bmwrepairs: How does distributorless ignition system works on BMW 325?

General Information

Beginning with the introduction to North America in 1992 of the E36 chassis/platform, the Double Overhead Camshaft 4-cylinder M42 and 6-cylinder M50 engines found in the 3 Series vehicles have been equipped with a distributorless ignition system. The ignition timing and ignition advance are controlled by the Powertrain Control Module (PCM) to match the driving, fuel and atmospheric conditions. The PCM optimizes the ignition timing using input from a collection of sensors. The ignition timing can be checked for diagnostic purposes, although it cannot be adjusted. The distributorless ignition system uses one ignition coil per cylinder, unlike the distributor type system that has one ignition coil for the entire system and uses a distributor to dispense the high-voltage ignition to the spark plugs.

The distributorless ignition system, which uses individual ignition coils, operates on the same principle as those on the distributor-equipped engines. However, instead of the distributor's rotation being used to distribute the spark from the ignition coil, the PCM controls the switching of the current through the primary windings for each of the individual ignition coils. When current to the ignition coil is stopped, a high voltage current flows directly from the ignition coil to the spark plug.

The PCM contains the memory for basic ignition timing for different engine speeds and manifold airflow rates. The PCM also adjusts the ignition timing according to engine coolant temperature. The Cylinder Position (CKP) sensor is used by the PCM to monitor the crankshaft speed. A misfire can be detected by the PCM if the crankshaft speed fluctuates.

The following sensors are used by the PCM for ignition timing control:

Top Dead Center (TDC) sensors. These two sensors, TDC1 and TDC2, determine ignition timing during start up and when the crank angle is abnormal

Cylinder Position (CKP) sensor. This sensor detects engine speed

Manifold Absolute Pressure (MAP) sensor. This sensor detects the intake manifold air volume

Engine Coolant Temperature (ECT) sensor. This sensor monitors the engine coolant temperature

Knock Sensor (KS). This sensor allows the PCM to adjust ignition timing for the octane rating of the gasoline being used

Information pertaining to these sensors is covered in more detail in Section 4 of this manual.

Fig. The distributorless ignition system uses a separate ignition coil for each cylinder. The coil packs are located under a trim cover-M50 engine shown

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