Fuel System Operation
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| Illustration 1 | g00579357 |
3516 Fuel system schematic | |
The fuel supply circuit uses a fuel transfer pump to deliver fuel from the fuel tank to the fuel injectors. The transfer pump is a fixed displacement gear pump.
The fuel flows from the fuel transfer pump through a fuel filter before entering the fuel supply manifold.
The engine is equipped with an electric fuel priming pump that is located on the fuel filter base. The pumps are used to refill the system after the fuel filters are changed. The system will also be refilled after draining the fuel supply and return manifolds, when the fuel injectors are replaced.
The fuel flows continuously from the fuel supply manifold through the fuel injectors. The fuel flows when either the supply or the fill port in the injector is not closed by the injector body assembly plunger. The fuel is returned to the tank by the fuel return manifold. The fuel that is not injected into the cylinder is displaced by the plunger. Then the fuel is returned to the tank through the fuel return manifold. Refer to the "Fuel Injector" for a complete explanation of the injection process.
A pressure regulating valve is at the end of the fuel return manifold. The pressure regulating valve controls the entire fuel system pressure. This action provides proper filling of the fuel injectors.
Electronic Control Circuit for the Fuel System
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| Illustration 2 | g00290848 |
3516 Fuel system electronic control circuit | |
The electronically controlled mechanically actuated fuel injector system provides total electronic control of injection timing. The injection timing is varied in order to optimize the engines performance. This action is a result of engine operating conditions.
The engine speed is controlled by adjusting the duration of injection. The timing ring is part of the rear gear group which is monitored by the engine speed/timing sensor. The engine speed/timing sensor provides information to the electronic control module (ECM). The ECM uses this information to determine the crankshaft position and the engine speed. This data allows the ECM to send a signal to the injector solenoids. The fuel injectors solenoid is energized in order to begin fuel injection. The fuel injectors solenoid is de-energized in order to end fuel injection. Refer to the "Fuel Injector"
Fuel Injector Mechanism
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| Illustration 3 | g00282693 |
Fuel injector mechanism (1) Adjusting nut (2) Rocker arm assembly (3) Fuel injector (4) Pushrod (5) Cylinder head (6) Camshaft (7) Lifter | |
The fuel injector mechanism provides the downward force that is required to pressurize the fuel in the fuel injector. Mechanically operated electronic fuel injector (3) allows fuel to be injected into the combustion chamber. This injection occurs at the precise time. The camshaft gear is driven by an idle gear which is driven by the crankshaft gear. The camshaft has three lobes for each cylinder. Two lobes operate the inlet and exhaust valves, and one lobe operates the fuel injector mechanism. Force is transmitted from the fuel injector lobe on camshaft (6) through lifter (7) to pushrod (4). From pushrod (4), force is transmitted through rocker assembly (2) and to the top of the fuel injector. Adjusting nut (1) allows setting of the injector lash. Refer to the Testing and Adjusting, "Fuel Injector Adjustment" for proper setting of the injector lash.
Fuel Injector
When the stroke of the plunger is at the top, fuel flows through the low-pressure fuel passages in the body. The fuel then flows to the center passage in the plunger and into the pumping chamber below the plunger. When the stroke of the plunger is at the bottom, fuel flows through the high-pressure fuel passages. The fuel flows through the open cartridge valve and into the low-pressure fuel passages. When the cartridge valve is closed or energized, the fuel flow through the cartridge valve is blocked. This blockage causes a buildup in fuel pressure and injection to begin. Injection continues until the cartridge valve is de-energized or open. Fuel is allowed to flow through the cartridge valve. This action causes the drop in pressure and the stopping of the injection. The plunger continues to force fuel through the open cartridge valve until the stroke of the plunger reaches the bottom. The fuel injector spring returns the plunger to the starting position and the cycle repeats.
The start of fuel injection is determined when the cartridge valve is opened or closed by the Electronic Control Module (ECM) via the injector solenoid. The quantity of fuel that is injected is determined when the cartridge valve is opened or closed.
During the fuel injection stroke, the fuel passes from the pumping chamber through a nozzle valve. The nozzle valve has a spring loaded needle valve. Fuel flows through the fuel passage around the needle valve to the valve chamber. In the valve chamber, the fuel pressure lifts the needle valve away from the seat. The fuel can now flow through the orifices in the tip into the combustion chamber.
The bottom of the injector will protrude for a short distance below the cylinder head into the combustion chamber. The injector tip has several small orifices that are equally spaced around the outside diameter. The orifices spray fuel into the combustion chamber.