BASE 0902898 - Caterpillar

Introduction
An Electronic Control Module (ECM) controls most of the functions of the engine. The ECM is an electronic engine control that is mounted on the side of the engine. The ECM monitors inputs from various sensors in order to activate relays, solenoids, actuators, etc at the appropriate levels. The ECM supports the following four functions:
Start/stop sequencing
Ignition control
Engine speed governing
Engine monitoring and protectionThe following functions are optional:
Air/fuel ratio control
Prelubrication and post lubricationStart/Stop Sequencing
The ECM contains the logic and the outputs for control of engine starting and of engine shutdown. The logic can be programmed by the customer. The logic responds to signals from the following components:
Engine control switch
Emergency stop switch
Remote start switch
Data link
Prelubrication system
Other inputsWhen the programmable logic determines that it is necessary to crank the engine, the ECM supplies +Battery voltage to the relay for the starting motor. The ECM removes the voltage when the programmable crank terminate speed is reached or when a programmable cycle crank time has expired.The engine must be equipped with an energize-to-run Gas Shutoff Valve (GSOV). The source of the voltage to the GSOV depends on the engine's configuration. The GSOV may be energized by the customer's equipment or by the engine's control system.If the engine's control system controls the GSOV, the ECM supplies +Battery voltage to the GSOV whenever the programmable logic determines that fuel is required to operate the engine.For more information on programmable parameters, see Troubleshooting, "Programming Parameters".Ignition Control
The ECM provides variable ignition timing that is sensitive to detonation.Each cylinder has an ignition transformer that is located under the valve cover for the cylinder. To initiate combustion, the ECM sends a pulse of approximately 100 volts to the primary coil of each ignition transformer at the appropriate time and for the appropriate duration. The transformers step up the voltage in order to create a spark across the spark plug electrode.Detonation sensors monitor the engine for excessive detonation. The engine has two detonation sensors. Each sensor monitors a cylinder bank. The sensors generate data on vibration that is processed by the ECM in order to determine detonation levels. If detonation reaches an unacceptable level, the ECM retards the ignition timing of the engine. If retarding the timing does not limit detonation to an acceptable level, the ECM shuts down the engine.The ECM provides extensive diagnostics for the ignition system. The ECM also contains an input for ignition timing in order to allow operation with alternate fuels such as propane that require a timing offset.Engine Speed Governing
The ECM maintains the desired engine speed by controlling the electronic actuator for the throttle. The actuator is located above the air inlet manifold.The actuator is electrically controlled and electrically actuated. The ECM sends a throttle command to the actuator via the CAN data link. The actual throttle position can be determined by comparing a scribe mark on the throttle shaft with the increments on a protractor.Desired engine speed is determined by the status of the idle/rated switch, the desired speed input (analog voltage or 4