855952T 3 Mercury REED BLOCK ASSEMBLY

Illustration 1 g03340475This engine was designed for electronic control. Each cylinder has an electronic unit injector. A solenoid on each injector controls the amount of fuel that is delivered by the injector. The Electronic Control Module (ECM) sends a signal to each injector solenoid in order to provide complete control over the operation of the fuel injection system.Standard Diesel Injection
Electronic Controls
The electronic system consists of the following components: the ECM, the mechanically actuated electronically controlled unit injectors (MEUI), the wiring harness, the switches and the sensors. The ECM is the 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 delivered to the cylinders. These decisions are based on the actual conditions and/or 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 a signal from the engine speed/timing sensor. The desired engine speed is determined through the following items:
Throttle position sensor
Other input signals from sensors
Certain diagnostic codesIf 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.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 signal of the engine speed/timing sensor. The ECM determines 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 optimum engine performance, for optimum fuel economy, and for optimum control of white smoke.Programmable Parameters
Certain parameters that affect the engine operation may be changed with the Caterpillar Electronic Technician (ET). The parameters are stored in the ECM, and some parameters are protected from unauthorized changes by 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.Dynamic Gas Blending (DGB)
The DGB engine kit automatically adjusts to changes in incoming gas fuel quality and pressure allowing diesel engines to run on a wide variety of fuels. The kit has an engine electrical and protection system that protects the engine from excessive heat and detonation during the combustion process. In order to maintain detonation protection and engine life, it is necessary to regulate the flow of gaseous fuel. Through continuous engine monitoring, the DGB engine kit achieves maximum substitution of gaseous fuel while maintaining engine life.The key components of the DGB engine electrical and protection systems are:
A4 Engine electronic control module
Integrated sensor module
Detonation sensors
Exhaust temperature sensorsEngine Control Module (ECM)
All engine functions are controlled by an integrated A4:E4 ECM. The ECM monitors the status of the various systems and displays the system operating values. The ECM uses these same values to generate alarms and shutdowns to protect the engine.The ECM provides the basic principles for:
Start/stop sequencing
Engine speed governing
Gas fuel valve actuation
Monitoring and protection
Diagnostic codesIntegrated Sensor Module (ISM)
In addition to the A4:E4 ECM the engine employs an A3 Integrated ISM. The ISM has responsibility for monitoring the engine detonation sensors, the individual cylinder exhaust temperature, and the engine driven load percentage.The ISM receives inputs from the following components:
CAN local data link
CAN global data link
Cylinder temperature thermocouples
Detonation sensors
Cam position sensor #1The ISM receives these inputs and communicates the inputs to the ECM.The maximum gas substitution value is determined by a combination of factory mapping and dynamically monitored parameters. The control system actively monitors the following inputs to determine the maximum gas substitution allowed at a driven load:
The detonation sensor input
The engine exhaust temperature input
Fuel actuator valve positionThe control system and factory mapping utilize differing strategies during startup and at various operating loads.