Got a misfire. Coil?

HighMileage

Albany,NY
Hey gang,

I was out tonight and instantly noticed at 40mph that my GN wasn't it's smooth running self.

I checked the coils. 14k on two of them. 13.7 on another.

I started it up and pulled #6 off the coil. ...nothing.. I snapped it back on.

Then I pulled #2 off. Blue spark city! Crazy long sparks. I snapped it back on.

Pulled #6 back off. Now it sparks and the engine idles smoothly.

Engage trans-brake and build boost to 5psi. ....smooth...

Im hoping it's the coil and not the module. The coil is original dated 2-2-87. But,the ohms tested ok.

Also,I've got some strange ign wires on there with Bad To The Bone stamped on them from previous owner.

Where should I go from here?

My guess is the module isn't sending power to the 2-6 coil.

Thx.

image.png
 

whitehot1

Well-Known Member
Coil Tower Resistance
(measure front to back, on top) 11K - 13K ohms
(for each of the 3 towers)

Looks like you need a new coil pack. Just a suggestion; it's a good idea to always replace both the coil pack and the ignition module at the same time.
That's what I do, no matter which one goes bad they both get replaced as a set at the same time.
 

Boxcars

Banned
While it can't hurt to replace these components as a pair, it sure would hurt one's pocket book. I've never done this, replaced both, and have never had a problem. Just my $.02.
 

HighMileage

Albany,NY
So is there a chance that the ignition module isn't supplying primary voltage to the 2-6 coil?

If that is a possibility,how would I test the module for that?
 

whitehot1

Well-Known Member
So is there a chance that the ignition module isn't supplying primary voltage to the 2-6 coil?

If that is a possibility,how would I test the module for that?

The auto parts stores can test the module for you. You will have to remove the coil pack from it for them to do the test though. It would be best to call your local parts store to see if they can do it before driving there and maybe wasting a trip. If they can it won't cost you anything it's a free service.
 
Only thing I can add is make them do the testing more than once.

Hand an az test a module years and years go. Didn't fail till the 4th try, then kept failing. Kept killing coils at 30-40 straight driven miles. Not a Turbo Buick, but same principle. Make the module do work and it would fail.
 

HighMileage

Albany,NY
Only thing I can add is make them do the testing more than once.

Hand an az test a module years and years go. Didn't fail till the 4th try, then kept failing. Kept killing coils at 30-40 straight driven miles. Not a Turbo Buick, but same principle. Make the module do work and it would fail.

The module was killing coils?
 
The module was killing coils?

Yes.

Had replaced them both at the same time. Would be fine if it was less than half hour of drive time/appx 30-40miles or so.

Kept having coils burn out. Last fit was on my way up north (Mi term). Made it to Flint, coil failed, misfiring horribly. Replaced, made it almost to Birch run, failed. Made it to Bfe, failed. Had a second coil by this point. Finally made it to the lake. On the way back played the same thing, stopped at the same auto parts stores. Life time warrantied coil. Glad I bought the spare btw. Got me between bfe and the same stores.

Got home barely. Everything checked out.

Took the module in, they tested it said ok. I had searched previously and found a bad module could cause the coil to fail. I made them test that bastid and after 3-4 test sequences it started failing. As they kept testing it kept failing. Replaced the module and stopped smoking coils.

Again, not a TB, but ignition modules can be rude to the coil.

When you look at threads on here, a lot of people say to replace the module and coil at the same time. I can only assume there is the same theory behind it.

Had that vehicle at least another 10-15k after that without issue.
 

626gn

Well-Known Member
A faulty module can take out a perfectly good coil. A Caspers Ignition Simulator can narrow it down (but it needs to be AC Delco) or take it to get tested. This is why if you're not sure its better to change both.
 

HighMileage

Albany,NY
I wonder how the module could burn out coils. Lack of heat transfer? Over-voltage?

That explains why I put 3 new AC Delco coils on my 3300 equipped '90 Ciera,and the misfire scenario is happening again after 10,000 miles. It has the same module/coil setup except the coils are individual.

I've got a new module and coil pack coming for my GN. Looks like I've got to do the same to the other car.

Thanks for the replies!
 
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