808005 Mercruiser SCREW, (.250-20 x .500)

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 a particular application. The ECM is the computer. The personality module is the software for the computer. The personality module 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 delivered to the cylinders. These decisions 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. The actual engine speed is determined through the engine speed/timing sensor. If the desired engine speed is greater than the actual engine speed, the ECM injects more fuel 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 injectors will pump fuel only if the injector solenoid is energized. The ECM sends a high voltage signal to the solenoid. 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 personality module (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 personality module (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 engine speed. The "Rated Fuel Limit" is similar to 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. The "Rated Fuel Limit" is programmed into the personality module (flash file) at the factory. The "Rated Fuel Limit" cannot be changed.Once the ECM determines the amount of fuel that is required, the ECM must determine the timing of the fuel injection. The ECM determines the top center position of each cylinder from the engine speed/timing sensor's signal. The ECM decides when fuel injection should occur relative to the top center position and the ECM provides the signal to the injector at the desired time. The ECM adjusts timing for the best engine performance, the best fuel economy, and the best control of white smoke.Injection Actuation Pressure Control System
The injection actuation pressure control valve (IAPCV) that is internal to the unit injector hydraulic pump is a precision displacement control actuator. This actuator changes the pump outlet flow that is based on the control current that is supplied by the ECM. The variable displacement unit injector hydraulic pump pressurizes only the amount of high pressure oil that is needed.Starting Aids
The following devices are used in order to improve the starting of the engine in cold weather conditions.
Air inlet heater
Oil grade plugsFor additional information on the Air Inlet Heater, refer to Troubleshooting, "Air Inlet Heater Circuit - Test".The oil grade plugs allow the ECM to use different starting strategies for cold weather conditions. These strategies are based on the oil grade that is used in the engine.Programmable Parameters
Certain parameters that affect the engine operation may be changed with electronic service tools. The parameters are stored in the ECM, and the parameters are protected from unauthorized changes by factory passwords.Passwords
Several system configuration parameters and most logged events are protected by factory passwords. Factory passwords are available only to Caterpillar dealers. Refer to Troubleshooting, "Factory Passwords" for additional information.