Motronic ML4.1
The Motronic 4.1 system was used on Opel / Vauxhall eight-valve engines from 1987–1990, and some PSA Peugeot Citroën XU9J-series engines.
Fuel enrichment during cold-start is achieved by altering the timing of the main injectors based on engine temperature, no "cold start" injector is required. The idle speed is also fully controlled by the Motronic unit, including fast-idle during warm-up (therefore no thermo-time switch is required).
The 4.1 system did not include provision for a knock sensor for timing adjustment. The ignition timing and fuel map could be altered to take account of fuels with different octane ratings by connecting a calibrated resistor (taking the form of an "octane coding plug" in the vehicle's wiring loom) to one of the ECU pins, the resistance depending on the octane adjustment required. With no resistor attached the system would default to 98 octane.
There is has a single output for the injectors, resulting in all injectors firing simultaneously. The injectors are opened once for every revolution of the engine, injecting half the required fuel each time.
Read more about this topic: Motronic