Ignition system: Ignition
The ignition system comprises four inductive ignition coils, one for each cylinder. The ignition coils are supplied with B+ on pin 1 from the main relay (229), pin 2 is connected to grounding point G7.
When the main relay is activated, B+ is applied to pin 1 on the ignition coils. When pin 3 on each ignition coil is supplied with B+ by ECM, a power transistor integrated in the ignition coil will close the primary circuit where the primary winding comprises relatively few coils of copper wire. A magnetic field now gradually forms in the ignition coil and just as the spark is to ignite, ECM will stop supplying B+ to pin 3 and a high tension will be induced across the secondary winding of the ignition coil.
The time during which ECM supplies pin 3 with B+ and the magnetic field is formed in the ignition coil depends on the battery voltage and the engine speed. The voltage on the secondary side is very high as there is a large number of copper windings and builds up until a spark crosses the spark plug gap. This takes place at approx. 5-30 kV depending on the prevailing conditions in the cylinder in question. The high pressure that arises from high loading of the engine requires a higher voltage compared to lighter operating conditions.
The ignition coils can generate voltages of up to 40 kV.
Four ignition trigger lines from ECM are connected to the ignition system as follows:
- Ignition coil (320a) for cylinder 1 is connected to ECM pin 27(B)
- Ignition coil (320b) for cylinder 2 is connected to ECM pin 14(B)
- Ignition coil (320c) for cylinder 3 is connected to ECM pin 13(B)
- Ignition coil (320d) for cylinder 4 is connected to ECM pin 22(B)
CDM (740) is also connected to the ignition trigger lines but has nothing to do with the ignition itself but is a synchronizing pulse for processing the ionization current signal.