I saw this on g5 club and thought i would post it.
What you need:
New spark plugs (AC Delco 41 103)
Needle nose pliars (to pull out your spark plug socket when it sticks to the plug rather than your ratchet)
5/8" spark plug socket with a long extension
10mm socket and a short extension (a long 10mm socket might also work)
Torque wrench (low range)
Tool for checking the spark gap on your new spark plugs
Do not attempt this while your engine is still hot. You may damage the threads in the aluminum head.
It takes a long time for the engine to cool down, especially near the spark plugs which are pretty deep in the engine.
Before starting to remove parts, check the spark gap on your new plugs to be sure that it is correct. The plugs that I bought were pre-gapped to 0.043", which was the same as the factory plugs that I removed.
I started with the engine cover already removed.
Use your socket wrench to remove the 10mm bolt that holds down the coil pack.
Gently pull the coil pack straight up to remove it. It will need to unplug from the spark plug, so there will be a little resistance until it lets go. Set it aside.
Use your socket wrench to unscrew the old spark plug. You'll need to use your spark plug socket with a long extension.
My plugs were 93,000 miles old when I replaced them, and they made a lot of loud creaking and cracking sounds when they finally broke loose.
When I removed them, I could see that there was some type of oily fluid on the threads. I think this might have been some lube that the factory used when installing them.
Remove the spark plug.
Put the new spark plug into the spark plug socket and use only your hands to get the threads started. You shouldn't need to use a wrench at all; just use your fingers to turn the extension that you have connected to your plug socket. Stop tightening it as soon as it is nearly all the way in.
Some people will say that you should use a little bit of anti-sieze on the threads, but the service manual says not to. My old plugs were really difficult to remove, but I still chose to not use any anti-sieze.
Use your torque wrench to tighten it to 15 ft-lbs. - That's not much tighter than hand-tight. (You should use two hands on the torque wrench. For the sake of a picture, I only used one hand because I had the camera in my other hand.
After torquing the new spark plugs to spec, my spark plug socket would always stay stuck on the spark plug and disconnect from the extension. If this happens, use your needle nose pliers to pull it off of the plug.
Plug the coil pack pack onto the spark plug, and reinstall the 10mm bolt. Don't over-tighten the bolt. It just needs to be snug.
Repeat for the other three plugs.
Once all four plugs have been changed and the coil packs have been reinstalled, you are ready to go another 100,000 miles with your new iridium plugs.