General information Two types of Motronic engine management systems have been fitted to the Citroën BX 16valve. To provide fine control of the engine to suit prevailing operating conditions, the system controls the functions of both the fuel injection and ignition systems. The Electronic Control Unit (ECU) receives signals from various sensors and computes the optimum volume of fuel to be injected and the optimum ignition advance setting to suit the prevailing conditions. In the event of the failure of a system component, the ECU has the capability to permit the engine to operate, albeit at reduced power and efficiency, until the fault can be investigated. The following sensors supply the ECU with information: a) Airflow meter - measures the volume of air entering the engine b) Air temperature sensor - measures the temperature of the air entering the engine (integral with the airflow meter) c) Throttle position switch - senses the position of the throttle valve d) Coolant temperature sensor e) TDC sensor - measures engine speed and crankshaft position f) Knock sensor (only with Motronic M1.3) - senses the engine vibrations associated with pre-ignition(pinking), which may cause engine damage unless the ignition timing is retarded as a preventative measure g) Lambda (oxygen) sensor (only fitted to models equipped with Motronic M1.3 and catalytic converter) - measures the oxygen content of the exhaust gases Additionally, the Motronic systems comprise the following components: a) Air cleaner - located on the left-hand front wing valance, the casing incorporates the airflow meter b) Fuel pump and filter c) Fuel pulsation damper - located in the fuel line close to the filter, reduces fuel pump noise d) Fuel pressure regulator (preset at 3bar) - located on the end of the fuel rail within the engine compartment, maintains a constant fuel pressure e) Fuel injectors f) Idle actuator (ICV) - controls the volume of air bypassing the throttle butterfly at idle, thus maintaining a suitable idle speed during warm-up and a constant speed when the engine is warm. g) Supplementary air device (models with Motronic M1.3 and catalytic converter) - provides supplementary air to the idling circuit as an aid to starting and warm-up h) Throttle butterfly housing - two throttle valves open simultaneously and the housing is coolant-heated to improve fuel atomization i) Electronic control unit (ECU) - located under the driver’s seat, the ECU controls the system components j) HT distributor - the distributor simply distributes HT current to the spark plugs and consists of a rotor arm on the end of the inlet camshaft and a conventional distributor cap. k) Ignition coil - a conventional ignition coil is used, being triggered by signals from the ECU. l) Relays - injector and fuel pump relays are fitted, both being controlled by the ECU,located on the drivers side inner wing or along with the ECU depending on year of manufacture. m) Idle mixture (CO) adjustment potentiometer - for the Motronic ML4.1 and M1.3 (non-catalyst) systems, the idle mixture adjustment potentiometer is incorporated in the airflow meter casing. Note that on models equipped with the M1.3 system and catalytic converter, no adjustment of idle mixture is possible All Motronic systems function in a similar manner, the differences between systems being of a minor nature, mainly associated with system sensors and the programming of the ECU.
Fuel Injection Full details of the system are available in the downloads section which features pages from the Citroen Manual.
