How to test a coil with a multi meter

[Rata Road]

Long ago I had a problem with a miss in my Depot Hack and tracked it to one coil not working.
So for several years I have taken one coil from my speedster or my Coupe when I want to drive the Hack.
This year every night I take a different T for approx 45 mins drive around most streets in our small town, so each car gets a good run every 3 days but I was getting sick of the constant coil swap and have now managed to get some more coils.
Yesterday I decided to look up how to bench test a coil lighting a spark plug and to my surprise all coils light the plug including the faulty coil?

Maybe it just needed a contacts clean or the fact I used a 12v test battery as the car is 6v and the mag wasn't very good so I ran the car on battery.
(Mag since fixed using the 3 battery in line spark method), now it runs fine on Mag. I havent tried putting that faulty coil back in.

However I would like to ohm test each coil, I see some you-tube clips showing how but they don’t explain what settings I would need on the multi meter. I have a Fluke meter.
Can someone please explain –
1. Where to take each reading
2. What the reading should be for each particular test
3. And how do I set the meter for each test if the setting is different
4. Also does it matter when doing a bench test looking at visible spark on a good spark plug whether the coil is connected to a 12v battery v a 6v

Thanks
Kevin

[RajoRacer]

I was learned by Ron Patterson that you set your analog ohm meter to 1K - touch one lead to either contact & the other to the other on the side of the coil and the reading should be in the 3200 ohms +/- 10% IF I remember correctly.

[Art M]

:i suspect that the capacitor is defective. This can be checked with a capacitor meter, which are available on line at a very affordable price. I have one and have found that all of my coils needed new capacitors.
They are kind of messy to dig out but after doing several it gets easier. Or you can send them to a rebuild.
Art Mirtes

[Rata Road]

Thats interesting Art.

Steve can you please clarify exactly where you test, lets say one button teminal is on the bottom, two buttons are on the side lets say higher & Lower.

Thanks
Kevin

[RajoRacer]

You test the two side buttons. In most cases, if the coils passes the ohms test it is likely re-buildable.

[Rata Road]

So this test only tells you if the coil is rebuildable? I was hoping it would tell me if the coil is in good condition.

Tell me - If a coil makes a good spark on a test bed spark plug is it possible that this coil wont be good enough in the car?

[RajoRacer]

I have just enough coil knowledge to be dangerous - hopefully Ron Patterson or one of the several "expert" coil gurus will assist you in your quest !

[KBurket]

One of Ron Patterson’s old posts includes a pdf showing the ohm meter measurements.
http://www.mtfca.com/discus/messages/80 ... 1252887023
There’s other discussions, one in Tinkering Tips Vol 2 I believe.

[MKossor]

Here is a video link to the MTFCA Coil Testing and Tuning Webinar I presented last year that you may find of interest. It is a bit long but covers a lot of information. You can skip around to the areas of interest or watch the whole thing.

https://youtu.be/RYcGD-8Ol3s?t=364

Let me know if you have any specific questions.

[Rata Road]

Thanks Kevin,
thats a help.

Kevin

[Rata Road]

Thanks Mike, I'll watch this then get back

Kevin

[Rata Road]

Mike the webinar was interesting but a bit heavy for me.

I see nobody answered number 4 question above but today I discovered the answer myself.
I cleaned the timers on 2 of my T's today and noticed one car wasn't running right so I cleaned the coils/coil box etc but no improvement.
I grabbed a screwdriver and I noticed no 3 wasn't affected when the plug was shorted out.

I fitted a spare plug and lay on the head....turned the crank...good spark.
I removed the existing plug, cleaned it up, lay that on the head and good spark.
So I refitted original plug, started the car with no improvement and still no effect when shorted out.
So I replaced that coil.
Ran nice and when tested I lost a cylinder when each plug was shorted out.

Moral of the story - A coil that can make a spark plug buzz and look good to the eye doesn't mean it will run smooth in the car.

[Matt in California]

I prefer this chart that John Carter developed for simple multi-meter tests:

coil_testing.jpg (72.28 KiB) Viewed 2423 times

Also a couple years back I made the following. I need to update it, but you may find it helpful.
attachment=0]Model T Adjustment 3_7_21.pdf[/attachment]

Matt[

[Rata Road]

Matt, heaps of good info in your attachment.

Thanks

[MKossor]

Moral of the story - A coil that can make a spark plug buzz and look good to the eye doesn't mean it will run smooth in the car.

Yes, indeed; there is a lot too it but well worth the time and effort to learn and understand.

Ran nice and when tested I lost a cylinder when each plug was shorted out.

That test merely indicates each coil if firing. There is a Huge difference between a Model T engine that "runs" and one that runs well. The difference is largely dependent upon on ignition Timing to which the coils play an integral role. Unfortunately, you can't adjust coils to all fire spark after the same dwell Time and do so consistently using a multi meter. You can email me (mictel at comcast dot net) if you would like to know more; I can't discuss more here because I developed and market tools used to make the job easy.

[jab35]

Matt: That's an excellent article. Information like this should be incorporated into the mtfca booklet "The Electrical System" jb

[MKossor]

Matt,

I noticed a few links in your Model T Coil notes are broken due to WebSite updates. Here are the present links to those references:

Reference 5:
https://img1.wsimg.com/blobby/go/f76807 ... 6881770750


Reference 8:
https://img1.wsimg.com/blobby/go/f76807 ... 6881770750


These links should be valid for some time.

[Matt in California]

Kevin,
I am glad that you found this helpful!

James,
As you can see nothing stated in the article is original, but I did find that I had to search around for stuff. I have posted it in the past, but it didn't get much traction. I laugh because no one has called out the $2940 5/16" Head #12-32 Jam Nuts I think that people just havn't looked at it carefully. (The idea with the nuts is that you have to make your own or just by a kit for $1.50 from a distributor, but if you live on the other side of the world that may not be the best option.)

Mike,
Thanks for sending the updated links! I updated the document above. On reference five I was referring to: Electrically Cranked Coil Tester Instruction Manual. You listed the software install manual.

Matt

[MKossor]

Matt, My Bad. Reference 5 should have been: https://img1.wsimg.com/blobby/go/f76807 ... 5263743238