TM-9-2815-220-24

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.

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

TM-9-2815-220-24 - Page 85 of 1563