P0300 Saturn -only the number 4 cylinder miss firing

Question

I have a 2005 Saturn L300, we have replace all the plugs, ECM, fuel injectors, and ignition coil. and we are still getting a miss fire on number 4 cylinder. only the number 4 cylinder and also did a compression check. but can't seem to find out the problem?

Answer 1

P0304 Misfire number 4 cylinder ,

Check the timing belt marks And also is there any unusual sound like a exhaust leak from the number 4 cylinder. ? A compression test is good, do a running compression test on the number 4 cylinder it running comrpession should not be less than 65 psi.