TM 5-2410-240-23-1
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ENGINE SYSTEMS CONTINUED
Engine Speed Governor
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This electronic control determines injection timing, the amount of fuel delivered to the cylinders, and inlet manifold
pressure. Actual and desired conditions drive changes to these outputs.
The governor's software compares desired engine speed to actual engine speed. If desired engine speed is
greater than actual engine speed, the governor will inject more fuel in order to increase engine speed. The primary
speed/timing sensor and secondary speed/timing sensor provide actual engine speed data to the engine ECM.
Timing Considerations
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Once the governor determines the amount of fuel to deliver to the cylinders, the software must then determine fuel
injection timing. The engine ECM uses input from the engine coolant temperature sensor, the inlet manifold
temperature sensor, and the inlet manifold (boost) pressure sensor to determine fuel injection timing.
At engine start-up, the engine ECM determines the top center position of the number 1 cylinder based on data from
the secondary speed/timing sensor. The engine ECM decides when fuel injection should occur relative to the top
center position. The engine ECM optimizes engine performance by control of each of the electronic unit injectors
so that the required amount of fuel injects at the precise point of the engine's cycle. The engine ECM also provides
the signal to the solenoid in the fuel injection pump. The solenoid controls a valve in the fuel injection pump, which
controls the pressure in the fuel manifold. Fuel not required for the engine diverts away from the fuel injection
pump back to the fuel tank.
The engine ECM adjusts injection timing and fuel pressure for the best engine performance, fuel economy, and
control of exhaust emissions.
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Programmable software inside the engine ECM sets certain limits on the amount of fuel injected into the cylinders.
The FRC Limit is a limit based on inlet manifold air pressure and engine rpm. The Fuel Ratio Control (FRC) Limit
controls the air/fuel ratio in order to control the exhaust emissions. When the engine ECM senses a higher inlet
manifold air pressure, it increases the FRC Limit. A higher inlet manifold air pressure indicates that there is more
air in the cylinder than fuel. When the engine ECM increases the FRC Limit, it allows more fuel into the cylinder.
The Rated Fuel Limit is a limit based on the power rating of the engine and on engine rpm. The Rated Fuel Limit
enables the engine power and torque outputs to conform to the power and torque curves of a specific engine
model. These limits are in the programmable software. However, they cannot be changed.
Cool Engine Elevated Idle Feature
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This feature temporarily elevates low idle speed when the engine is cold. The engine speed will increase to
approximately 1200 rpm when the feature is active. This feature becomes active when the machine is NOT
WORKING for approximately ten minutes. This feature is enabled unless any of the following occurs:
Parking brake is disengaged
Transmission is not in neutral
Throttle position has changed by 25% or more after feature is enabled
Coolant temperature is above 158F (70C) (lower limit) on initial power-up
The inlet manifold temperature isabove 41F (5C) on initial power-up
Coolant temperature is above 176F (80C)
Any of the following will also disable this feature:
Coolant temperature sensor failure
Inlet manifold temperature sensor failure
Throttle position switch failure
Transmission gear input failure
A false reading over the data link for the parking brake set or neutral set
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