Spark plug blow out

My 2007 Navigator has been having
problems with a spark plug, I came to you
with this problem. I was advised to check
the coil and that was the problem and why
that one specific spark plug was having
problems. Now, I was driving and the truck
started making almost puffing sound, I
pulled over and had the truck towed home, it
wouldn't go over 40. Today my mechanic
opened the hood and the plug as sitting on
top of the engine. The coil was out of place
but somehow still attached. When my
mechanic tried to hook it back up, after
inspecting it, he couldn't tighten the plug
back in. Is there a tool that works better for
removing or replacing the plugs on this
truck? Anyway, he said it would screw on but
when he went to tighten it up it wouldn't go
in any further and like slip out of place.
Please help.....again,
Thanks Rebecca