THEORY OF OPERATION Continued
The M548A1 fuel compartment is located at the rear of the carrier under the cargo compartment deck. Two electric fuel
pumps supply fuel through fuel supply lines from the fuel compartment to an air separator tank. From the air separator tank,
the engine fuel pump draws the fuel through the primary fuel filter. The engine fuel pump forces the fuel through the
secondary fuel filter to the engine fuel injectors. It then returns surplus fuel through the air separator tanks and fuel return
lines to the fuel compartment. Fuel for the air box heater is drawn from the secondary fuel filter. Quick disconnect fuel
couplings are used to connect the supply and return lines to the engine. The fuel compartment is filled through a fuel filler at
the left rear of the carrier and is drained through a fuel drain under the center tailgate hinge. The entire system is vented by
tubes located at the right rear corner of the carrier and the fuel filler tube.
The air box heater preheats air entering the engine cylinders with an electric air pump, fuel pump, and igniter. This improves
fuel ignition at low temperatures. Fuel is sprayed into the cylinder block air box and ignited to preheat incoming air.
The M548A3 fuel compartment and components are similar to M548A1. Only the front of carrier and its components are