Engine Construction and Operation.

Troubleshoot The High Mobility Multi- Purpose Wheeled Vehicle (HMMWV)
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(5) Fuel Injectors. For proper engine performance, the fuel must

be injected into the combustion space in a definite spray pattern.

This is accomplished by the fuel injector.

The fuel enters the nozzle holder body through the high-pressure

inlet. It then passes down to the pressure chamber above the valve

seat. When the pressure developed by the injection pump exceeds the

force exerted by the pressure adjusting spring, the nozzle valve will

be lifted off of its seat, resulting in the injection of fuel into

the cylinder. The valve on the HMMWV will open at approximately 1960

psi.

A controlled seepage exists between the lapped surfaces of the nozzle

valve and its body to provide for lubrication. This leakage/overflow

passes around the spindle and into the pressure adjusting spring

chamber.

From here, the fuel leaves the injector through the

overflow outlet and finally to the overflow lines, which lead back to

the low-pressure fuel supply.

(6) Fuel Supply and Return Line(s). The final two components of

the fuel system are the fuel supply and the fuel return lines. The

fuel supply line is the line that the fuel travels through on its way

from the fuel tank to the various other components of the fuel

system.

The fuel return line is the line that the unused fuel

travels through on its way back to the fuel tank from the injection

pump.

Engine Construction and Operation.

In many respects, the four-

stroke cycle gasoline engine and the four-stroke cycle diesel engine

are very similar. They both follow an operating cycle that consists

of intake, compression, power, and exhaust strokes. They also share

the same system for intake and exhaust valves. The major differences

between gasoline and diesel engines will be discussed in the

paragraphs that follow.

(1) The fuel and air mixture is ignited by the heat generated by

the compression stroke in a diesel engine versus the use of a spark

ignition system on a gasoline engine.

The diesel engine needs no

ignition system. For this reason, the gasoline engine is referred to

as a spark ignition engine, while the diesel engine is referred to as

a compression ignition engine.