RENR5042-02 5 Troubleshooting Section Troubleshooting Section Fuel Injection The ECM controls the amount of fuel that is injected by varying the signals to the injectors. The injector 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. Electronic Troubleshooting i02286178 System Overview SMCS Code:
1900 System Operation The ECM limits engine power during cold mode operation and the ECM modifies injection timing during cold mode operation. Cold mode operation provides the following benefits: This engine is electronically controlled. Each cylinder has an electronic unit injector. The Electronic Control Module (ECM) sends a signal to each injector solenoid in order to control the operation of the fuel injection system. Increased cold weather starting capability Reduced warm-up time Electronic Controls Reduced white smoke 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: Cold mode is activated whenever the engine temperature falls below a predetermined value. Cold mode remains active until the engine temperature rises above a predetermined value or until a time limit is exceeded. 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 ECM at the factory. The “FRC Fuel Limit” cannot be changed. Horsepower Torque curves The 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 on 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. The desired engine speed is determined with the following factors: The “Rated Fuel Limit” is a limit that is based on the power rating of the engine and on engine rpm. The “Rated Fuel Limit” is similar to the rack stops and to 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 for a specific engine rating.
The “Rated Fuel Limit” is programmed into the ECM at the factory. The “Rated Fuel Limit” cannot be changed. Throttle signal Other input signals from sensors Certain diagnostic codes 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. Once the ECM determines the amount of fuel that is required, the ECM must determine the timing of the fuel injection. The ECM calculates 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 optimum engine performance, for optimum fuel economy, and for optimum control of white smoke.