9-3 FWD (9440) L4-2.0L Turbo (B207R) (2009)
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The ignition coil contains a transformer (ignition coil) and a power stage that is operated, triggered, by ECM.
When ignition coil pin 3 is grounded, the power stage conducts so that current can move through the ignition coil's primary winding. When the
conduction is no longer grounded, the spark is fired.
Thus, ECM determines both ignition coil charge time (cam angle) and ignition angle. The ignition coil also contains circuits for ionization current
measurement.
One end of the secondary winding is connected to a voltage source of 80 V. Thus, 80 V runs across the spark plug continually, except for when the spark
is fired, as voltage is then considerably higher.
The existing pressure and temperature in the combustion chamber cause the gases to ionize, which means that current begins to flow across the spark
plug gap without a spark being generated. The degree of ionization determines how much current can flow across the spark plug gap. No combustion
means there is no ionization. Knocking produces extreme ionization.
Ionization current measurement makes it possible to measure existing pressure and temperature in the combustion chamber. This information is used for
