Coil pack 3 and 7 are arching off what looks like the wiring going to the packs, and under #7 to what, I cant see.

Do the coil packs crack on the ends at all?

The long version of the problem.

Last week, I had the ever so slightest miss after 40 miles of driving. happened about 2 times
Today I get more often miss at 20 miles into my drive, and it only got worse the closer I get to work. At my last signal I hear a random tapping from the drivers side of the engine bay with rough idle when I hear the zap.

I let it cool down at work and take a look around under the hood and find #5 spark plug wire has a tiny blister that is crusty. On the way home the car runs fine. I stop by the nearest auto parts store and get wires, plugs and gloves. I replace the #5 plug wire at the auto parts store and go home. 15 miles out, I get a slight miss. 5 miles from home it is getting worse and it is dark out.

I pull in the driveway and pop the hood while it is running. I am watching the coil packs arc, and I can hear it.

I am hoping only the plug wires are fried... I guess I will have to inspect the coil packs as well once I tear into it. Just wondering if they crack on the connection ends, or just fail all together?

On a side note for others with coil/wire issues. I searched out the topic and saw other people reporting a miss once the car is warmed up.

I came in the house for a while (the engine cooled down a little) went back out, and fired it back up with a flash light ready. The arcing was gone. I lowered the hood and let it heat back up. At 228 degrees I believe it was, the fan kicked on. I cracked the hood just enough so the light would stay off, a heavy breeze of very hot air hit me in the face. When that happened, the coils started visually and audibly arcing. So there you go with the super heated miss.

 

I have seen coils go bad and arc but its usually at the coil tower. On a C5 it's really rare. Unless there damaged or have some sort of contamination on the coils that conduct electricity, there fairly bullit proof!
Recommend that you remove the coil and carefully look for arc trails or damaged plastic. Clean the coil with WD-40 and wipe off all dirt, grime and oil. Resist the temptation to UP-GRADE your coils with expensive aftermarket coils. They will provide you ZERO gain. If you see burn marks in the plastic,, it most likely toast!

IF,, you clean up the coil and it still leaks secondary voltage, it will need to be replaced. The coil wires need to fit properly in the coil tower and the rubber boot need to seal properly. You can use dielectric grease in the boots to lubricate the boot and help keep moisture out.

 

Additionally, inspect the plug wires(or replace). I have personally seen arcing between the coil brackets and the valve cover......I would have swore it was a coil, and it turned out to be a loose plug wire to the coil. I've also seen the boots split , that would precipitate the same arcing.

 

I replaced all plugs and wires. When I removed #7 wire from the coil pack, the connector stayed inside the coil (broke off the wire).

All boots were in good condition.

I got it out with pliers, removed the coil packs and found corrosion inside #7. Cleaned them all out. Put it together and drove into work today. Everything is fine now.