How an Ignition Coil Works

[speedkar9]

Here's what's inside an ignition coil and how it works to increase the voltage to fire a spark on your car:

Here's a few photos of the ignition coil.

Starting with the coil, removed from my Toyota Corolla:

An ignition coil is located on top of an overhead cam engine. Its responsible for increasing voltage from the car's 12V to the thousands of volts needed to fire a spark in the combustion chamber:

When chopped open you can see the coil and other layers, along with the center iron core:

Here are all the components inside the ignition coil:

Here's a system diagram of how the ignition coil works electrically:

Note its the voltage spike caused by varying the electromagnetic field that fires the spark, and not just the step up transformer itself.

Enjoy!

 

[CorollaTom]

Thanks for posting - excellent explanation.
Question: In cars with a single ignition coil, the whole engine stops when it fails. With individual coils on each spark plug, if one of them fails, will the engine keep firing on the good cylinders (or will the engine shut down)?
Thanks.

 

[speedkar9]

Thanks for posting - excellent explanation.
Question: In cars with a single ignition coil, the whole engine stops when it fails. With individual coils on each spark plug, if one of them fails, will the engine keep firing on the good cylinders (or will the engine shut down)?
Thanks.

Yes, if the single coil fails then you'll get misfires on all cylinders.

 

[two-if-by-sea]

Awesome write-up!

Yes, if the single coil fails then you'll get misfires on all cylinders.

I can't speak for Toyota, but when I lost a single coil on a 2001 Suzuki and a 2000 Taurus, each time the OBDII told me exactly which cylinder's coil had gone bad, and I was able to limp home. Granted, both times, the car ran like ass, like when an old school engine loses a cylinder. The Suzuki was spewing smoke out the tailpipe, but the Taurus didn't act nearly as catastrophic.

I lost a coil on an old Small Block Chevy, and the car immediately died.

 

[Toyota for life]

Thanks for posting - excellent explanation.
Question: In cars with a single ignition coil, the whole engine stops when it fails. With individual coils on each spark plug, if one of them fails, will the engine keep firing on the good cylinders (or will the engine shut down)?
Thanks.

The other cylinders will keep firing. But you want to install a new coil asap or you will ruin the engine.