft turns, the cam raises lifter assembly (9) and pump plunger (5) to the top of the stroke. The pump plunger always makes a full stroke. The force of springs (6) hold lifters against the cams of the camshaft. As the camshaft turns farther, spring (6) returns the following components to the bottom of the stroke:
- Pump plunger
- Lifter assembly
The shape of the pump housing is similar to the engine cylinder block. There are six pumps on each side.
When the pump plunger is at the bottom of the stroke, fuel from fuel manifold (1) flows into inlet passage (2). Fuel fills in the area above the pump plunger (5). As the plunger moves up, the inlet passage closes.
The pressure of the fuel in the chamber above the plunger increases until the pressure is high enough to cause check valve (4) to open. Fuel under high pressure flows out of the check valve. Fuel flows through the fuel line to the fuel injector nozzle, until the inlet passage opens into pressure relief passage (3) in the plunger. The pressure in the chamber decreases and the check valve closes.
A greater amount of fuel is forced through check valve (4), when inlet passage (2) remains closed. The pressure relief passage (3) controls the amount of time that the inlet passage is closed. The following items determine the amount of time that the inlet passage is closed.
- Design of the inlet passage
- Rotation of the plunger
The governor moves the fuel rack (8) according to the engine's need for fuel. The fuel rack moves the gear (7) that is fastened to the pump plunger (5). This causes a rotation of the plunger.
7000 Series Fuel Injection Nozzles
The fuel injection nozzle is installed into an adapter through the cylinder head into the combustion chamber. The fuel injection pump sends fuel with high pressure to the fuel injection nozzle. Then, the fuel is made into a fine spray for good combustion.
 | |
| Illustration 3 | g01246318 |
Fuel injection nozzle (1) Carbon dam (2) Seal (3) Passage (4) Filter screen (5) Inlet passage (6) Orifice (7) Valve (8) Diameter (9) Spring | |
Seal (2) is positioned against the nozzle adapter. This prevents leakage of compression from the cylinder. Carbon dam (1) keeps carbon out of the bore in the nozzle adapter.
Fuel with high pressure from the fuel injection pump flows into the inlet passage (5). Fuel then flows through filter screen (4) and into passage (3). The fuel continues to the area below diameter (8) of valve (7). When the fuel pressure against diameter (8) becomes greater than the force of spring (9), valve (7) lifts up.
Valve (7) lifts up when the fuel pressure rises above the valve opening pressure of the fuel injection nozzle. When valve (7) lifts up, the tip of the valve comes off the nozzle seat, and the fuel will flow through the orifices (6) into the combustion chamber.
The injection of fuel continues until the pressure of fuel against diameter (8) becomes less than the force of spring (9). With less pressure against diameter (8), spring (9) pushes valve (7) against the nozzle seat. This stops the flow of fuel to the combustion chamber.
Note: The fuel injection nozzle cannot be disassembled, and no adjustments can be performed.