NUT 2K8851 - Caterpillar

Note: This section contains some general information about the engine electronic system and sensors. For additional information, refer to Systems Operation/Testing and Adjusting, UENR0514 or Troubleshooting, UENR0515.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
Precise control of engine operation
Protection from detonation
Timing control of individual cylinders
Knock sensors
Illustration 1 g06243501
(1) Junction boxMost of the functions of the electronic system are provided by the Engine Control Module (ECM). The ECM is a sealed unit that is located inside a junction box (1) at the rear of the engine.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 and protection of the engineGoverning of the Engine RPM
The ECM receives a signal from the speed/timing sensor. The ECM maintains the desired engine rpm through electrical control of the engine throttle.Control of Ignition
Each cylinder has an ignition transformer that is located under the top of each valve cover. To initiate combustion in each cylinder, the ECM sends a pulse to the primary coil of the ignition transformer at the correct time. The time is based on firing order and engine speed. 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.Control of Air/Fuel Ratio
The ECM determines the desired volumetric flow rate for fuel. The determination is based on the components: actual engine speed, actual load, MAP, MAT, and internal maps. Next, the ECM sends information on the desired fuel flow to the fuel metering valve via the CAN data link. The ECM adjusts the signal to the fuel metering valve to maintain emissions. The process is repeated continuously during engine operation.Start/Stop Control
The ECM contains the logic and the inputs for controlling the starting and stopping of the engine. The logic for starting and stopping can be programmed by the customer. The ECM supplies positive "+" battery voltage to the starting motor relay and the gas shutoff valve.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. The gas shutoff valve may be controlled by the customer.Monitoring Engine Operation
Sensors are used to monitor engine operation. Wiring harnesses connect the sensors to the ECM. The ECM uses the information from the sensors to monitor the engine. The ECM also uses the information from the sensors to control the engine. The information is also used to generate event codes, and diagnostic codes. The codes can be read with a Cat Electronic Technician (ET).Event - An event is a result of abnormal engine operation. If abnormal engine operation is detected, the ECM generates an event code.