I have a 1995 Acura Integra with ton of miles that runs great but failed smog here in California. Under HC, the numbers are 120 and 90. Under NO, the numbers are 1655 and 1251. Would a new catalyic converter correct my problem? If not, would I have to rebuild the engine?
High HC's are cause by too much raw fuel coming through the exhaust. There could be many things that cause this. Could it be a catalytic converter? Yes, it could, but there are other things to consider especially with that many miles. When I have this problem, I first look at the ignition system. When was the last tune up? Is the ignition producing a good hot spark that will burn all the fuel? Next, are there vacuum leaks. And finally, and most important to you, is engine compression low? For some reason, you are not burning all the fuel that is injected into the cylenders causing a rich mixture. It may sound odd that I say a vacuum leak could cause the issue. One would think that would cause a lean mixture, but it causes a lean misfire resulting in high HC's.
Check those things before replacing the converter. They are cheaper.