TM 9-2320-386-10 Change 1 1-14.1 A mechanical governor, transfer pump, and high-pressure unit injection fuel sys- tem provide engine response and fuel economy for ESP vehicles. The transfer pump creates a vacuum that draws fuel from the fuel tank. It then pumps fuel under low pressure to the fuel/water separator where water and contam- inants are removed. Filtered fuel is then carried to the injectors. The injectors use a plunger-and-barrel system to create the high pressures needed for injection. Inside the injector, a spring-loaded needle valve lifts from its seat to allow high pressure fuel to be injected into each cylinder. Excess fuel is routed from the engine cylinder head back to the governor and then to the fuel tank. A fuel shutoff solenoid mounted on the fuel pump cuts the flow of fuel to the injectors when the operator turns the accessory switch off. The ESP vehicles are equipped with a compressed air system that supplies clean dry filtered air to operate air-actuated or assisted accessories throughout the vehi- cle. The air is supplied from engine air compressor through an air dryer and stored in two air reservoirs. The air from reservoirs is piped along frame rails back to two rear couplings. The left side air coupling is the service coupling and is used to supply air to operate trailer brakes. The right side air coupling is the emergency coupling and is used to release spring brakes if trailer is so equipped and to connect an air hose to manual- ly inflate vehicle tires. The air reservoirs also supply air forward to air pressure gauge, two air hydraulic brake boosters, steering assist cylinder, drag link assist, air horns, transfer case air cylinder, front axle engagement switch, and cooling fan actuator and clutch. The CTIS allows the operator to manually select a tire pressure suitable to the terrain being traversed. The system incorporates an Electronic Control Unit (ECU) and air regulating system which provides and maintains the correct air pressure to all tires at the same time. The ECU controls the manifold, which automatically directs compressed air to inflate the tires, or signals the deflation port to deflate the tires according to the operator-selected terrain setting. The ECU monitors and regu- lates air system pressure in 30-minute intervals and compensates for thermal tire pressure changes as recommended by the tire manufacturer. 1-21. CENTRAL TIRE INFLATION SYSTEM (CTIS) OPERATION 1-20.1. COMPRESSED AIR SYSTEM OPERATION 1-20. FUEL SYSTEM OPERATION