3/8 impact gun vs tsb??

[Bill MacLeod]

What I use is Motorcraft Spray Carburetor Tune-Up Cleaner in a 1lb 2 oz (510 gram) spray can. Works great for me, bought it a a dealer across the border.
Sure sounds like you had put enough torque on that plug, obviously you were able to break free the other 7. I recall the back plugs on each side were the most difficult to get out.
I used a 1/2" drive torque wrench the first time changing plugs set to 33 ft lb. Brake free approx 1/8 to 1/4 turn, cleaner to top of plug hex, let soak for 1/2 hour, work back and forth much just like cutting threads with a tap. All with engine at around ambient temperature. (75 to 100 F)
You might want to try a 1/2" drive torque wrench. Will have lots of leverage. Beg, borrow or buy one if you don't have one. Its a tool that has many uses.
Anti-seize on the new plugs?

 

[ScubaSteve613]

1/2 torque wrench will be tried as well. Anti-seize applied to other plugs, but had to make sure it was the high temp silver anti-seize as the other stuff just melts right off.

 

[4pullingGM]

I've always had good luck with the 3/8's impact method. I was skeptical when I first heard about it, so I tried it out on a blown up 5.4 3v with over 100k miles on it and original plugs, and every single one came out with out incident. What seemed to work for is the engine cold to warm, not hot. Steady, medium throttle on the impact, not full throttle. Once it starts turning, don't stop. Keep steady, constant throttle input. I had a pretty good reputation with these when I worked at the dealer, other shops would bring these in for me to do. Before I started using this method I had real good luck with the Lisle tool. I also would anti seize the threads on the new plug as well as the the smooth part that stuck down into the head. And use a torque wrench to properly torque the new plug. Hope this helps somebody.