Teach me about ignition coils

[JammerX19]

Looking to improve my understanding of how the ignition coil, control module and distributor all work together to create spark. Can someone help me out here with layman's terms? Ultimately, I'd like to know how the car behaves when these things start to go.

[4uall]

these MOSS guys have good videos (many different videos on this)

http://www.youtube.com/watch?v=rJYJ3KvPhhY

[majicwrench]

Current runs from battery, thru primary winding in coil, thru ign module to ground. This build a mag field in coil. PU sends signal to module as it gets triggered (dist shaft turning), which causes module to open the circuit thru coil. Mag field collaples, creating voltage in secondary windings of coil. This volt looks for a place to go, only place it can go is out coil tower, thru coil wire, rotor, plug wire, plug, jump gap to ground. Now as dist spins, PU sends signal to module, module grounds primary windings in coil, mag field builds, .......
Tis simply stunning that this can work so well, so fast, for so long.

Most electronic ignition systems either work (car runs) or they don't work (car dead). Coils are extremely simple and dependable, despite them being the first thing everybody changes. PU and Module can and do fail.
Keith

[JammerX19]

Most electronic ignition systems either work (car runs) or they don't work (car dead). Coils are extremely simple and dependable, despite them being the first thing everybody changes. PU and Module can and do fail.
Keith

That's a great explanation, thank you. So my next question is: if I wanted to buy a replacement coil, what do I look for? Do they have voltage or current ratings that must be matched? It seems like the Marelli coils are $$$ and I see sub-$50 coils with good name brands on them at the parts stores. Wouldn't one of them work instead?

[supplyguy]

Was wondering same thing. Thanks for asking Jammer and looking forward to responses.

[majicwrench]

In my humble opinion people waste more mony on coils that anything else. The stock coil works wonderfully. Big $$$ fancy yellow-or-whatever pretty color coils can theoreticly produce more voltage, but that doesn't add up to squat. You only need so much secondary voltage to fire the plugs, and the stock coil produces that just fine thank you.
Why do you need a new coil?? A replacement coil in a perfect world would have about the same primary resistance as the OE part, and be designed to work with (or without) a ballast resistor, just like the OE part.
Keith

[JammerX19]

Why do you need a new coil?? A replacement coil in a perfect world would have about the same primary resistance as the OE part, and be designed to work with (or without) a ballast resistor, just like the OE part.

I'm not looking for an IMPROVED or high-performance coil. I'm looking for a SPARE coil. I'd be just fine with stock if there weren't so expensive.

[majicwrench]

If you just need a spare, go to whatever parts store and get whatever cheapy coil that they list for your car. But to repeat, coils almost never fail. A coil is the last thing I would carry with me.