BOSCH MOTRONIC 4.1 ENGINE MANAGEMENT SYSTEM OVERVIEW

 BOSCH MOTRONIC 4.1 ENGINE MANAGEMENT SYSTEM OVERVIEW

Motronic 4.1 operation

The electronic system used to control the GM 8 valve engines (1987 to 1990) is labelled Motronic 4.1 and is a fully integrated EMS that controls primary ignition, fuelling and idle control from within the same ECU. In addition the ignition point and injection duration are jointly processed by the ECU 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 35 pin connector and multi-plug connects the ECU to the battery, sensors and actuators.

Basic ECU operation

A permanent voltage supply is made from the vehicle battery to pin 18 of the ECU. This allows the self-diagnostic function to retain data of an intermittent nature. Once the ignition is switched on, a voltage supply to the ignition coil and to ECU pin 35 is made from terminal 87 of the main fuel injection relay.

The majority of sensors (other than those that generate a voltage such the CAS and OS), are now provided with a 5.0 volt reference supply from a relevant pin on the ECU. When the engine is cranked or run, a speed signal from the CAS causes the ECU to earth pin 20 so that the fuel pump will run. Ignition and injection functions are also activated. All actuators (Injectors, ISCV, FTVV etc), are supplied with nbv from the main relay and the ECU completes the circuit by pulsing the relevant actuator wire to earth.