SCREW 1A2935 - Caterpillar

Introduction
The Electronic Control Module (ECM) controls most of the functions of the engine. The ECM is an environmentally sealed unit that is mounted in a terminal box on the engine. The ECM monitors various inputs from sensors in order to activate relays, solenoids, etc at the appropriate levels. The ECM supports the following five primary functions:
Engine speed governing
Ignition control
Air/fuel ratio control
Start/stop sequencing
Engine monitoring and protectionEngine Speed Governing
The ECM maintains the desired engine speed by controlling the actuator for the throttle. The actuator is located at the flange of the air inlet manifold.The actuator is electrically controlled and hydraulically actuated. A high pressure pump provides hydraulic pressure with oil from a system that is separate from the engine oil. The high pressure oil supply is monitored by a pressure switch that generates an event code if the pressure drops below an acceptable level. The throttle position is controlled in open loop mode: there is no feedback from the throttle position.The ECM issues a throttle command that represents a percent of the level of electrical current. The output can be viewed on the Caterpillar Electronic Technician (ET). The actual throttle position can be viewed on a mechanical pointer that is built into the mechanism of the throttle.Desired engine speed is determined by the status of the idle/rated switch, the desired speed input (analog voltage or 4 to 20 mA), and parameters such as maximum engine high idle speed that are programmed into the software. Actual engine speed is detected via a signal from the speed/timing sensor. Parameters such as governor gain can be programmed with Cat ET.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 G3516B Engine has eight detonation sensors. Each sensor monitors two adjacent cylinders. 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 affected cylinder or cylinders. 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 provides a switch for ignition timing in order to allow operation with alternate fuels such as propane that require a timing offset.Air/Fuel Ratio Control
The ECM provides control of the air/fuel mixture for performance and for efficiency at low emission levels. The system consists of an electronic fuel metering valve, output drivers in the ECM, and maps in the ECM. The engine may be equipped with a system that senses the amount of oxygen in the exhaust.