Test Any Ignition Coil With A Multimeter! (Easy DIY Tutorial!)

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My 2003 Honda XR400R service manual doesn't use resistance testing anymore. Instead Peak Voltage specs are listed which means you need an adapter for the multimeter.

I am getting .389 on the primary is that close enough to .5 ?

Well how do I know if the primary winding is bad or its internal electronics then if a high resistance could mean either is the case?

Tom, I have been watching and re-watching your video on resistance values in small engine ignition modules, specically a 2 stroke module. The secondary measurements on my original module =4100 ohms, while the new module = 2600 ohms. The primary values original module = >30 Mohms ( fritzed?), new module = weird values depending on multimeter scale, 29.5Kohm to 201Kohm to 122 Kohm. I can not rationalize the electronic circuitry impact on the primary readings. Nether coil seems to create spark at my older plug and brand new plug. Any advice here?

You completely disregarded secondary insulation breakdown. The secondary winding can and most times look normal, but at high voltage it breaks down. A multimeter will not show you if this is an issue.

Multimeters arent really accurate in the .5 ohm range. It could be a dead short and you would never know it.
It's better just to swap it out and see

Great video! Well explained and to the point!

Excellent video. Very educational. I have two coil packs I gotta test. I believe one is bad, the other I have no idea yet. I didn't know what to do before this video, but I should be good now. 👍😎👍

Is this only applicable with older units? I ask because I tested two brand new ones yesterday after watching this video. Secondary coil - 5.5k, primary coil 8.5 megaohms. After scouring the web someone said the circuitry in newer ones prevents an accurate reading of the primary.

If a simple coil with no electronics, I have taken a 6-volt dry cell and hooked up a ground to the armature, hooked up a spark plug, and of course, ground it. Then briefly touch the positive connection and watch the spark plug and if it has a spark, it is probably good. Just don't hold the wire on the primary just touch it like a set of points are opening and closing.

Can you add and electronic diagram of the coil spark plug the see all the components? Maybe there is a darlington transistor inside of the coil. Who power the darligton transistor base?

Excellent video. That's more about an ignition coil I've heard from anyone. Thanks 😊

I had my own workshop for 30 years and murphy was a constant companion so more often than not there was more than 1 problem or inconclusive. If I had a buck for every coil I tested that had good values but was crap....in the end I gave up these tests, it is only an indication ie if the coil is crap this will confirm it...or not. The most useful test (and fast) if the motor is running - but has an ignition problem - is to remove the cap from the coil and start the motor while holding (and being very careful) the end of the lead to the plug or earth if you have more than one cyl. The spark should be fat strong and blue and most importantly should easily be able to jump about 6mm. As you are holding the lead you can easily vary the distance and if the spark faulters and or the engine stops as soon as you increase the distance the slightest from the plug you know that either the coil is faulty or there is not enough power (dodgy electronics normaly wont let the engine run at all) - you have to then eliminate the plug first too of course but most often it is the coil. But if the spark and engine is still going strong with sparks an inch long you know the coil is not at fault. The next test is then the magneto coil (or with a battery ignition simply to measure the voltage at the coil - this will be pulsed if the electronics are not in the coil). Also here there is little point in measuring the resistance thru it as what makes these tests so inconclusive is a broken down insulation not bad enough to open or short it but just enough to allow moisture to get in. This then shorts it as soon as voltage builds up - same goes for the ignition coil. So you need a peak voltage meter which can be bought cheap and put in series on your multimeter. This then allows the multimeter to accurately measure the very short voltage spikes put out by the magneto and immediately shows up any problems with power supply as a high enough voltage of about 90 - 200v AC will not build up. You need to confirm those values depending on what bike/other you have as that is just from memory and I am retired now! There are also measuring charts for assessing the electronic parts but they can be hard to get right as they will vary depending on which multimeter you have. Sometimes all you can do to verify those is to employ a process of elimination. The best part of this vid was how he eliminated the TCI part of the coil from the test - well done. Hope this helps someone! All the best from Aotearoa

Hello Mate Will the cause the engine to start idle then when you raise the RPM it dies or hesitates then runs Hard to start when hot

You should also test the leads. resistence in leads ???

Awesome video, great explanation on how to test the coil and where to set the meter. Thanks

awesome man thank you for sharing.

Very good video.

This will not test insulation breakdown.

Do you know what kind of tree that is behind you? It's gorgeous!

Very comprehensive coverage on ignition coil testing - wish I had seen it years ago. I'm thinking I've thrown out many good ones based on faulty testing criteria. Cheers

Buy a 500volt megger to check insulation breakdown resistance.

You sure don't sound aussie

Excellent explanation, I enjoy your channel. I have replaced several ignition coils this year for customers.

👍👍

Superhelpful! Thanks

Great video.

What is the bush/tree/plant behind you? I would like to get one if it would grow in my area. Thank you.

Good video Tom. See you at work sometime buddy.

Another excellent video! As you know, you can test resistor spark plug resistance too. :-)

You didn't state what a normal reading between the kill terminal and HT terminal should be when checking for electronics.

Will tuck this one away for future reference. Thanks for all the info you provide for us.

Good information well delivered. Thank you Tom. I will be referencing this video again and again. I bought a box of coils at auction dirt cheap. $20 for about 20 coils, mainly Briggs Quantum and Classic types by casual observation. I will be testing them to see which are keepers.

Good video, what is that plant behind you.

Excellent

Thanks

Great video, very informative

In this tutorial, you really nailed it.
I can take them, as you usually say, on points:
1) A coil can have good resistivity but in operation, the insulation resistance must be pierced - the multimeter applies a voltage of 9V and in operation the coil must support 15,000V. In conclusion, after measuring with a multimeter, it cannot always be eliminated as a problem.
2) As you say, a coil can be accompanied by electronic circuits. Which are of 2 types: analog and digital. They are already called ignition modules. The coil can be perfect, but the electronic part is defective, and then the measurements with the multimeter are fine, even though the module is defective.
The digital ones have a microprocessor and have an ignition map with advance angles corresponding to the revolutions and for the i500 also the injection times.
I can't mention them all here because a video would come out in letters...

I saved this one Tom I want to give this a try ! Not good at the electrical side of small engine repair 🤷

Great information Tom 👍

Another great video Tom! I have been testing some Stihl coils and I was getting those weird readings. I’ll be sure to check them again.

I’ve tried to pin down “experts“ on exact resistance numbers without success. I’ve watched dozens of videos on this subject and yours is by far the best! That said, a couple of comments I’d like to add. First, although many people call these coils they are technically magnetos. Second, in the list of symptoms there’s one thing missing. If the engine shuts down when hot but is capable of being started once again when it’s cooled down, then that’s usually a dead giveaway, although on rare occasion a spark plug can exhibit the same symptom.
Also, another telltale visible sign is delamination of the layers that make up a magneto. If it’s delaminated then it’s probably best to replace even if it still works because it’s only a matter of time before it fails. A good example is a twin cylinder engine where both magnetos are delaminating but one cylinder is still firing.

Thanks bud. This video is timed well because I've got a saw I believe has ignition issues. This is a big help. May God bless you and keep you.

Nice video Tom! Lots of great info. I need to watch this again.

Good video, good should help people

Well done Mate!!☻

Nice job Tom, thanks for the explanation. 👍

Thank you!!!