The controller performs the following main functions:
- fuel injection system control;
- ignition system control and ignition timing adjustment;
- cold engine start control;
- engine idle speed control;
- crankshaft speed control;
- regulation of oxygen content in exhaust gases (on vehicles with exhaust gas neutralizer);
- self-diagnosis.
When starting a cold engine, the controller generates ignition timing control pulses and fuel injection duration pulses for the injectors, the ignition advance angle is determined based on the crankshaft speed and coolant temperature. The maximum ignition advance angle is entered at a coolant temperature of -30°C. Fuel injection duration is determined depending on the intake air temperature, coolant temperature, battery voltage and engine speed. When starting a cold engine, each ignition pulse corresponds to an injection duration pulse, i.e. fuel is injected four times per working stroke.
The crankshaft speed at idle is maintained constant by the controller commands.
The ignition advance angle values stored in the controller's memory are compared with the actual values and adjusted accordingly, which eliminates changes in the engine's idle speed due to mechanical wear of parts, leaks, or differences in friction resistance between engines.
During acceleration, the controller ensures enrichment of the combustible mixture as follows. If the signal from the air flow meter potentiometer exceeds the values stored in the controller's memory during acceleration, the controller increases the fuel injection time in such a way as to bring the engine to the required load mode as quickly as possible. As the crankshaft speed approaches the required one, the injection duration and, consequently, the amount of fuel injected by the injectors gradually decreases.
If the controller receives a signal from the idle contact of the throttle switch, and the engine crankshaft speed exceeds 1080 rpm, the fuel supply is stopped. At the same time, the engine speed drops, and the intensity of this process depends on the operating conditions of the car. Before entering the idle mode, the controller checks the operation of the system when the fuel supply is stopped.
When the crankshaft speed reaches a certain value, the fuel supply is gradually resumed. In this case, the normal idle mode is set by the controller commands at a lower level than it was when the fuel supply was stopped. This helps to avoid interruptions in engine operation. The controller calculates the moments of stopping and resuming the fuel supply based on information from the coolant temperature sensor. In addition, the controller memory contains a special program for stopping the fuel supply at low engine load. This program begins to be executed only if the corresponding input parameter is received by the controller for some time, provided that the ignition advance angle is adapted to the new engine operating conditions.
The self-diagnostic system detects malfunctions of the controller and system components "Motronic ML4.1" and enters them into the controller's memory.
In case of a malfunction of the coolant temperature sensor, intake air temperature sensor, air flow meter potentiometer, the controller starts working according to the values accepted by default (default is the program selection of the variable value in the absence of an externally specified one). After the controller returns to normal mode, the use of the values accepted by default ceases. To facilitate troubleshooting, it is possible to request current parameters from the controller's memory and activate one or another element of the system by connecting a special device to the diagnostic connector.
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