5.2. General information about system of ignition and precautionary measure

The system of ignition includes the ignition switch, the battery, the ignition distributor, primary (low-voltage or LT) and secondary (high-voltage or HT) chains, spark plugs and wires of spark plugs. Models with the carburetor or fuel system of injection L-Jetronic are equipped with semiconductor system of ignition (TCI). Models with fuel system of injection Motronic have the system of ignition joint with the Motronic system (Digital Electronic System of the engine or DME).

Semiconductor system of ignition (TCI)

This system has four main components: sensor of impulses, control unit of ignition, coil of ignition and spark plug. The sensor of impulses develops an ignition moment signal for system of ignition. It is equivalent to the cam breaker in the standard distributor of ignition the sensor of impulses every time when the ledge of a rotor passes by a sensor ledge develops a signal of alternating voltage. When the control unit of ignition (knot with the capacitor category) receives this signal of tension, due to interruption of primary chain he creates the spark category.

Time of the closed condition of a chain (ignition coil charge duration) is determined in the control unit of ignition at the rate of the most intensive sparking.

The air gap (distance between ledges of a rotor and ledges of the sensor) can be adjusted (look the Section Check and adjustment of an air gap (TCI system)).

The moment of ignition is regulated mechanically (watch the Partition Check of Functioning and Adjustment of the Moment of Ignition (TCI system)). The centrifugal regulator consisting from the sprung rotating small weights, creates an ignition advancing at increase in turns of the engine. The vacuum regulator changes the ignition moment for compensation of change of load of the engine.

System of ignition Motronic

This system also known as Digital Electronic system of the engine (DME), unites in one central block or ECU (computer) all functions of management of ignition and injection of fuel. The moment of ignition is defined on the basis of entrance signals of load of the engine, engine turns, temperature of a cooler and temperature of inlet air in ECU. The only function of the distributor is to give high-voltage signals on spark plugs. The distributor is installed directly on the block of cylinders. In these systems is absent mechanical devices of an advancing of ignition.

The moment of ignition is determined by electronic control and in the Motronic systems is not regulated. During start of the engine the sensor of provision of a bent shaft (the situation sensor) transmits a signal to ECU and by that the initial point of counting of the moment of ignition is defined. In operating time of the engine the ignition moment continuously changes according to different entrance signals in ECU. Turns of the engine are measured by the RPM meter. In the early Motronic systems the sensor of situation and the RPM meter are located on a coupling case over a flywheel on the left side. In the late Motronic systems the uniform sensor (the pulse sensor) located over a pulley of a bent shaft is installed. This sensor works at the same time as the RPM meter and provisions.

Concerning check and replacement of sensors of system of ignition address the Section Check and replacement of sensors of ignition (Motronic system).

Some models are equipped with the VMT sensor located in a forward part of the engine. This sensor belongs to the block of test service of BMW and is not a part of system of ignition of Motronic.


During the work with semiconductor system of ignition it is necessary to observe certain precautionary measures: