High hc

hc 517 should be 220 no codes coming up new air cleaner & plugs,can a bad cat do this?

It might help if info about the vehicle was provided; mileage, any oil consumption issues, year model, etc.

It’s possible a bat cat could be behind this but there are too many other things that could cause it. A bad cat, if it exists, may be symptom of another problem.

It would be easier for all if you replies to your original post instead of starting a new own. As Ok said, year, model, miles is important.

My 93 Caprice was 100x over the limit for HC when I took it in for NJ Inspection last summer. Two years before it passed with flying colors.

Evidently if an OBD-I car sits too long in the inspection line the Cat will not be hot enough to work properly. Before I took it back for reinspection, the PCV valve and O2 sensor was replaced ($23 total). I drove about 40 miles the day of the reinspection. This time there was no line and the Caprice passed emissions.

Ed B.

OOPS, sorry 95 chevy pu 5.7 2500, 152k no oil burning or loss


95 was OBD-I, so the cat has to be good and hot to work properly. I had to take the Caprice to the State Inspection facility, the local dealer doesn’t even test OBD-I vehicles anymore.

Ed B.

High HC (hydrocarbon) is misfire, pure and simple…Unburned gasoline vapors going out the exhaust…Timing that is advanced too far can cause high HC readings. A vacuum leak. EGR valve leaking. A burned valve or two…

Thanks ,I did find a vac keak at boot for the pcv valve, also, how do you check the cat to see if its good or bad?