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Bosch Motronic ECU

The Bosch digital Motronic ECU replaced the older analogue L-Jetronic system, to provide more precise control of the engine's fuelling and ignition timing which improves power, fuel economy and emissions.

Motronic is the trade name given to a range of digital engine management systems developed by Bosch.


Motronic 1.0 was one of the first digital engine-management systems developed by Bosch. The basic idea behind the system was to fully integrate and regulate all major engine system parameters, thereby enabling fuel delivery and spark timing control functions to be controlled by the same unit, in an attempt to achieve optimum efficiency, driveability and power output potential. These early Motronic systems integrated the spark timing element with then-existing Jetronic fuel injection technology.

Motronic 1.1 came next. First fitted to 6 cylinder models in 1987, it jointly processed the ignition point and injection duration so that the best moment for ignition and fuelling are determined for every operating condition. The injection function of the Motronic system is based on the well tried 'L' Jetronic system, although a number of refinements have improved operation. A 55 pin connector and multi-plug connects the ECU to the Battery, sensors and actuators.

Motronic 1.3 superseded 1.1 in 1988, and became the standard engine management system for all E30 models (with the exception of the 318iS). While similar to Motronic 1.1 in operation, the 1.3 has increased diagnostic capabilities, and can store many more detailed fault codes than 1.1. It also has a permanent 12-volt feed from the vehicle's battery which allows it to log intermittent faults in memory across several trips.


The electronic control unit (ECU) 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.

Fuel delivery, Ignition timing, and dwell angle are incorporated into the same ECU to create a 3-dimensional map of the engine parameters relating to engine speed and load, stored on a chip.

Crank position and engine speed is determined by a pair of sensors reading from the flywheel (or toothed pulley at the front of the engine on later models). A separate constant idle speed system monitors and regulates base idle speed settings.

On early systems, a 5th injector is used to provide extra fuel enrichment during different cold-start conditions.

Depending on application and version, an oxygen sensor may be fitted (the system was originally designed for leaded fuel).

Once the ECU has received all the correct signals from its sensors, it will fire the injectors. The ECUs 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.

ECU Codes

ECU Number System Models From/To
0261 200 174 Motronic 316i 1988 Onwards
0261 200 989 Motronic 316i
0261 200 157 Motronic 318i 1987 - 88
0261 200 175 Motronic 318i
0261 200 386 Motronic 318i
0261 200 387 Motronic 318i
0261 200 175 Motronic 318iS 1989 onwards
0261 200 172 Motronic 320i and 325i 1987
0261 200 381 Motronic 320i 1987 onwards
0261 200 164 Motronic 325i Auto 9/87 onwards
0261 200 073 Motronic 325i Chrome bumper 1985 - 87
0261 200 173 Motronic 320i and 325i Plastic bumper 9/87 onwards
0261 200 380 Motronic 325i 8/88 onwards
0261 200 071 Motronic Early 195/200bhp M3 and Evo 1
0261 200 090 Motronic M3 Evo II
0261 200 091 Motronic M3 with 215bhp
0261 200 092 Motronic M3 Sport Evo
0261 200 042 Motronic 325e until 9/85
0261 200 087 Motronic 320iS
0261 200 074 Motronic 325e 9/85 onwards (Low compression)


Converting to Motronic 1.3

Main article: Converting to Motronic 1.3

The last generation of the Motronic system, as fitted to all E30 models (excluding the 318iS). While Motronic 1.3 won't improve the performance of your engine much, it will give you greater access to spare parts to keep your car running, and fewer issues to fix in the future compared to the problematic and troublesome Jetronic systems.


The Motronic system can be 'chipped', which involves replacing the standard EPROM (Erasable Programmable Read Only Memory) chip with one containing a performance enhancing program or 'map' for improved driveability, throttle response, mpg, raised rev limit, etc. The flat spots are eliminated by removing the unnecessary parts in the standard program that are there to cater for low-grade fuels, high altitudes, etc. used in other parts of the world.

Chips can be found all over the internet, promising dramatic power increases, huge fuel savings and all sorts of other fantasies. While some chips can offer a noticeable improvement in either power or economy, chipping your car won't yield massive improvements. However, good chips can be found; check out our list of recommended chips.

Learn more about fitting a chip.


The existing EPROM can be blanked in an ultra-violet EPROM eraser and a new program burned into it using an EPROM programmer linked to a PC. This is referred to as a remap, commonly carried out while dyno testing for optimising the fuelling, etc.

Learn more about remapping Motronic.

Compiled by Speedtouch and Kedge.

Third Party Engine Management

When you feel you've reached the limit of what Motronic can do for you, it's time to start thinking about standalone engine management. Learn more about upgrading your engine management.