TAG - CAUTION 5M4328 - Caterpillar

System Operation
The engine consists of a fuel system that utilizes Hydraulic Electronic Unit Injectors (HEUI). A solenoid on each injector controls the amount of fuel that is delivered by the injector. An axial piston pump that is referred to as the unit injector hydraulic pump pressurizes oil in order to activate the injector. An Electronic Control Module (ECM) sends a signal to the injection actuation pressure control valve in order to control injection pressure. Electrical signals are sent to each injector solenoid in order to inject fuel into the cylinders.Electronic Controls
The electronic system for the engine consists of the ECM, the wiring harness, the engine sensors, the switches, the injection actuation pressure control valve, the unit injector hydraulic pump, the HEUI injectors and the interface for the particular application. The ECM is a computer. The flash file is the software for the computer. The flash file contains the operating maps. The operating maps define the following characteristics of the engine:
Horsepower
Torque curvesThe ECM determines the timing and the amount of fuel that is injected into the cylinders. The calculations are based on the actual conditions and the desired conditions at any given time.The ECM compares the desired engine speed to the actual engine speed in order to calculate an adjustment to the injection timing and to the duration. The actual engine speed is determined via a signal from the engine speed/timing sensor. If the desired engine speed is greater than the actual engine speed, the ECM increases the injection duration in order to increase the actual engine speed.Fuel Injection
The ECM controls the amount of fuel that is injected by varying the signals to the injectors. The ECM sends a high voltage signal to the solenoid. The injectors pump fuel only while the injector solenoid is energized. This high voltage signal energizes the solenoid. By controlling the timing and the duration of the high voltage signal, the ECM can control injection timing and the ECM can control the amount of fuel that is injected.The flash file inside the ECM sets certain limits on the amount of fuel that can be injected. The "FRC Fuel Limit" is used to control the air/fuel ratio for control of emissions. The "FRC Fuel Limit" is a limit that is based on the turbocharger outlet pressure. A higher turbocharger outlet pressure indicates that there is more air in the cylinder. When the ECM senses a higher turbocharger outlet pressure, the ECM increases the "FRC Fuel Limit". When the ECM increases the "FRC Fuel Limit", the ECM allows more fuel into the cylinder. The "FRC Fuel Limit" is programmed into the flash file at the factory. The "FRC Fuel Limit" cannot be changed.The "Rated Fuel Limit" is a limit that is based on the power rating of the engine and of the engine speed. The "Rated Fuel Limit" has a function that is similar to the rack stops and the torque spring on a mechanically governed engine. The "Rated Fuel Limit" provides the power curves and