How to Test Coils?

[StrnWolf]

I could not find any information on how to test for bad coils for my car so I am wondering if there is a way to test if either of the two ignition coils on my 95 SL2 DOHC are bad but not triggering the check engine light.

[billr]

Sure, the ignition coils could be tested; the ICM under them would be tougher to do. But why bother with any of that until the plugs have been pulled for checking/cleaning and compression has been taken?

To test the coils I would remove them and check resistance across both primary and secondary windings, and resistance between the two, and resistance from either to any metal on the coil case that could ground it. I'm guessing the primary should be about 2 ohms, and the secondary in the 5k to 15k range; but both coils should be about the same. There should be no continuity between windings, or from either winding to a case ground. See? Pulling the plugs and taking compression is much easier, start there!

Functionally testing the coils would require setting up a driver circuit, and even then you probably couldn't test at all common conditions of heat, vibration, or humidity. Much easier to just swap/replace coils to troubleshoot if the resistance tests come out OK and if you don't find some other obvious problem.

[fdryer]

Originally Posted by StrnWolf

I could not find any information on how to test for bad coils for my car so I am wondering if there is a way to test if either of the two ignition coils on my 95 SL2 DOHC are bad but not triggering the check engine light.

Basic spark test; remove fuel pump fuse, remove plugs wires from coils after noting firing order, have someone startup while you observe for spark across both coil towers. Either spark jumps across each coil tower or not. This tests the ignition control module and both coils to produce spark. Replace plug wires and fuse after testing.

[StrnWolf]

Apparently the mechanic who diagnosed the engine did not properly install two spark plug wires. They were just resting on the plugs, so very upset about that. But that did not solve issue. But not surprising. Will post more after compression test!

[StrnWolf]

What would be a good set of coils to buy from rockauto .com other than ACDelco? Or would that be the only good one?

[billr]

I would use SMP (Standard Motor Products), but many here prefer getting used from a JY over anything new.

I wouldn't rush into changing the coils. Simple coils like those are very rugged, especially now that there is no need to stuff a lot of current through a coil trying to drive a V-8 through single coil. In 60 years of wrenching on all kinds of engines, I have never had a bad coil.

[StrnWolf]

Is there a way to test the power to the ICM? A couple years ago when this was my friends car the original ICM connectors were all VERY damaged so I got some good ones from yard and connected them using some clamp joints, BUT dumb me forgot to use shrink tubing. Now that I have time I plan on re-doing the job but soldering the joints together for a perfect connection. But can is there a way to test the connectors now?