Did you see the post about the Zetec using 2 different plugs for 1,4 and 2,3 or something like that? I'm not sure what the story is on these Zetec plug issues, but cracked insulators seems pretty extreme. There has to be a cause for this
Are you using the same type of plugs/wires/coil that others are using without the cracked insulator problem? I think if the problem were mechanical, you would see/hear where the piston or whatever was hitting the plug....
