TM 5-3805-258-24-1ENGINEFUEL SYSTEMWhen the pump plunger is at the bottom of thestroke, fuel at transfer pump pressure goes into inletpassage (2), around pump barrel (4) and to bypassclosed port (5). Fuel fills the area above the pumpplunger.After the pump plunger begins the up stroke, fuelwill be pushed out the bypass closed port until the topof the pump plunger closes the port. As the pumpplunger travels farther up, the pressure of the fuelincreases. At approximately 690 kPa (100 psi),check valve (1) opens and lets fuel flow into the fuelinjection line to the fuel injection nozzle. When thepump plunger travels farther up, scroll (9) uncoversspill port (10). The fuel above the pump plunger goesthrough slot (7), along the edge of scroll (9) and outspill port (10) back to fuel manifold (3). This is theend of the injection stroke. The pump plunger canhave more travel up, but no more fuel will be sent tothe fuel injection nozzle.FUEL INJECTION PUMP1 . C h e c k v a l v e . 2 . I n l e t p a s s a g e . 3 . F u e l m a n i f o l d . 4 .Pump barrel. 5. Bypass closed port. 6. Pump plunger. 7.Slot. 8. Spring. 9. Scroll. 10. Spill port. 11. Lifter. 12. Fuelrack. 13. Gear. 14. Cam.When the pump plunger travels down and un-covers bypass closed port (5), fuel begins to fill thearea above the pump plunger again, and the pump isready to begin another stroke.The amount of fuel the injection pump sends to theinjection nozzle is changed by the rotation of thepump plunger. Gear (13) is attached to the pumpplunger and is in mesh with fuel rack (12). Thegovernor moves the fuel rack according to the fuelneeds of the engine. When the governor moves thefuel rack, and the fuel rack turns the pump plunger,SYSTEMS OPERATIONscroll (9) changes the distance the pump plungerpushes fuel between bypass closed port (5) and spillport (10) opening. The longer the distance from thetop of the pump plunger to the point where scroll (9)uncovers spill port (10), the more fuel will beinjected.To stop the engine, the pump plunger is rotated sothat slot (7) on the pump plunger is in line with spillport (10). The fuel will now go out the spill port andnot to the injection nozzle.FUEL INJECTION NOZZLEThe fuel injection nozzle goes through the cylinderhead into the combustion chamber. The fuel injec-tion pump sends fuel with high pressure to the fuelinjection nozzle where the fuel is made into a finespray for good combustion.FUEL INJECTION NOZZLE1. Carbon dam. 2. Seal. 3. Spring. 4. Filter screen. 5. Inletpassage. 6. Orifice. 7. Valve. 8. Diameter. 9. Passage.Seal (2) goes against the cylinder head and pre-vents leakage of compression from the cylinder. Car-bon dam (1) keeps carbon out of the bore in thecylinder head for the nozzle.Fuel with high pressure from the fuel injectionpump goes into inlet passage (5). Fuel then goesthrough filter screen (4) and into passage (9) to thearea below diameter (8) of valve (7). When the pres-sure of the fuel that pushes against diameter (8)becomes greater than the force of spring (3), valve(7) lifts up. When valve (7) lifts, the tip of the valvecomes off of the nozzle seat and the fuel will gothrough the nine 0.20 mm (.008 in.) orifices (6) intothe combustion chamber.The injection of fuel continues until the pressure offuel against diameter (8) becomes less than the forceof spring (3). With less pressure against diameter(8), spring (3) pushes valve (7) against the nozzleseat and stops the flow of fuel to the combustionchamber.3-4
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