2002 #8 cyl not firing

My mechanic is about to pull his hair out. The #8 cylinder is not firing on my 2002 Continental when in drive. It runs fine in park, reverse & neutral. He's tried everything he can think of and researched on the net with no help in sight. Any ideas? THANKS!!!

Probably a bad coil boot, under the load of the engine/trans in drive, it demands more from the coil, and if there is a break/tear in the boot, it will pass to ground the way with the least resistance. Either that or you've got a bad coil, and it can't handle the load. Take out the #8 and #7 coils and swap them, and check it again. If the problem moves to the #7 cylinder, you know its either the boot or the coil.