PISTON GP 3331461 - Caterpillar

Introduction
Two Electronic Control Modules (ECM) are used to control the engine. One module is the master ECM and the other module is the slave ECM. Each module is an environmentally sealed unit that is mounted in a terminal box on the engine.The master ECM controls most of the functions of the engine. The master ECM monitors various inputs from sensors in order to activate relays, solenoids, etc at the appropriate levels. The master ECM supports the following five primary functions:
Engine speed governing
Air/Fuel ratio control
Start/Stop sequencing
Engine monitoring and protection
Control of the ignition and detonation of the left cylinder bankThe slave ECM primarily supports the control of ignition and detonation of the right cylinder bank.Engine Speed Governing
The master 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 throttle 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 master 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.Air/Fuel Ratio Control
The master ECM provides control of the air/fuel mixture for performance and efficiency at low emission levels. The system consists of an electronic fuel metering valve, sensors, output drivers in the master ECM, and maps in the master ECM. The control compensates for changes in the BTU of the fuel in order to maintain desired emission levels.The ECM maintains the engine's exhaust emissions at the levels that are required at the site. The ECM may use charge density feedback or oxygen feedback in order to control emissions.Charge Density Feedback - The master ECM monitors the generator's power output, the temperature of the air in the inlet manifold, and the pressure of the air in the inlet manifold. The ECM uses the information in order to adjust the signal for the flow of air and of fuel. This process occurs whenever the engine load is above 25 percent.Oxygen Feedback - The ECM monitors the amount of oxygen in the exhaust gas via the oxygen sensor. The ECM adjusts the signal for the flow of air and of fuel. This process occurs whenever