Motronic is the trade name given to a range of digital engine control units developed by Robert Bosch GmbH (commonly known as Bosch). The unique feature of these systems, compared with their predecessors, is combined control of fuel and spark in a single unit. By controlling fuel and spark together, many aspects of the engine's characteristics (such as power, fuel efficiency, driveability and emissions) can be improved.
Often known as "Motronic basic", Motronic ML1.x was one of the first digital engine-management systems developed by Bosch. These early Motronic systems integrated the spark timing element with then-existing Jetronic fuel injection technology. It was originally developed and first used in the BMW 7-Series, before being implemented on several Volvo and Porsche engines throughout the 1980s.
The components of the Motronic ML1.x systems for the most part remained unchanged during production, although there are some differences in certain situations. The engine control module (ECM) receives information regarding engine speed, crankshaft angle, coolant temperature and throttle position. An air flow meter also measures the volume of air entering the induction system.
If the engine is naturally aspirated, an air temperature sensor is located in the air flow meter to work out the air mass. However, if the engine is turbocharged, an additional charge air temperature sensor is used to monitor the temperature of the inducted air after it has passed through the turbocharger and intercooler, in order to accurately and dynamically calculate the overall air mass.
- Main system characteristics
- Fuel delivery, ignition timing, and dwell angle incorporated into the same control unit.
- Crank position and engine speed is determined by a pair of sensors reading from the flywheel.
- Separate constant idle speed system monitors and regulates base idle speed settings.
- 5th injector is used to provide extra fuel enrichment during different cold-start conditions. (in some configurations)
- Depending on application and version, an oxygen sensor may be fitted (the system was originally designed for leaded fuel).
The Motronic 1.1 System was used by BMW from 1987 on motors such as the M20.
The systems have the option for a lambda sensor, enabling their use with catalytic converter-equipped vehicles. This feedback system allows the system analyse exhaust emissions so that fuel and spark can be continually optimised to minimise emissions. Also present is adaptive circuitry, which adjusts for changes in an engine's characteristics over time. Some PSA engines also include a knock sensor for ignition timing adjustment, perhaps this was achieved using an external Knock Control Regulator.
The Motronic units have 2 injection outputs, and the injectors are arranged in 2 "banks" which fire once every two engine revolutions. In an example 4-cylinder engine, one output controls the injectors for cylinders 1 and 3, and the other controls 2 and 4. The system uses a "cylinder ID" sensor mounted to the cam-shaft to detect which cylinders are approaching the top of their stroke, therefore which injector bank should be fired. During start-up (below 600 RPM), or if there is no signal from the cylinder ID sensor, all injectors are fired simultaneously once per engine revolution. In BMW vehicles, this Motronic version did not have a cylinder ID and as a result, both banks of injectors fired at once.
The Motronic 1.1 and 1.3 systems are largely similar, the main improvement being the increased diagnostic capabilities of Motronic 1.3. The 1.3 ECM can store many more detailed fault codes than 1.1, and has a permanent 12-volt feed from the vehicle's battery which allows it to log intermittent faults in memory across several trips. Motronic 1.1 can only advise of a few currently-occurring faults.
This system was used on some of General Motors Family II engines.
The key feature of Motronic 1.7 is the elimination of an ignition distributor, where each cylinder has its own ignition coil (coil-on-plug). Motronic 1.7 family has versions 1.7, 1.7.2, 1.7.3, all of them used on M42/M43 engines in BMW 3 Series (E36) up to 1998 and BMW 5 Series (E34) up to 1995.
Motronic ML 2.1 Series
The ML 2.1 system integrates an advanced engine management with 2 knock sensors provision for adaptive fuel & timing adjustment, purge canister control, precision sequential fuel control & diagnostics (pre OBD-1). Fuel enrichment during cold-start is achieved by altering the timing of the main injectors based on engine temperature. The idle speed is also fully controlled by the digital Motronic unit, including fast-idle during warm-up. Updated variants ML 2.10.1 thru 2.5 add MAF Mass Air Flow sensor logic and direct fire ignition coils per cylinder. Motronic 2.1 is used in the Porsche 4 cyl 16V 944S/S2/968 and the 6 cyl Boxer Carrera 964 & 993, Opel/Vauxhall, FIAT & Alfa Romeo engines.
Motronic ML 3.1
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 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.