I'm at a loss here guys. My son bought his first car a 03 pt Cruiser Gt 4 cylinder with about 80,000. We knew it need a little work but nothing major and there were no check engine codes. Well a misfire on cylinder 4 code came up months later so I figured I'd take care of it for him. I've had the coil pack, plugs and wires, injectors and cam sensor all replaced on at a time and that code is still there. Unfortunately I live in an area with emissions so this has to be taken care of but neither I nor my mechanic can figure out what do do next. Please any suggestions will help. Thanks in advance.