TM-9-2815-200-35 Maintenance Manual for AVDS-1790-2M AVDS-1790-2A and AVDS-1790-2AM Engines Download
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b. Intake Manifold Heater (fig. 1-12). (1) The intake manifold (figs. 1-1 and 1-5) 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. Operation of the heater switch (in the vehicle operator’s compartment) energizes the manifold heater fuel solenoid valve, the heater ignition unit, and spark plug for each heater simultaneously. Fuel is hand pumped through the manifold heater fuel filter and fuel solenoid valve and sprayed into the intake manifold. The fuel is ignited by the spark plug and 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. This results in an immediate engine response, and assures com- plete combustion at low engine rpm and at no- load operating conditions with low ambient temperature. (2) 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 solenoid valve is located at the rear of the engine. The valve is also energized (opened ) when the ignition unit and heater spark plugs are energized to permit excess fuel to be returned to the fuel tanks. The main fuel check valve prevents back flow of the fuel when the purge pump in the driver’s com- partment is actuated. 1-20. Exhaust System and Tur- bosupercharger a. The exhaust system consists of four manifolds, one for each group of three adjacent cylinders. The two exhaust manifolds on each cylinder bank are connected to the tur- bosupercharger on their respective side of the engine. b. Exhaust gases from each side of the engine enter a turbosupercharger and are forced around a turbine housing, radially inward, and through a nozzle ring, toward the turbine wheel. The exhaust gases drive the turbine wheel which in turn, drives the compressor wheel since both wheels are on a common shaft. Intake manifold air enters at the center of the compressor wheel and flows radially outward through a diffuser section into the compressor housing. The air at increased velocity then leaves through a tangential outlet on the outside of the compressor housing, and enters the intake manifold. c. The exhaust gases are expelled from the turbosuperchargers into the vehicle exhaust system. 1-21. Cooling System Note. The key letters shown below in parentheses refer to figure 1-8. a. Fans. The top of the engine is shrouded to house two cooling fans (WW and NN) which draw cool air from the underside of the engine, through the cylinder fins, and discharge the hot air vertically from the top shroud. The fans are attached to adapters (MM) and are mounted on shafts which are driven through a fan drive clutch assembly (LL). The rear fan clutch is driven by the rear fan drive shaft (GG), fan drive bevel gearshaft (FF), and fan driven gearshaft (HH). The front fan clutch is driven by the front fan drive shaft (EE ) and another fan driven gearshaft (HH). 1-17