To find out what I can do about/fix my p0303 cylinder 3 misfire detected

Hi, thank you for your response. I went to the Hyundai dealer this morning to get the P0303 cylinder 3 misfire diagnosed again because the check engine light came on again with the same code. (The first time I went there I was told the aftermarket wires are not good that's why I have the misfire so they replaced the wires with original Hyundai wires). I also told them about the loss/lack of power. And this morning I was told I would need a new catalytic converter, according to them it is related to the misfire. I think they are pulling my leg. Now I don't know what to do besides do the compression check you mentioned. ( I didn't do it yet) Any help on that, Thank you

I find it hard to believe the "Aftermarket wires" were not good. They may not be the higher level of quality as the original manufactures wires but they should not give any problems such as codes or drive-ability problems if they were installed correctly and not damaged in the process. You may have a bad catalytic converter but that test is very specific. If you had a misfire and drove the car you can damage the converter after time. If you are still in doubt I would recommend a second opinion.

Ok, first of all I would like to thank you for your response/help on that. What I did on my own is I removed the oxygen sensor and did a back pressure test. At 2500-3000 RPM the gauge showed 3 PSI. From what I know now after doing some research the cat converter is bad. The gauge should not read more then 1.5 psi on a good converter. So, that means I have to get an other cat converter.