The electronic system consists of the following components: the ECM, the mechanically actuated electronically controlled unit injectors (MEUI), the wiring harness, the switches and the sensors. The ECM is the computer. The personality module is the software for the computer. The personality module contains the operating maps. The operating maps define the following characteristics of the engine:
- Horsepower
- Torque curves
The ECM determines the timing and the amount of fuel that is delivered to the cylinders. These decisions are based on the actual conditions and/or on the desired conditions at any given time.
The ECM compares the desired engine speed to the actual engine speed. The actual engine speed is determined through the engine speed/timing sensor. The desired engine speed is determined through the following items:
- Throttle position sensor
- Other input signals from sensors
- Certain diagnostic codes
If the desired engine speed is greater than the actual engine speed, the ECM injects more fuel in order to increase the actual engine speed.
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 to the solenoid. This high voltage signal energizes the solenoid. 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 limits engine power during cold mode operation and the ECM modifies injection timing during cold mode operation. Cold mode operation provides the following benefits:
- Increased cold weather starting capability
- Reduced warm-up time
- Reduced white smoke
Cold mode is activated whenever the engine temperature falls below a predetermined value. Cold mode remains active until the engine temperature rises above a predetermined value or until a time limit is exceeded.
The personality module inside the ECM sets certain limits on the amount of fuel that can be injected. The "FRC Fuel Limit" is used to control the air/fuel ratio for control of emissions. The "FRC Fuel Limit" is a limit that is based on the turbocharger outlet pressure. A higher turbocharger outlet pressure indicates that there is more air in the cylinder. When the ECM senses a higher turbocharger outlet pressure, the ECM increases the "FRC Fuel Limit". When the ECM increases the "FRC Fuel Limit", the ECM allows more fuel into the cylinder. The "FRC Fuel Limit" is programmed into the personality module at the factory. The "FRC Fuel Limit" cannot be changed.
The "Rated Fuel Limit" is a limit that is based on the power rating of the engine and on engine rpm. The "Rated Fuel Limit" is similar to the rack stops and to 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 for a specific engine rating. The "Rated Fuel Limit" is programmed into the personality module at the factory. The "Rated Fuel Limit" cannot be changed.
Once the ECM determines the amount of fuel that is required, the ECM must determine the timing of the fuel injection. The ECM determines the TOP CENTER position of each cylinder from the engine speed/timing sensor's signal. The ECM decides when fuel injection should occur relative to the top center position and the ECM provides the signal to the injector at the desired time. The ECM adjusts timing for optimum engine performance, for optimum fuel economy, and for optimum control of white smoke.
Certain parameters that affect the engine operation may be changed with the Caterpillar Electronic Technician (ET). The parameters are stored in the ECM, and some parameters are protected from unauthorized changes by passwords. These passwords are called factory passwords.
Several system configuration parameters and most logged events are protected by factory passwords. Factory passwords are available only to Caterpillar dealers. Refer to Troubleshooting, "Factory Passwords" for additional information.