TROUBLESHOOTING THE HMMWV - OD1616 - LESSON 1/TASK 1
In the paragraphs that follow, the components that comprise the fuel
system will be discussed in a little more detail.
(1) Fuel Tank. The first component of the fuel system is the fuel
tank.
The fuel tank used on the HMMWV is made out of plastic
(polypropylene).
This protects the fuel tank from small explosive
charges. Another reason for the use of the plastic tank, is that in
a metal fuel tank, such as the one found on your automobile,
condensation or water will form as the fuel level in the tank
decreases and the ambient or outside air temperature changes.
The
tank can hold up to 25 gallons of either diesel fuel 1 (DF1), diesel
fuel 2 (DF2), or diesel fuel arctic (DFA). The fuel tank is located
at the rear of the vehicle, on the right side.
(2) Fuel Pump.
Fuel injection pumps must be supplied with fuel
under pressure for the following reasons.
The injection pumps lack
the suction ability to draw the fuel from the tank by themselves. It
is necessary to supply the fuel to the injection pump in excess, so
that the fuel may be used to cool and lubricate the system before
passing it back to the tank. Also, without a supply pump, the system
would lose its prime whenever the pump is in the nondelivery mode.
The HMMWV uses a cam-driven diaphragm (mechanical) type fuel pump.
This particular type of fuel pump is currently the most popular. The
operation of the pump is as follows:
The rocker arm is moved up and down by the engine camshaft.
The
rocker arm spring causes the rocker arm to follow the cam lobe. The
rocker arm hooks into an elongated slot in the pull rod. The other
end of the pull rod is attached to the diaphragm.
As the camshaft
operates the rocker arm, it will operate the diaphragm against the
pull of the diaphragm spring. As the rocker arm pulls the diaphragm
down, the inlet check valve is unseated and fuel is drawn into the
pump chamber. The outlet check valve seals the outlet passage. As
the diaphragm spring pushes the diaphragm back up, the inlet check
valve seals the inlet and the fuel in the pump chamber is pushed
through the unseated outlet check valve and through the pump outlet.
This operation is repeated each time the rocker arm operates the
diaphragm.
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