General information and precautions (BMW 3 Series E46)

General information

The ignition system is controlled by the electronic engine control unit (ECU). The ignition system is combined with the fuel injection system, and forms a single system with it.

Ignition control is based on information received by the ECU from various sensors (engine load and speed, temperature in the cooling system, temperature of the air entering the engine).

Some engines are equipped with a knock sensor. This sensor reacts to vibrations that occur when the working mixture ignites spontaneously. When detonation occurs, the sensor sends a signal to the ECU, which reduces the ignition advance until the detonation disappears.

All models are equipped with a distributorless ignition system with its own ignition coil for each cylinder. On all engines, except the M43TU engine, the coils are located next to the spark plugs. The M43TU engine has a coil block located on the engine compartment mudguard, from where high-voltage wires are extended to all the spark plugs.

The ECU determines the required ignition timing and the period of the coil's on state based on signals from sensors. During idling, the ECU can change the ignition timing for stable engine operation.

Precautionary measures

Follow the precautions given at the beginning of Chapter 5A.

The ignition system and its components should be checked by a BMW dealer or a service station specialist who has specialized equipment. Checking electrical circuits using universal devices is, firstly, very labor-intensive, and secondly, it poses a danger to semiconductor devices, in particular, to the electronic control unit.