Audi A4

since 1994 release

So there is an ignition spark

The basic principle of ignition is that in the beginning current of the accumulator passes through primary winding of the coil of ignition.
This winding consists of several rounds of a thick wire. Under the influence of current around the ferromagnetic core of the coil of ignition powerful magnetic field – energy of ignition is formed.
That there was an ignition spark, accumulator tension on the ignition coil is disconnected. It occurs at the command of the control unit on the so-called "output cascade".
With switching off of current magnetic field in the ignition coil disappears. There is a following:
In the secondary winding consisting of numerous rounds of very thin wire there is an impulse of a high-tension current in several tens of thousands of volts.
This tension goes to that spark plug which just is in line in an ignition order. Fuel-air mix ignites, the engine continues to work. The electric chain becomes isolated again, and the new cycle begins.