Fuel Injection

TM 9-2320-312-24-2

Troubleshooting Section

The personality module inside the ECM sets certain

limits on the amount of fuel that can be injected.

The "FRC Fuel Limit" is a limit that is based on the

boost pressure. The "FRC Fuel Limit" is used to

control the air/fuel ratio for control of emissions.

When the ECM senses a higher boost pressure,

the ECM increases the "FRC Fuel Limit". A higher

boost pressure indicates that there is more air in the

cylinder. When the ECM increases the "FRC Fuel

Limit", the ECM allows more fuel into the cylinder.

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Illustration 2

The ECM knows the cylinder position for timing

because of the signal from the engine speed/timing

sensors. The ECM adjusts timing for best engine

performance, for fuel economy, and for the control

of white smoke. Actual timing and desired timing

cannot be viewed with the electronic service tool.

The ECM determines the location of top center of

the number one cylinder from the signal that is

provided by the engine speed/timing sensors. The

ECM decides when injection should occur relative

to top center. The ECM then provides the signal to

the injector at the desired time.

Fuel Injection

The ECM controls the amount of fuel that is injected

by varying the signals to the injectors. The injectors

will pump fuel only if the injector solenoid is

energized. The ECM sends a high voltage signal

in order to energize the solenoid. The injector

solenoid unseats the poppet valve. The oil path

to the drain passage will close while the inlet oil

passage opens for the high pressure oil. The high

pressure oil enters the injector and pushes on the

intensifier piston. This causes the fuel pressure to

increase. The diesel fuel is then injected into the

combustion chamber. By controlling the timing and

the duration of the high voltage signal, the ECM can

control injection timing and the ECM can control the

amount of fuel that is injected.

The ECM controls the fuel pressure that is injected

into the cylinder by controlling the injection actuation

pressure control valve. The output pressure of the

injection actuation pressure control valve is a dump

valve that is controlling the output pressure of the

high pressure oil pump.