How do you get a sparkplug out that has self welded itself in a 89 grand am engine. 5 tools broken trying to torque it free. May be possible head damage. Runs good for awhile then starts to bog down misfires and dies. Sits for a fewminutes fires up runs for awhile longer same thing
Corrosion isn't usually the problem, but you might try a liberal application of Mopar Rust Penetrant. The stuff works really well, and even faster if the engine is a little warm. It will bubble and sizzle and frees up just about anything, but you have to wash it off well when you're done because in my experience with front end parts and alignment adjustments, if left on, it promotes moisture following it in which makes the parts even tighter the next time. The GM dealer most likely has the same product under their own name but I'm familiar with the Chrysler product. It was developed for rusted heat riser valves in the right exhaust manifold in the '60s and '70s. In my experience in tv repair and antenna system installation and repair, this stuff will free up old rusted tripod bolts in ten minutes that would take WD-40 all weekend.
Be sure you're using a quality six point socket. Impact sockets are made from a softer metal and are less likely to crack. Don't use excessive force or an impact wrench because if the spark plug won't unthread with normal force, by tugging harder you'll peel the threads out of the head. If that happens, it's even too late to work the plug back and forth to free it up. The threads will already be damaged.
One trick I've seen work but never tried is to find a piece of pipe that just goes over the hex nut of the plug. Electrical conduit is what I saw used. Use an acetylene torch to heat the plug. Heat it only near the terminal but long enough for the heat to travel to the threads. A propane torch won't get it hot enough. The engine should be cool too so the shock won't crack the head. The goal is to get just the spark plug hot enough to expand without also getting the head too hot. After heating it for two or three minutes, quickly place the pipe over the plug and pour some water into it. The sudden change in temperature will shock the plug and shrink the threaded section. Get the socket and ratchet on it right away and try to loosen it.
Some people have luck loosening stubborn plugs if they do it right after driving at highway speed when the engine is real hot.