What Do Spark Plug Coils Do

All ignition systems for modern petrol engines use ignition coils for the same basic function: to create the high voltage required to produce a spark at the spark plug.

What happens when a spark plug coil goes bad?

If an ignition coil is not working properly, your engine will likely misfire. A misfiring engine results in a jerking or sputtering feel when you are moving at normal speeds. When you stop, a misfire from a bad ignition coil may cause your vehicle to run roughly, vibrate or shake.

How can you tell if an ignition coil is bad?

1. Plug the tester into the coil.
2. Attach the ground wire.
3. Plug in the coil connector.
4. Adjust the spark gap to the correct measurement.
5. Start the engine.
6. If there’s spark, great, it works! If there’s no spark, it’s a bad coil.