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 TM 9-2815-220-24
THEORY OF OPERATION
0004 00
ENGINE COMPONENTS (Continued)
Intake Manifold Heaters:
The intake manifold, which distributes induction air to each bank of cylinders, is equipped
with an electrically-operated flame-type intake manifold heater. The heater is provided as an
aid for cold weather starting and cold weather operations.
A flow diagram of the manifold air induction heater system is illustrated on the facing page.
Operation of the heater switch (in the vehicle operator's compartment) energizes the manifold
heater fuel solenoid valve, heater ignition unit, and spark plug for each heater simultaneously.
Fuel is hand pumped by the purge pump through the manifold heater fuel filter and fuel
solenoid valve and sprayed into the intake manifold. The fuel ignited by the spark plug, burns
in the intake manifold as the engine is cranking, and the flame heats the incoming air. This
flame-heated air and the products of combustion are fed directly into the cylinders with little
heat loss. The results are immediate engine response assuring complete combustion at low
engine rpm and at no-load operating conditions with low ambient temperatures.
The manifold heater, fuel inlet solenoid valve, prevents fuel pumped by the fuel pump
assembly from entering the air intake manifold heater unless the heater system is energized. A
manifold heater fuel return check valve and solenoid valve are located at the rear of the engine.
The solenoid valve is also energized (opened) when the ignition unit and heater spark plugs are
energized permitting excess fuel to be returned to the fuel tanks. The main fuel backflow
valve prevents back flow of the fuel when the purge pump in the driver's compartment is
actuated.
WP 0004 00-23
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