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Electronic Controls
Electronic Control Module
The ECM consists of two main components, the control computer (hardware) and the personality module (software). The control computer consists of a microprocessor and electronic circuitry. The personality module is the software for the control computer which stores operating maps that define power and torque curves refer to illustration 1. The two works together in order to control engine operation.
Illustration 1 g00648808
Personality module
Engine Governor
Illustration 2 g01899814
Diagram of the electronic governor
The 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 detected 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 system
The ECM controls the timing and the amount of fuel that is delivered to the cylinders. This determination is based on the actual conditions and 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 via a signal from the engine speed/timing sensor. 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 amount of fuel that is injected.Fuel Ratio Control (FRC)
The personality module inside the ECM sets certain limits on the amount of fuel that can be injected. The fuel ratio control 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.Rated Fuel Position
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.Cold Mode Operation
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 smokeCold 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.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 calculates the fuel injection timing relative to the top center position of the individual pistons. The ECM also provides the signal to the injector at the desired time. The ECM adjusts timing for optimum engine performance, optimum fuel economy, and optimum control of white smoke.Injection Actuation Pressure Control System
The injection actuation pressure control valve (IAPCV) that is internal to the unit injector hydraulic pump is a precision displacement control actuator. This actuator controls the swashplate angle for the variable displacement unit injector hydraulic pump. The swashplate angle controls the pump output flow to the injectors. The injection actuation pressure sensor provides a sensor signal to the ECM. The sensor signal represents the output pressure of the unit injector hydraulic pump. A desired pressure is calculated by the ECM and a control signal is sent to the IAPCV.Self-Diagnostics
The ECM has the ability to detect problems with the electronic system and with engine operation. When a problem is detected, a code is generated. An alarm may also be generated. There are two types of codes:
Diagnostic
EventDiagnostic Code - When a problem with the electronic system is detected, the ECM generates a diagnostic code. This indicates the specific problem with the circuitry.Diagnostic codes can have two different states:
Active
LoggedActive Code - An active diagnostic code indicates that an active problem has been detected. Active codes require immediate attention. Always service active codes prior to servicing logged codes.Logged Code - Every generated code is stored in the permanent memory of the ECM. The codes are logged.Event Code - An event code is generated by the detection of an abnormal engine operating condition. For example, an event code will be generated if the oil pressure is too low. In this case, the event code indicates the symptom of a problem.Logged codes may not indicate that a repair is needed. The problem may have been temporary. The problem may have been resolved since the logging of the code. If the system is powered, it is possible to generate an active diagnostic code whenever a component is disconnected. When the component is reconnected, the code is no longer active. Logged codes may be useful to help troubleshoot intermittent problems. Logged codes can also be used to review the performance of the engine and of the electronic system.Password
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.