What else could cause my misfire ?

[804zxkid]

Hey guys im new to the forums! Ive already found a lot of helpful info, links, etc. I really like the site. Onto my situation.
So ive had my 300zx for about a month now. The first 2 weeks it was getting a misfire in cylinder 5 fixed. The problem was that it had an oil leak getting on to the spark plug causing it not it spark. My friend who did all the work changed the Fuel injector, all the spark plugs, and the valve cover gasket. He said it was running a lot better and shouldnt do it again. It definetly feels better, but i want to know, is there anything else that could cause it to misfire in that one cylinder? also could it be the reason my catalytic converters went bad ?

[oomsy9883]

either your spark plug was bad or the coil itself, but oil can be common, causing the electricity to straight to ground and not to jump your plug gap and fire the cylinder, as for could this have caused ur cat to go bad... yes, depending on how long you had the misfire for, you have to think of all the unburned fuel from that one cyl going straight into the cat, and there for probably igniting in the cat because it gets so hot and not igniting in the cyl like it should. over time that will burn out your cat. hope that helps

[mrmoose]

could also be a bad fuel injector or the ptu.... or a dead cyl as in bad compression.

[804zxkid]

It ended up being a old valve gasket. The fuel injector was on it way out too though. As for the cats, could I just clean them? And I've heard about a recall for the ptu, I was also told by a couple people that when they called nissan about it nissan said they had no records on it.

[t.mcginley.jr]

If any of the injectors go bad they could cause the engine to run lean (by leaking too much fuel into the cylinder). Running lean for too long will toast cats. The problem isn't that they get dirty, its that the catalyst structure inside gets destroyed. If you're just replacing the cats, you can buy universal cats such as Magnaflows (~$65 each) and get an exhaust shop to just swap them out. They usually only charge like $50-80 labor.

Old vs new style ptu:
http://tech.aus300zx.com/moveptu/moving ... es/el5.jpg

Nissan did/does have a recall on the old style, but since it's been so long since these cars came out most dealers will just blow you off. Usually however, you give the dealership your VIN # and they will check it on their computer and see if your chassis has any outstanding recalls on it. You might need to call multiple dealerships

[804zxkid]

Oh Alright, should I replace them or can I just leave it like that for now? They don't do smog tests were I live if that helps.

[t.mcginley.jr]

If you don't have emissions testing its not a big deal. Your exhaust gas might start to smell slightly depending how bad the cats are trashed. You can just get test pipes but it might sound too raspy unless you get a resonated H pipe.