Testing An Ignition Coil
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Senior User
Joined: Jul 2010
Posts: 168
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From: West Jordan,Ut
Testing An Ignition Coil
Hey everyone I'm working on my 79 and lost all power driving home today. I replaced the dis cap and router thinking that was it but still wouldn't spark. So I'm thinking my ignition coil needs to be replaced but I was wondering if there a way to test it before I buy a new one. I have a volt meter but what do I need to have it set on or is thier another way?
Believe Nothing
Joined: Jun 2004
Posts: 7,513
Likes: 394
From: W. Central FL.
You can take resistance readings but the only way to tell if a coil or module is good is to replace it and see that the problem goes away. Coils and modules, by design, may work when cold and change when they heat up.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
You can do a quick check to look for open or shorted windings by using your multimeter to test resistance. You can check the primary winding by measuring between the BATT terminal and the TACH TEST terminal; you should see about 1.0 ohm. In reality you will see a few decimal points higher than that (closer to 1.5 ohm) because the lead resistance of many commercial multimeters is significant in this case. You can check the secondary resistance by measuring between the BATT terminal and center terminal; you should see 8 to 11 Kohms. If your meter does not auto-range, you will need to adjust it accordingly.
However, coils actually rarely fail. What fails is the mechanism behind what makes the coil fire. With the coil connected, connect a test light from the TACH TEST terminal of the coil to clean, unpainted metal on the engine. Crank the engine over with the key, and the light should BLINK. Report your results.
If you don't know what has failed, you don't know what to replace. Simple as that. A few diagnostic steps will reveal that information.
However, coils actually rarely fail. What fails is the mechanism behind what makes the coil fire. With the coil connected, connect a test light from the TACH TEST terminal of the coil to clean, unpainted metal on the engine. Crank the engine over with the key, and the light should BLINK. Report your results.
If you don't know what has failed, you don't know what to replace. Simple as that. A few diagnostic steps will reveal that information.
Certified Thread Hijacker
Joined: Aug 2001
Posts: 14,441
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Over 60 degrees (or whatever it was) and after an hour or so of driving, whether non-stop or errands, the engine would start acting up.
Turned out the weird "oil leak" I couldn't trace was actually the coil leaking it's internal oil when it would get hot. Which also would cause an erratic mis-fire.
Stupid coil. Stumped me for the longest time.
Josh
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Senior User
Joined: Jul 2010
Posts: 168
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From: West Jordan,Ut
Alright guys I got it fixed I tested the ignition coil was good so I took off the ignition module and took it to autozone and sure enough it failed so I replaced that and it is up and running again. Thanks for all your input and help guys I really appriciate it.
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