Good theory, I like it, should I be looking at the big three parts stores or am I gonna have to find a better equipped shop?

edit: Wouldn't the simplest test be to pull one of the misfiring plugs, stick it on the wire and watch for spark with the engine running? If the spark misses a beat the replace the oldest part in the ignition system, the ICM. Everything from the coils on is new. if the plug isn't missing a beat then check air, fuel, and timing right?

 

Any chain auto parts store should be able to do the test. I know my local AutoZone can. But I would advise having them check all the coil positions on the ICM to rule out an anomaly or isolated failure (usually they just want to test one position).

As for the test you are proposing which is a bit old school (using a plug and grounding it out to validate spark). It is good, but I would not do it on these cars. Too many electronics if something arcs where it should not. You could however use the inline spark testers sold at Harbor Freight.
I would still start with the part store bench test. It is safe and controlled. If it fails on the bench, then I would believe it. If it passes on the bench, I would not 100% believe it but see what happens when you put it back in and see what changes take place just by removing it. Also, those bolts suck on the coils (I usually use a 5.5mm socket to remove them). I have replaced ALL of them on all my cars with standard hex head stainless bolts.

 

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Well, I pulled the #5 and grounded it to the tower brace on the driver's side, and I didn't EMP the car lol. I can tell you I'm 100% sure that the spark is not consistent, it varies in strength and is either doubling up, or skipping every other spark (and it seems to occasionally miss a few in a row) I'll call my AutoZone and see if they can run a test on it just to be safe though.

 

My experience is that the coils on these cars rarely fail. They last an incredible amount of time. I would more suspect the ICM before the coils. Plus, you did the test of swapping the coils and things actually got weirder and made less sense. It makes me lean on a bad ICM. Now, if you had another GM that used the same coils, you could go one step further and full swap the coils with another car (I happen to be in that position).

 

These are actually the ZZP coils and only have about 4k miles on them. My oem coils have been out in the rain but I'll clean them up, install them and see if anything changes. My guess is that the high voltage coils might be drawing more power from the ICM and killed a part that was already on its last leg.

 

I know of the ZZP coils, but I don't know anything about how good or bad they are in comparison to OEM. If I understand, you are on a 3400. If so, my 3400 Grand Am is running the L67 SuperCharged coils (aka "The blue plugs", as the plug is blue on the underside). Not a bunch of difference, but for the junk yard cost it was worth it.

 

As it turns out, the coils did in fact fail, at just three months old and 4000 miles, oh well, oem coils are back in place and it's on to the next issue.

 

Ugh, that sucks! The failure rate of aftermarket 3800 ignition stuff is absurdly high.

 

That sucks, but at least you found it. I stand by a statement I said earlier, I find OEM coils, very trust worthy. Even junk yard coils (which I have two L36 3800 Montes and a 3400 Grand Am running junkyard L67 coils). Heck, I rather salvage an OEM coil these days over an aftermarket. I have seen OEM coils last almost forever (note the word almost) and aftermarket replacements fail in less time than the OEM.
I do hope for ZZP you happen to have a rare failure.

Now.... How did you ultimately find it? Did you just swap the OEM coils back in?

 

Same. Ive got 3 L67 coils on the spare parts shelf that I snagged from a junkyard on one of their half off days years ago. Had no need for them at the time, but they were dirt cheap and the junked cars were relatively low mile (plus we had 3 3800 cars at that time).