THEORY OF OPERATION
ENGINE AND FUEL SYSTEM
Engine Electronic Control Module (ECM)
The engine electronic control module (ECM) provides reference voltages to sensors and switches to monitor
engine and machine operating conditions. The engine ECM processes that information to adjust engine controls
for optimal engine operation. The engine ECM has a self-diagnostic capability which allows it to alert the operator
to any faults or out of range conditions. Diagnostic fault codes can be retrieved by the electronic technician (ET)
over a data link. Diagnostic fault codes can also be retrieved using on-board diagnostics on the instrument cluster.
Low Pressure Fuel System
The low pressure fuel supply circuit supplies a constant supply of clean, air-free, pressurized fuel to the high
pressure fuel system. Fuel is drawn from the fuel tank by the transfer pump. The fuel transfer pump is part of the
fuel injection pump and is not serviced separately. Fuel flows from the fuel tank through the fuel cooler to the
primary fuel filter with water separator. The primary fuel filter with water separator removes large debris and water
from the fuel. The primary fuel filter with water separator base also houses an electric fuel prime pump. The fuel
prime pump is used to remove air from the fuel system when the machine runs out of fuel or when the fuel system
is serviced. The fuel then flows through the transfer pump to the engine ECM. The fuel cools the engine ECM. Fuel
then flows through the secondary fuel filter. The secondary fuel filter removes small impurities and any air from the
fuel. The fuel then flows through the third fuel filter to the fuel injection pump.
High Pressure Fuel System
Clean, air-free, low pressure fuel is supplied to the fuel injection pump by the low pressure fuel supply system. The
fuel injection pump supplies high pressure fuel to the fuel rail. The engine ECM monitors fuel rail pressure and
controls a solenoid on the fuel injection pump to maintain desired pressure. High pressure fuel is constantly
available to the fuel injectors. Fuel pressures in the high pressure fuel system are 10,153-18,855 PSI (70-130
The engine ECM controls the amount of fuel that is injected by varying the signal to each of the fuel injectors. The
fuel injectors will inject fuel only while the fuel injector solenoid is energized. By controlling the timing of the signal,
the engine ECM controls fuel injection timing. By controlling the duration of the signal, the engine ECM controls the
amount of fuel that is injected. Leak-off fuel from the fuel injectors returns to the pressure side of the transfer pump
through a passage in the cylinder head.
Glow Plug System
The glow plug system is used to aid in cold starts. The glow plugs are controlled by the engine ECM. When
temperatures dictate, the engine ECM will provide a ground signal to the glow plug relay. The glow plug relay will
energize and provide power to the glow plugs.