8M0031551 Mercury TRIM MOTOR

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Fuel system schematic (1) Fuel tank (2) Fuel return line (3) Priming pump (4) Fuel injector nozzle (5) Fuel injection line (6) Fuel injection pump (7) Primary fuel filter (8) Check valves (9) Fuel transfer pump (10) Secondary fuel filter (11) Constant purge valve (12) Fuel injection pump housingFuel transfer pump (9) pulls fuel from fuel tank (1) through the primary fuel filter (7) and check valves (8). From the fuel transfer pump, the fuel is pushed through secondary fuel filter (10) and to the fuel manifold in fuel injection pump housing (12). A bypass valve in the fuel transfer pump keeps the fuel pressure in the fuel system at 170 to 280 kPa (25 to 40 psi).Constant purge valve (11) allows a constant fuel flow through fuel return line (2) and back to fuel tank (1). The constant purge valve returns approximately 34 L (9 US gal) per hour of fuel and air to the fuel tank. This helps keep the fuel cool and free of air. Fuel injection pump (6) receives fuel from the fuel manifold. Fuel injection pump (6) pushes fuel at a high pressure through fuel line (5) to fuel injector nozzle (4). The fuel injector 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
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Fuel injection pump (1) Inlet Passage (2) Check Valve (3) Bypass port (4) Spill port (5) Scroll (6) Slot (7) Pump plunger (8) Spring (9) Fuel rack (10) Gear (11) Lifter (12) Cam The fuel injection pump consists of six individual injection pumps. The fuel injection pump increases the pressure of the fuel. The fuel injection pump sends a precise amount of fuel to the fuel injection nozzle assembly. The fuel injection pump is moved by cam (12) of the fuel pump camshaft. When the camshaft turns, the cam raises the lifter (11) and the pump plunger (7) to the top of the stroke. The pump plunger always makes a full stroke. As the camshaft turns farther, spring (8) returns the pump plunger and the lifter to the bottom of the stroke.When the pump plunger is at the bottom of the stroke, the fuel transfer pump pressure goes into inlet passage (1). This fuel goes around the pump barrel to the bypass port (3). Fuel then fills the area above the pump plunger.The upward stroke of the pump plunger will push fuel out of the bypass port. Fuel pushes out until the top pump plunger closes the port. As the pump plunger moves up, the pressure of the fuel increases. This allows fuel to flow through the fuel injection line to the fuel injector nozzle. As the pump plunger continues to move upward, scroll (5) uncovers spill port (4). The fuel above the pump plunger travels through slot (6). The fuel continues along the edge of scroll (5), out spill port (4) and back to the fuel manifold. This is the end of the injection stroke. The pump plunger may continue to travel upward, but more fuel will not flow to the fuel injector nozzle.When the plunger travels downward, this uncovers closed bypass port (3). The fuel begins to fill the area above the pump plunger again, and the pump is ready to begin another stroke.The rotation of the pump plunger controls the amount of fuel that is received by the fuel injector nozzle. Gear (10) is attached to the pump plunger. The gear meshes with the fuel rack (9). The governor moves the fuel rack according to the fuel requirements of the engine. The governor moves the fuel rack (9). The fuel rack turns the pump plunger (7). Fuel flows through the bypass port (3) into the spill port (4). As the distance increases between pump plunger (7), and spill port (5), the greater quantity of fuel will be injected .To stop the engine, the pump plunger is rotated so that slot (6) is in line with spill port (4). Fuel flows out of the spill port. Fuel will not flow to the fuel injector nozzle. Fuel Injector Nozzle
The fuel injector nozzle is installed through the cylinder head into the combustion chamber. The fuel injection pump sends high pressure fuel to the fuel injector nozzle. Then, the fuel is made into a fine spray for good combustion.
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Fuel injector nozzle (1) Carbon dam (2) Seal (3) Passage (4) Filter screen (5) Orifice (6) Valve (7) Diameter (8) Spring Seal (2) is positioned against the cylinder head. This prevents leakage of compression from the cylinder. Carbon dam (1) keeps carbon out of the bore of the cylinder head. Fuel with high pressure from the fuel injection pump flows into the inlet passage. Fuel then flows through filter screen (4) and into passage (3). The fuel continues to the area below diameter (7) of valve (6). The fuel pressure increases on the diameter (7). The fuel pressure exceeds the spring pressure (8). The valve (6) rises. This occurs when fuel pressure rises above valve opening pressure. The tip of the valve is removed from the nozzle seat. Fuel flows through orifice (5) and into the combustion chamber.The injection of fuel continues until the fuel pressure decreases against diameter (7). The fuel pressure decreases below the pressure of spring (8). Spring (8) forces valve (6) against the nozzle seat. This stops the flow of fuel to the combustion chamber. The fuel injector nozzle cannot be disassembled and no adjustments can be made.Fuel Transfer Pump
The fuel transfer pump is a piston pump. The fuel transfer pump is operated by an eccentric cam for the fuel injection pump. The fuel injection pump is located on the bottom side of the fuel injection pump housing.
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Downward stroke for the fuel transfer pump. The arrows are for fuel flow direction. (1) Pushrod (2) Piston (3) Outlet check valve (4) Pump check valve (5) Pumping spring (6) Pump inlet port (7)