BOLT 9F2773 - Caterpillar

Note: This section contains some general information about the engine electronic system and sensors. For more information, refer to Systems Operation/Testing and Adjusting.Electronic System
The Caterpillar 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
Protection from detonation
Timing control of individual cylinders
Illustration 1 g00527903
Junction boxMost of the functions of the electronic system are provided by the Electronic Control Module (ECM). The ECM is a sealed unit. The ECM 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 receives a signal from the speed/timing sensor. The ECM maintains the desired engine rpm through electrical control of the electrohydraulic actuator. The actuator regulates the throttle plate.The actual throttle position can be observed on a mechanical indicator that is on the housing of the actuator.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 determination is based on the desired engine speed, the actual engine speed, and the calculated load. Next, the ECM sends information on the desired flow of air and fuel to the fuel metering valve via a PWM signal. The ECM monitors the content of the resulting exhaust gas. The ECM fine tunes the signal to the fuel metering valve in order to achieve the desired exhaust oxygen. 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 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 in order 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 in order to monitor engine operation. Wiring harnesses connect the sensors to the ECM. The ECM uses information from the sensors in order to monitor the engine. The ECM also uses information from the sensors in order to control the engine. The information is also used to generate event codes, and diagnostic codes. The codes can be read