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Electronic System
The Cat Electronic System is a complete electronic control system for gas engines. The following benefits are the most significant advantages of the electronic system:
Air/Fuel ratio control
Extensive system diagnostics
Elimination of parts that are prone to mechanical wear
Precise control of engine operation
Engine protection
Timing control of individual cylinders
Illustration 1 g00527903
Junction box
Most of the functions of the electronic system are provided by the Electronic Control Module (ECM). The ECM is a sealed unit that is located inside a junction box.Five primary functions are supported by the ECM:
Governing of the engine rpm
Control of ignition
Control of the air/fuel ratio
Start/stop control
Monitoring of engine operationGoverning of the Engine RPM
The ECM maintains the desired engine speed through electrical control of the throttle. The throttle regulates the throttle plate.For more information on the desired speed input, see the Systems Operation/Testing and Adjusting manual.Control of Ignition
Each cylinder has an ignition transformer that is located under the valve cover. To initiate combustion in each cylinder, the ECM sends a pulse to the primary coil of the ignition transformer. The transformer increases the voltage which creates a spark across the spark plug electrode.The transformers are grounded through the valve cover. Use caution when a valve cover is removed.Always disconnect the ignition harness from the transformer when a valve cover is removed.An ignition harness connects each transformer to the ECM. The harness is routed inside the engine.Control of Air and Fuel
The ECM determines the desired volume for the flow rates of the air and fuel. The ECM sends information on the desired flow of air and fuel to the fuel metering valve. The ECM fine tunes the signal to the fuel metering valve to achieve the desired emissions. The process is repeated continuously during engine operation.Start/Stop Control
The ECM contains the logic and the outputs for controlling the starting and stopping of the engine. The logic for starting and stopping can be programmed by the customer.The engine uses an energize-to-run system. The gas shutoff valve must remain energized to supply fuel to the engine. If power is removed from the gas shutoff valve, the fuel is shut off.Monitoring Engine Operation
Sensors are used to monitor engine operation. Wiring harnesses connect the sensors to the ECM. The ECM uses information from the sensors to monitor the engine. The ECM also uses information from the sensors to control the engine. The information is also used to generate event codes, and diagnostic codes.Note: The codes can be read with Cat Electronic Technician (ET). The codes can also be read on the panel, if equipped.Event - An event is a result of abnormal engine operation. If abnormal engine operation is detected, the ECM generates an event code. The ECM can generate an alarm or a shutdown for abnormal engine operation. These conditions are some examples of events: high inlet air temperature, low oil pressure, and engine overspeed.Diagnostic - A diagnostic code is a result of a problem with the operating system or with the monitoring system. The ECM uses sensors and internal circuitry to monitor the system components. If a problem develops in a component or a wiring harness, the control system will sense the problem. The control system will notify the operator by creating a diagnostic code. Some examples of conditions that activate diagnostics are a short in a circuit for a sensor, an open circuit, or a noisy signal.Note: For detailed information on event codes and diagnostic codes, refer to the engine Troubleshooting manual.Sensors
Sensors provide information to the ECM. The information enables the ECM to control the engine as efficiently as possible over a wide range of operating conditions. The information is used for monitoring engine operation and for engine protection.Refer to the applicable Schematics manual for sensor locations and information on the sensors.