TM 5-2410-241-23-1
0004
FUEL SYSTEM CONTINUED
Low Pressure Fuel System
0004
The low pressure fuel system supplies fuel from the fuel tank to the injectors and has three basic functions.
It supplies fuel to:
The injectors for combustion
The injectors for cooling
The fuel system in order to remove air
The major parts of the low pressure fuel system are:
Fuel tank
Fuel transfer lines
Primary fuel filteror water separator
Fuel transfer pump
Secondary fuel filter
Fuel priming pump
Fuel pressure regulator valve
The electronic unit injectors, the engine ECM, sensors, and actuators are also part of the low pressure fuel system.
In the low pressure fuel system, the fuel is pulled from the fuel tank to the primary fuel filter water separator. The
primary fuel filter removes large debris from the fuel before the fuel flows into the transfer pump.
The fuel transfer pump is a gear pump that contains a pressure relief valve. Fuel flows from the outlet port of the
transfer pump to the secondary fuel filter. The 2 micron secondary fuel filter removes small abrasive contaminants
from the fuel system, which can cause damage to the unit injectors.
The primary fuel filter base contains a hand-operated fuel priming pump, which removes air from the system when
a fuel filter has been changed or a unit injector has been changed. The priming pump pulls fuel from the tank to the
transfer pump. The transfer pump pushes fuel through the secondary fuel filter to the supply passage in the
cylinder head and back to the tank.
The fuel pressure regulator consists of a check valve that is spring loaded. The pressure relief valve opens at
approximately 60 to 125 psi (414 to 862 kPa). When the engine is off and the fuel pressure drops below 60 psi, the
check valve closes in order to prevent the fuel in the cylinder head from draining back into the fuel tank. Retaining
the fuel in the head maintains a supply of fuel for the injectors during start-up.
The engine ECM controls major engine functions. Sensors are electronic devices that monitor engine performance
parameters. The pressure sensor, the temperature sensor, and the speed sensor provide information to the engine
ECM by a signal voltage. Actuators are electronic devices, which use electrical currents from the engine ECM to
change engine performance. An example of an actuator is an injector solenoid.
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