BOLT 2H0886 - Caterpillar

System Operation
The 3512 Industrial Engine is an electronically controlled engine equipped with an Electronic Control Module (ECM) to control fuel rate instead of using flyweights and linkages found in mechanically governed engines. The electronic control system also replaces the mechanical fuel ratio control (FRC), the torque control group, and various adjustment screws.The ECM uses several sensor input signals to calculate desired rack position and varies the voltage to the Mechanical Unit Injection (MUI) Interface Module. The MUI Interface Module drives the Rack Actuator which is connected to the rack by an external linkage. The Rack Position Sensor indicates when desired rack position is reached.Electronic Controls
The electronic control system consists of three main components: the ECM, the Personality Module, and the MUI Interface Module. The ECM is the computer hardware which controls the engine and the Personality module is the software which controls how the computer behaves. The MUI Interface Module provides signal conditioning that allows the ECM to position the rack actuator.Rack Controls
The ECM determines the desired engine rpm based on throttle inputs and load. The ECM attempts to maintain the desired engine rpm by sensing actual engine rpm with the Engine Speed Sensor and controlling the rack.To move the rack, the ECM adjusts the signal voltage to the MUI Interface Module, which adjusts current to the Rack Actuator to increase or decrease rack. The ECM increases or decreases the signal voltage to the MUI Interface Module until the Rack Position Sensor indicates that the desired rack position has been reached.The ECM sets certain limits on the amount of fuel that can be injected. FRC Rack is a rack limit used to reduce smoke during acceleration and operates in a manner similar to the FARC on a mechanically governed engine. When the ECM senses a higher inlet manifold (Boost) pressure (more available air for combustion), the FRC Rack limit is increased to allow more fuel. Rated Rack is a limit based on the power rating of the engine. It is similar to the rack stops and the torque spring on a mechanically governed engine. Rated Rack determines maximum power and torque values for a specific engine family and rating. FRC Rack and Rated Rack are programmed by the factory into the Personality Module.
Figure 1.1 - Electronic Governor Block DiagramProgrammable Parameters
Certain parameters that effect engine operation may be changed with an electronic service tool. These parameters are stored in the ECM and are either System Configuration Parameters or Customer Parameters. System Configuration Parameters are parameters that affect power ratings or emissions. Customer Parameters affect settings such as low and high idle rpm.Passwords
System Configuration Parameters are protected from unauthorized changes by Factory Passwords. Customer Parameters are protected by Customer Passwords that are programmed by the customer.Self-Diagnostics
The ECM has some ability to diagnose itself. When a problem is detected, a diagnostic code is generated and the diagnostic code is indicated on the Diagnostic Lamp as a series of flashes. In most cases, the diagnostic code is also stored