How to Test an Ignition Coil--OT

[Joe Flanagan]

So today I was driving along in my 22-year-old pickup and it died. I pulled over and started checking it out. To make a long story short, I think I have traced it to the ignition coil. I tested the resistance using a multimeter but I'm not sure I'm doing it right. The manual says that when you test for primary resistance, you put the leads of the multimeter on the positive and negative terminals of the coil itself. You should get 0.4 to 0.5 ohms. I've done this and I get 1.3 For this test, I have my meter set for 200 ohms. There are other ohms settings but they're all much higher. Is this the correct setting for this test?

Also, to test the secondary resistance, they say to put one lead on the high tension terminal (where the wire to the distributor goes) and the other on the negative terminal. You should get 8.5k to 11k ohms. I set my meter for 20k and I get 6k. Can anyone point out anything I'm doing wrong or does it sound right and my coil is trashed?

Thanks for your expertise and good humor and everything else I know will follow.

[Joe Flanagan]

I forgot to mention that I have the coil disconnected and out of the car while testing. That's how I understood the manual's instructions.

[greg g]

I have always tested a coil by putting in a different one. If it fixes the problem, I am led to believe the other one was bad......

I fought Ohms law and Ohms law won

Edited July 8, 2009 by greg g

[Joe Flanagan]

I'll be doing just that tomorrow, since I ordered a new coil. But I am curious about Ohm's Law. I really hope this is it because I don't want to do a whole lot of detective work. I'd rather work on my Plymouth.

[Plymouthy Adams]

it is totally dependent on the meter you are using...if your meter does not have a good Rx1 mode with zero adjust..you may not get an accurate reading..when it died and you had not fire but when cool it did..and if you are using points and not an inductive pickup, then the coil is suspect..if however you have pointless ignition..you could stillh ave a problem in the pickup itself..these can also be checked with the ohm meter but these can defy the low by being heat sensitive and thus when cool conduct..but open when heated...disconnect the pickup..touch the negative side of coil to ground if good spark now and now with pickup..ie the pickup...

[Joe Flanagan]

The problem was in fact my ignition coil. But here's the weird thing. The coil tested bad when I took it out yesterday and it tested bad numerous times yesterday afternoon as I triple-checked myself. It also tested bad at 9:30 last night when I had a friend test it. Today, it tests good. Same ohms as the new one. Is this a thermal issue?

[Niel Hoback]

Possibly a heat problem, but more likely it is possessed of an evil spirit. It enjoys playing with you.

[Joe Flanagan]

Yikes. I should throw the damn thing out of the house, then. It's sitting in my basement.