HARNESS AS 8V5282 - Caterpillar

System Operation
Engine Governor
The ECM governs the engine. The ECM determines the timing, the injection pressure, and the amount of fuel that is delivered to each cylinder. These factors are based on the actual conditions and on the desired conditions at any given time during starting and operation.For variable speed engines, the ECM uses the throttle position sensor to determine the desired engine speed. The ECM compares the desired engine speed to the actual engine speed. The actual engine speed is determined through interpretation of the signals that are received by the ECM from the engine speed/timing sensors. If the desired engine speed is greater than the actual engine speed, the ECM allows more fuel to be injected, increasing engine speed.Timing Considerations
Once the ECM has determined the amount of fuel that is required, the ECM must determine the timing of the fuel injection. The ECM adjusts timing for optimum engine performance and for the fuel economy. Actual timing and desired timing cannot be viewed with the electronic service tool. The ECM determines the location of top center of the number one cylinder from the signals that are provided by the engine speed/timing sensors. The ECM determines when injection should occur relative to the top center position. The ECM then provides the signal to the injector at the correct time.Fuel Injection
The common rail fuel system is controlled by the ECM. The ECM gathers data from several sensors on the engine. The ECM then uses this data to adjust the quantity of fuel being delivered as well as the timing of the injection event. The injection event begins when the ECM sends a signal to the injector solenoid to actuate the valve inside the injector. As the valve opens, the fuel flows from the fuel rail, through the fuel line, and into the injector. As the valve opening pressure is reached, the valve is lifted and the fuel is delivered at high pressure into the combustion chamber.The flash file inside the ECM establishes certain limits on the amount of fuel that can be injected. The "FRC Fuel Limit" is a limit that is based on the intake manifold pressure. The "FRC Fuel Limit" is used to control the air/fuel ratio for control of emissions. When the ECM senses a higher intake manifold pressure, the ECM increases the "FRC Fuel Limit". A higher intake manifold pressure indicates that there is more air in the cylinder. When the ECM increases the "FRC Fuel Limit", the ECM changes the control signal to the injector. The signal will allow more fuel into the cylinder.The "Rated Fuel Limit" is a limit that is based on the power rating of the engine and on the engine rpm. The "Rated Fuel Limit" is like the rack stops and the torque spring on a mechanically governed engine. The "Rated Fuel Limit" provides the power curves and the torque curves for a specific engine family and a specific engine rating. All of these limits are determined at the factory. These