TM 9-2350-256-20-1
UNIT MAINTENANCE
RECOVERY VEHICLE, FULL TRACKED: MEDIUM, M88A1
NSN 2350-00-122-6826, EIC AQA
MANIFOLD AIR INDUCTION HEATER SYSTEM THEORY OF OPERATION
Manifold Air Induction Heater System
The left and right intake manifolds (6 and 9), which distribute supercharged air into each bank of cylinders, are equipped with
electrically ignited intake manifold air heaters (2 and 8). The heaters are provided to facilitate engine starting during cold
weather.
The purge pump is operated to obtain 90 psi (621 kPa) in the manifold heater fuel lines. Operation of the heater switch on
the purge pump handle energizes the manifold heater fuel inlet solenoid valve to allow fuel flow to the heater nozzle. The
heater switch also energizes the high-tension coil creating an electrical spark in the manifold, thereby igniting the sprayed fuel.
Continued operation of the purge pump is required to maintain fuel pressure and an effective spray pattern into the manifold.
A leakoff line is provided to prevent nozzle fouling and is routed into the injector fuel return line. The fuel is burned in the intake
manifold by the ignition of the heater spark plug, which flame-heats the incoming air. This flame-heated air and the products of
combustion are fed directly into the cylinders.
The purge pump line connects to a fuel check and pressure relief valve (14) and pressure regulator valve (see item 20, Figure 1,
WP 0005 00) in the engine. The fuel check and pressure relief valve prevents purged fuel from returning to the tank or to the
purge inlet line.
The fuel check and pressure relief valve (14) ensures the necessary fuel pressure to operate the flame heater spray nozzles (5 and
10). A manifold heater fuel supply solenoid valve (7) and fuel return solenoid valve (16) close the flame heater fuel lines when
the flame heater switch is off.
The manifold heater fuel return solenoid valve (16) is located at the rear of the engine. The valve is energized at the same time
the ignition unit and heater spark plugs are energized and acts as a check valve to prevent fuel returning from the injector pump
and nozzles from entering the heater fuel tubes.
Figure 1. Manifold Air Induction Heater System.
END OF WORK PACKAGE
0006 00-1/2 blank
