Just put new wires(not motorcraft) and plugs on several months ago. I went and pulled a trailer a couple times lately. After the last time pulling it on the way home with no trailer on the #4 plug wire blew off. seems to do it on decellerating. I have crimped it several times and doesnt help. I did have an antifreeze leek above that plug but i tightened it up and checked again lately. It blows it pretty hard out of the hole and behind the block. Any ideas?

Buy a new wire.

You may also have a bad plug, which is leaking compression gases around the insulator. So replace that spark plug, too.

[q I did have an antifreeze leek above that plug but i tightened it up and checked again lately. It blows it pretty hard out of the hole and behind the block. Any ideas?[/quote] What hole???? You overheated maybe? head warped/cracked/other related boo-boo. Water does not compress. Your plug hole threads stripping out is a possibility.