DISC-FRICTION 1938638 - Caterpillar

System Operation
Engine Governor
The ECM governs the engine. The ECM determines the timing, the injection pressure, and the amount of fuel that is delivered to each cylinder. These factors are based on the actual conditions and on the desired conditions at any given time during starting and operation.The ECM uses the throttle position sensor to determine the desired engine speed. The ECM compares the desired engine speed to the actual engine speed. The actual engine speed is determined through interpretation of the signals that are received by the ECM from the engine speed/timing sensors. If the desired engine speed is greater than the actual engine speed, the ECM requests that more fuel is injected in order to increase engine speed.Timing Considerations
Once the ECM has determined the amount of fuel that is required, the ECM must determine the timing of the fuel injection. Fuel injection timing is determined by the ECM after processing input from the following components:
Coolant temperature sensor
Intake manifold temperature sensor
Intake manifold pressure sensor
Atmospheric pressure sensorThe ECM adjusts timing for optimum engine performance and for the fuel economy. Actual timing and desired timing cannot be viewed with Caterpillar Electronic Technician (ET). The ECM determines the location of top center of the number one cylinder from the signals that are provided by the engine speed/timing sensors. The ECM determines when injection should occur relative to the top center. The ECM then provides the signal to the injector at the desired time.Fuel Injection
The ECM sends high voltage signals to the injector solenoids in order to energize the solenoids. By controlling the timing and the duration of the high voltage signals, the ECM can control the following aspects of injection:
Injection timing
Fuel deliveryThe flash file inside the ECM establishes certain limits on the amount of fuel that can be injected. The "FRC Fuel Limit" is a limit that is based on the intake manifold pressure. The "FRC Fuel Limit" is used to control the air/fuel ratio for control of emissions. When the ECM senses a higher intake manifold pressure, the ECM increases the "FRC Fuel Limit". A higher intake manifold pressure indicates that there is more air in the cylinder. When the ECM increases the "FRC Fuel Limit", the ECM changes the control signal to the injector. The signal will allow more fuel into the cylinder.The "Rated Fuel Limit" is a limit that is based on the power rating of the engine and on the engine rpm. The "Rated Fuel Limit" is like the rack stops and the torque spring on a mechanically governed engine. The "Rated Fuel Limit" provides the power curves and the torque curves for a specific engine family and a specific engine rating. All of these limits are determined at the factory. These limits cannot be changed. Other ECM Functions for Performance
The ECM may also provide enhanced control of the engine for functions such as retarding the engine and controlling the cooling fan. Refer to Troubleshooting, "Configuration Parameters" for supplemental information about the systems that can be monitored