Have you checked the spring inside the coil pack can/is make contact with the spark plug, take it off and look inside (sounds daft but a mate of mine was messing with his loads and part of the spring broke off and it wasn't making a connection)
if you have checked the coil packs and the misfire doesn't move then you can rule them out (except for the above)
plugs checked and same thing.
The only thing I could thing next would be the wiring harness to the number 4 coil pack, its an easy fix, just get a plug online (or on here if someone breaking) and solder the new one on.
A pic might still be useful in case there is something we can see you aren't aware of