Testing a Coil

[vping]

Can a coil be tested with a multimeter? If the answer is yes, how do you do it.

Can it be done on different coils on different vehicles?

 

[dsltek432]

Yes. Try here
www.freeengineinfo.com/how-to-test-an-ignition-coil.htm

 

[RonMacPherson]

Good basic introduction. However the primary resistance may be outside of this sites specs.

Older coils often came equipped with a resistor, resistor wire that reduced coil input voltage.

So, a little research on what your manufacturers/models specs are is a good thing.

(Why did they show a picture of a Honda type distributor when they talk about coil diagnosis?)

 

[gjoakes]

Yes. Try here
www.freeengineinfo.com/how-to-test-an-ignition-coil.htm

A lot of misinformation at that link. If any of the coil windings are open you will not get zero ohms indication (as stated)on your meter you will get inifinite ohms. I spent the better part of my adult life in the magnetics industry designing, building and testing devices and if I were performing a <span style="text-decoration: underline">basic</span> test on a coil with an ohmmeter I would do it thus:

1. check resistance between the primary terminals (the light gauge wire connections). This is not a very conclusive test because it doesn't rule out shorted turns in the winding but you should see a low ohm reading, maybe 1 or 2 ohms. If zero (not likely) then you have a short between terminals. If infinite or very high then you have an open wiinding. CAUTION: when you connect the ohmmeter to these terminals you are applying approx 1.5V dc to the coil and if the circumstances are right you could see some VERY dangerous voltages (instaneous in duration) on the secondary terminal. Make sure it is isolated from human contact.

2. assuming it passes that test check resistance between either of the primary terminals to any metal part of the coil exterior. This should be infinite resistance. Anything less then you have leakage to chassis ground somewhere in the two windings and the coil is no good. This is going to be a common failure mode because the high voltage insulation protecting the windings from the coil's metal cannister breaksdown over time and eventually degrades to the point where there is leakage current.

3). assuming it passes that test then check from either primary terminal to the high voltage terminal. For safety's sake you should jumper the two primary terminal together during this test so there is no chance of an induced high voltage on the secondary (described in #1 above). Anyway you should get a high ohm reading of something over 5-10K ohms. Again this is no guarantee that there are not shorted turns in the winding but if you only get a few hundred ohms on this test you know you have a serious problem.

I would consider this type of testing as just quick and dirty and not very conclusive. Passing it does not mean your coil is good - you've just eliminated the obvious failure modes.

Good luck,

Greg Oakes

 

[dsltek432]

A lot of misinformation at that link. If any of the coil windings are open you will not get zero ohms indication (as stated)on your meter you will get inifinite ohms.

I need to pay a little more attention next time before posting a link. Thanks for catching that.