Disconnecting Ignition Coils Can Cause Damage

Disconnecting "three wire" ignition coils while the engine is running can cause damage. Three wire ignition coils have the coil driver built into them. Disconnecting them while the engine is running may possibly damage the vehicles computer and or the ignition coil.

For as long as I can remember it has been a common practice to disconnect ignition coils while the engine is running to diagnose misfire concerns. If the ignition coil was disconnected and there was no RPM drop then that cylinder would be suspect. This was not only common but it was accepted. Of coarse the design of "earlier" ignition coils was different and damaging the PCM was not a concern. A lot of these coils where "two" wire ignition coils and the driver was either located in the PCM or an ignition module.

It would be my advise not to disconnect 3 wire ignition coils while the vehicle is running. I found this out the hard way first and then learned about it in school. Always check your repair manual.

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