Motronic 1.3

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All E30s have some kind of engine management system, this is controlled by the Engine Control Unit (ECU). Motronic is just a version of engine management produced by Bosch. and was used by many different car manufacturers. Its main function is to control the fuelling and timing of the engine. The last version of this system used in the E30 was Motronic 1.3.

If your engine is running an earlier management system, it is possible to convert it to Motronic 1.3.



Like all Motronic systems, Motronic 1.3 uses a variety of sensors dotted around the engine to take readings. Based on the data it receives, the engine can control fuelling and ignition timing. In the event of an error, the system will either prevent the car from starting to protect against damage, or will go into LOS or Limp-Home mode.

For a better understanding of how Motronic 1.3 achieves this, here's a breakdown of each function:

Basic ECU Operation

A permanent voltage supply is maintained from the battery to the ECU via pin #18 to allow the ECU to retain data. Upon switching on the ignition voltage is sent to ECU pin #27 and the ignition coil, causing ECU pin #36 to earth and consequentially actuating the main fuel injection relay.

Most sensors are provided a 5v reference supply from the corresponding ECU pin. When the engine is cranked/run a signal is sent from the CAS to ECU pin #3 which then runs the fuel pump. Ignition and injection functions are also activated. All actuators are supplied with nbv from the main relay and the ECU completes the circuit by pulsing the relevant actuator wire to earth.

Signal Processing

This bit is a tad complicated for my brain so I’m keeping it as simple as possible. Basic ignition timing is stored in a two dimensional map and the engine load and speed signals determines the ignition timing. The main engine load sensor is the AFS and engine speed is determined from the CAS signal. Correction factors are then applied for starting, idle, deceleration and part and full-load operation, the main correction factor being engine temperature.

Adaptive Function

The ECU is adaptive to changing engine operating characteristics and constantly monitors the data from the various sensors. As the engine or its components wear, the ECU reacts to new circumstances by adopting the changed values as a correction to the basic Map.

Self Diagnostic Function

M1.3 is able to carry-out self tests by examining signals from the engine sensors and then logs a code if it detects a fault. This code can then be read by plugging a reader into the Motronic Serial Port. This log is stored until the engine has been started more than 5 times since it was reported or it is manually wiped.

Service lights

There is a cluster of LED's on the dash: five green, one red and one Yellow. Up to five green LED's will light when the ignition is turned on. However, the LED's will extinguish once the engine is started. When the yellow light comes on, service is due. When the Red light comes on, this means that service is overdue by approximately 1000 miles. Once the service has been completed, the service lights should be reset.

Limited Operating Strategy (LOS)

If there is a serious fault with a sensor or it’s wiring M1.3 is able to substitute a fixed value in place of the sensor (AKA Limp Mode). The engine may still appear to run OK in LOS depending on which the failed sensor is. The substituted values are those of a hot engine so issues may only be noticed on cold start and the warm up period.

Reference voltage

Voltage supply from the ECU to many of the engine sensors is at a 5.0 volt reference level. This ensures a stable working voltage unaffected by variations in system voltage. The earth return connection for most engine sensors is made through an ECU pin that is not directly connected to earth. The ECU internally connects that pin to earth via one of the ECU pins that are directly connected to earth.