Ok just spent hours checking parts and found the culprit to this code in my 1996 Hyundai elantra.
Micro fissure cracks in the ceramic of the spark plug. This was noticed while cleaning the plugs. Changed plugs and still had a misfire and code.
Little more testin of cylinder compression, IAC cleaning and checking, ignition block testing, fuel filter check, fuel pump filter check, plug wire check, spark plug gap anf cleaning and checking, and was in in the process of getting ready to remove catalytic converter when I had a thought all this could be some simple vacume leak. Checked PVC valve.
Well what do you know bad PVC, changed it and the car runs great.
So over cap code P304 Cylinder misfire - CHECK YOUR PVC VALVE!
I felt like an idiot after spending 5 hours tearing everything down and testing and was at wits end and about to pull the cat.
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very good Tar Heel Person!don't feel like an idiot.yeah you spent 5 hours cleaning and testing,and found it!some folks would have just replaced all that stuff that you cleaned and checked,(except for the pcv valve),and most would have taken it to the one and only (DEALERSHIP)!!!just think of it this way.how much money did you save?if anything pat yourself on the back.YOU DID IT THE OLD SCHOOL WAY!!and most likely will help someone else when they get on here looking around for a similar problem.it cost you 5 hours of time and the cost of a pcv valve,not too bad.
