854032 Mercruiser NUT

Illustration 1 g00573299
Flow diagram of the fuel system (1) Fuel injection nozzles (2) Fuel overflow tube (3) Fuel filter (4) Fuel tank (5) Vent plug and check valve (6) Water separator (7) Fuel injection pump housing (8) Fuel transfer and priming pump (9) Screen filter (10) Fuel return lineWater separator (6) is between fuel tank (4) and the fuel transfer and priming pump (8). The water separator removes water from the fuel. The water separator should be drained daily.Fuel enters the transfer pump through a screen filter (9). The screen filter is located in the fitting of the fuel inlet line.Fuel transfer pump (8) directs fuel from fuel tank (4) to fuel filter (3). From fuel filter (3), the fuel enters fuel injection pump housing (7) .The excess fuel that is delivered to the fuel injection pumps and fuel injection nozzles (1) serves the following functions before returning to fuel tank (4) through fuel return line (10) :
Lubrication
Cooling
CleaningThe vent plug and check valve (5) keeps the fuel from draining out of the fuel gallery in order to maintain a fuel supply for engine start-up.The fuel transfer and priming pump (8) delivers fuel from fuel tank (4) to fuel injection pump housing (7). The fuel injection pump camshaft drives the fuel transfer and priming pump (8). The fuel priming pump is used to fill the system after the fuel filter is replaced or when the system has run out of fuel.The fuel flows through fuel filter (3) before entering fuel injection pump housing (7) .Fuel pressure can be checked between the fuel transfer pump and fuel filter (3) by replacing the vent plug with a pressure gauge.The fuel injection pumps are powered by the fuel pump gear which is timed to the engine crankshaft. The fuel pump gear drives the fuel injection pump camshaft. The camshaft activates the six individual fuel injection pumps. There is one fuel injection pump for each piston cylinder in the engine. The six individual fuel injection pumps are contained within fuel injection pump housing (7). The governor controls the amount of fuel that is delivered to the engine cylinders by the individual fuel injection pumps through an injector control rack. The governor is mechanically actuated by a linkage.The shutoff solenoid moves the fuel rack to the Fuel-Off position when the solenoid is energized regardless of the throttle position.Note: Loosen the vent plug in order to prime the fuel injection pump and the fuel injection lines. The system is primed when fuel flows from the air vent plug without air bubbles.Fuel Injection Pump
Illustration 2 g00573408
Cutaway view of fuel injection pump (A) Outlet to fuel injection nozzle (B) Suction and discharge port (1) Stop for delivery valve (2) Delivery valve holder (3) Spring for delivery valve (4) Delivery valve (5) The barrel for the plunger (6) Pump housing (7) Fuel supply chamber (8) Control pinion (9) Injection control rack (10) Pump plunger (11) Control sleeve (12) Plunger spring (13) Driving vane (14) Shims (15) Tappet (16) CamshaftThis is a sectional view of an individual injection pump within the fuel injection pump housing. Plunger spring (12) and tappet (15) force plunger (10) to follow the contour of the rotating camshaft lobe. As camshaft (16) rotates, tappet (15) moves up the camshaft lobe which compresses plunger spring (12). The compressed plunger spring forces pump plunger (10) and driving vane (13) upward. As pump plunger (10) moves up the fuel pressure in the chamber that is above the pump plunger overcomes the force of the spring of delivery valve (3). This fuel pressure delivers fuel to the fuel injection nozzle.The amount of fuel which is delivered from the pump to the fuel injection nozzles is determined by the position of injection control rack (9). The governor controls the injection control rack. Each individual fuel pump is connected to injection control rack (9) through a control pinion (8). The control pinion clamps to control sleeve (11). Driving vane (13) slides up and down in slots inside the control sleeve. The slots in the control sleeve will not allow pump plunger (10) and driving vane (13) to rotate within control sleeve (11). The slots in control sleeve (11) force the pump plunger and the driving vane to rotate with the control sleeve. The movement of injection control rack (9) causes pump plunger (10) and the driving vane to rotate with control sleeve (11) while the plunger barrel remains fixed.Fuel Injection Pump Operation
Illustration 3 g00573300
Components and stages of the fuel injection pump (A) Intake of fuel (B) Start of pumping action (C) Pumping in progress (D) Pumping ends (E) Fuel returns (1) Fuel outlet port (2) Delivery valve (3) Fuel inlet port (4) Control groove (5) Pump cylinder (6) Pump plunger (7) Driving vane (8) Tappet (9) CamshaftA. Intake of Fuel
Fuel is sent from the fuel transfer pump to the fuel injection housing and the fuel is discharged under pressure from the individual fuel injection pumps. The timing of the fuel discharge is determined by the movement of camshaft (9). The fuel from the supply chamber flows in pump cylinder (5) through fuel inlet port (3) when pump plunger (6) is at the bottom center.B. Start of Pumping Action
As camshaft (9) rotates pump plunger (6) moves upward. Pump plunger (6) closes fuel inlet port (3) which pressurizes the fuel. This occurs when the top of the pump plunger reaches the upper edge of fuel inlet port (3) .C. Pumping in Progress
As pump plunger (6) continues to move upward, the pressurized fuel in the pump cylinder pushes up the delivery valve (2). The fuel flows out of fuel outlet port (1) through the fuel line to the fuel injection nozzle.D. Pumping Ends
The pumping of fuel ends when the top edge of