Grounding Ignition Coil Using IGBT ckt....Not Working + Can't Understand?
There are multiple things wrong with that circuit it not only cannot work but it would probably burn out your ignition coil.

The high-voltage that occurs when the switch opens is required - it is that high voltage that gets transformed to the high voltage needed to cause a spark. Putting the 4.7uF capacitor to ground will stop that high-voltage and so stop the spark.

Turning on the IGBT will stop the spark but the current in the coil will then rise to a high level and most coils are not designed to be driven directly by 12V for any sustained period. It will overheat and probably burn-out.


Turning off the power from the +12V could work or another way might be to put the 4.7uF in series with the IGBT rather than across it. This will stop the spark but not cause a high DC current through the coil. Are you sure there was not an error in the original circuit?