If you have tried it hot, and cold, and it still won't loosen, there is not much choice but to remove the manifold. What tools are you using? It is a 7/8" hex, and a crowfoot, or sensor socket is advised. If you are not slipping around it, and you are committed to get it out, then give it all you got. I have even adapted up to 1/2" drive to break them loose. If it pulls some threads, you can use a standard spark plug thread chaser to clean the hole up.
Tuesday, February 13th, 2018 AT 1:19 PM