HOUSING AS-DIFFERENTIAL 9D8972 - Caterpillar

The engine is designed for electronic control of most engine operating functions. The electronic system consists of an Electronic Control Module (ECM), the wiring harness, switches, sensors, and fuel injectors. The engine ECM receives information from the sensors and the switches on the engine. The engine ECM processes the information that is collected in order to control the engine. By altering the fuel delivery with the fuel injectors, the engine ECM controls the speed and the power that is produced by the engine. The Clean Emission Module (CEM)is controlled by the ECM. The system monitors the Diesel Particulate Filter (DPF).The following information provides a general description of the control system. Refer to the Systems Operation manual for detailed information about the control system.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