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Electronic Control System
The ECM consists of two main components:
Control computer (hardware)
Personality module (software)
Illustration 1 g00648808
Personality moduleThe control computer is the microprocessor and the electronic circuitry. The personality module contains the software for the control computer. The software contains operating maps that define the following characteristics of the engine:
Horsepower
Torque curves
Engine speedEngine Governor
Illustration 2 g00686474
Diagram of the electronic governorThe ECM governs the engine speed by controlling the amount of fuel that is delivered by the injectors. Refer to Illustration 2. The desired engine speed is determined by input from the throttle switch. Actual engine speed is measured by the engine speed/timing sensors. The ECM changes the amount of fuel that is injected until the actual engine speed matches the desired engine speed.Fuel Injection
Illustration 3 g00648838
Block diagram for the fuel systemThe ECM controls the timing, the duration, and the pressure of the fuel that is injected. The ECM controls the timing and the duration by varying the signals to the injectors. The injectors will inject fuel only if the injector solenoid is energized by a 105 volt signal from the ECM. By controlling the timing and the duration of the 105 volt signal, the ECM can control the timing of the injection and the ECM can control the amount of fuel that is injected. The ECM modulates the injection pressure by varying the signal to the Injection Actuation Pressure Control Valve (IAPCV). The IAPCV controls the pressure of the high pressure oil. The high pressure oil pressurizes the fuel that is in the injectors. By controlling the signal to the IAPCV, the ECM controls the pressure of the fuel that is injected into the engine.The ECM limits engine power and the ECM modifies injection pressure and injection timing during Cold Mode operation. Cold Mode operation has the following benefits: increased startability, reduced warm up period and reduced white smoke. Cold Mode is active if the engine oil temperature falls below a predetermined value and other conditions are met. Cold Mode remains active until the engine has warmed or until a time limit has been exceeded.The personality module inside the ECM sets certain limits on the amount of fuel that can be injected. The FRC Limit is a limit that is based on the boost pressure. The boost pressure is calculated as the difference in pressure between atmospheric pressure and turbocharger outlet pressure. The FRC 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 Limit. A higher boost pressure indicates that there is more air in the cylinder. When the ECM increases the FRC Limit, the ECM allows more fuel into the cylinder.The Rated Fuel Position is a limit that is based on the power rating of the engine. The Rated Fuel Position is similar to the rack stops and the torque spring on a mechanically governed engine. The Rated Fuel Position determines maximum power and torque values for a specific engine family and a specific rating. The Rated Fuel Position is programmed in the personality module at the factory.Programmable Parameters
System configuration parameters are parameters that are stored in the ECM. The stored parameters affect engine operation. The parameters are set at the factory. The parameters may be changed by using an electronic service tool. However, a factory password may be required to change certain parameters.Passwords
Several parameters and most logged events are protected by factory passwords. Factory passwords are available only to Caterpillar dealers.Note: Refer to Troubleshooting, "Factory Passwords" for information, if factory passwords are needed.