Hello friends

I need your help to decide if my ignition coil is good or bad.

The service book says you measure resistance of windings. But this is a static test, we use only the battery of multimeter (9V). The coil can show good resistance off car but at high voltage can have intermitent errors or not enough high voltage. So I ask you how to test dynamic my ignition coil and decide 100% if good or bad?

Thank you.

PS my car has the cylindric type of coil.

Edited 24 April, 201313 yr by dohnjoe

This is a tough one. Normally you need to do that on a test bench that simulates the environment ignition coil (IC) is subjected to in real life. The most important parameter we need to check is the spark energy that an IC can deliver.

The reasons an ignition coil like yours might fail are always bad insulation related. There can be a bad external insulation (cracks, carbonization marks, etc.) that result in spark energy loss to car's ground. There can be also a bad internal insulation (oil loss) that result in intermittent short circuit between windings. Both can generate a misfire condition.

I will have to think about a solution to do those tests on a more amateur level. I presume you don't have a high voltage lab in your garage

Edited 25 April, 201313 yr by adurer

I don't have in Russia a laboratory. It is secret to enter where they make high tension tests on objects.

I was joking, Andrey. LOL. Of course you don't have a HV lab. And I bet almost everything is secret in Russia, including experiments on hu... errr 'objects'.

I came up with 3 methods to test the spark energy of an ignition coil, starting from a simple, amateur level to more advanced ones.

Important assumption: all other ignition system components are in perfect order.

Method 1: it is a visual test and it implies using a spark tester of good quality calibrated in kiloVolts. The tester is mounted in series with any spark plug. Basically if an IC is in top shape, the spark generated can jump across electrodes over a distance corresponding to 25 kV mark or more. The spark must have a white-purple color, and must be consistent (no misses) In case you wonder why we need such a long spark when our spark plug gap is under 1mm, that is because compared to atmospheric pressure, inside cylinder when the spark occurs there is a very high pressure/density to overcome.

Method 2 is also visual but more comprehensive because it gives you an inside view of internal combustion. The tool you need is called ColorTune made by Gunson or other local third parties. You literally look inside cylinder through a glass spark plug and you can decide if your engine runs properly based on the color of explosions.

Method 3 is more sophisticated and involves a chain of Zener diodes and an oscilloscope. Although more complex, it has the advantage to literally 'see' and calculate the energy of the spark, which should be around 90 mJ. All details are HERE.

Edited 25 April, 201313 yr by adurer

Thanks you adurer.

Anybody else have other ideas?

Try another coil.

Try another coil.

Why pay for a new coil because maybe is not bad? I want to know more information about testing car parts. Anybody can replace parts like blind but only few know to find the evidence and then change only the bad part.

Why pay for a new coil because maybe is not bad?

Maybe it is, maybe it isn't. But you don't have any way of testing it, as you don't have an HV test rig.

I want to know more information about testing car parts.

Substitution with known good is the best/quickest/easiest/most expedient way in this situation, short of you having a way of testing its HV performance under load in real-world conditions... which you don't.

Anybody can replace parts like blind but only few know to find the evidence and then change only the bad part.

I've had more cars that you've had hot dinners. A coil is a cheap part, and if you've checked everything else properly, then it may well be the coil. As already said, it's the expedient way of testing it, we're not talking about changing an ECU for no reason, it's a coil, it'll cost you £10 for a pattern one to test it? Hardly going to break the bank.

I've had more cars that you've had hot dinners.

You don't know anything about me. Why talking from above? I said I want to learn how to test an ignition coil. You may have more cars than me, but you don't have other ideas than adurer, and he explained nice to me. I asked this topic to learn new things, not to buy new parts without any proof. This is not always about money, but why don't pursue till I find the evidence, and only then change the faulty part?? I will buy a spark tester and ColorTune from here, and test the coil. I prefer to buy tools than parts.