I have a customer's 1998 camaro with a 350, ls-1.
it is misfiring on #4 only when at operating temp.
SO FAR is did a compression test cold ...ok
changed the spark plug and wire...
swapped the injector and coil with #2 and still has a misfire ,
only #4...
cold it's does not skip, and runs great COLD.
no ticking or smoking.

Any idea's

Please welcome!!!

 

Bad lifter??? It could be a short in the injector harness or coil harness. Trace them back and see if there's a suspicious spot on either.

 

It's actually a 346 LS1

Yeah, sounds like a problem with the wiring harness or a bigger mechanical problem like Al said. Pull the valvecovers and take a peek.

 

Possibly the #4 Coil its self I've seen coils work fine until the get hot, swap the # 4 coil with another of the coils and see if the problem moves to that cylinder

 

oops sorry I didn't see that you had already done that!