Ignition help needed

About 2 weeks ago my 95 Aurora started missing. I replaced the first coil pack (cylinders 6 and 7) with one from AutoZone. The car worked fine for about 4 days and then started missing again. I went back to AutoZone and got 3 more coil packs (mfg by Wells) and replaced them so that I now had 4 new coil packs. It didn't make a difference, the car still felt like it was running on 4 cylinders. I took it into the Olds dealer who dianosed the problem as the ICU (Ignition Control Unit). They replaced it at the tune of $650. When I picked up the car it worked fine for the first 20 minutes. It then reverted back to the original problem. I discovered today that once again the first coil pack (cylinders 6 and 7) is not producing any spark. I discovered this by pulling the wire off the top of the coil pack and saw no arc coming from it. Now I'm wondering if maybe the coil pack is fine (since I've had the original and then the replacement stop working). Is there something upstream from the coil packs that could be going bad which is causing me problems? Any ideas? Since I can't get any spark from the coil pack I know that the wires and sparks aren't an issue so this would not be a solution.

I've heard that bad plugs/wires (ie situations that lead to high resistance) can damage the coil packs.

I've now tried a third coil pack in the same slot and it's not working. So anything downstream of the coil pack is not causing the problem. It's something before the coil pack. I've already had the ICU replaced which the coil packs sit on. I now wonder what is upstream of the ICU that might cause this first coil pack (cyl 6 & 7) not to get a spark.

Here's the deal you may have blown out the ICU again because of the problem that original caused all of your trouble. The ignition module may also be intermittanly failing which is why it may have initially seemed like putting in the new coil pack fixed the problem. I have a feeling though that both coil packs are fine. Coil packs are just a bunch or wires wound around. ICU are complicated (read fragile) integrated circuits.

In general ICU's can be checked at autoparts stores for free. But this may not be true of the northstar. I would call an autozone or advance and check if they do it. Anyways this one should be covered under warranty.

To relate. I had a 91 chevy v8, with distrubutor. May seem far off but the systems are very similar. This setup had an ignition control module which fired the a single coil (which was then distrubted to each cylinder through the distributor). I started having this problem where ever 6 months this thing would go out. (In my case this would lead to a no start condition since there is one coil firing for all cylinders) Anyways it turns out that one time when I removed the coil I did not attach both bolts which secure it to the manifold. These bolts not only act to physically secure the coil but also to provide ground. I had one bolt in leading to a poor grounding condition which would eventually fry the ignition module. The funny thing is though once it went (per say) it would still intermittaly work.

Since you are only frying the 6 and 7 then I would check the 6 and 7 plugs and wires.

Thanks for the info guys. I took the car back to the Olds dealer and they said that they found another module that they needed to replace. They replaced it and things are working fine they say. I also ordered plugs and wireset from gmpartsdirect and will install those later this week. Hopefully I'll be good to go for a while.

I picked up the car and it ran fine for about 30 minutes and then no more spark to 2 of the coil packs this time. After messing around with the wires (disconnecting #6 wire) the other coil pack came back on line. I plan to replace the wireset before taking the car back to the Olds dealer again. I don't know how this whole thing works but I gotta agree with you now that somehow the bad wires are screwing up the ICU which in turn is disabling the coil pack(s). I know that the #6 wire is picking up spark from somewhere else because when I disconnect it from the coil pack I can still get a spark on the other end. Very odd or very bad wires. Anyways, thanks for the persistentence. I'm a believer now. I'll replace the wireset before doing anything else.

Most repair shops does not separate the wires with a wire separator and just leave it hanging wherevent it lays. Sometimes it lays on the exhaust manifold and they don't care. More money from you when you come back for misfire, cross-firing, etc.

I would use a spark plug wire separator, tie wraps to move the wires away from exhaust manifold and away from the engine block (not touching).