I went and had an emissions done on my 1990 Grand am. i have replaced the oxygen sensor, timing chain, fuel injectors, manifold, crankshaft sensor, engine module, fuel filter, alternator belt and a few more things. The only thing I haven't changed was the catalyric converter. I put a new muffler and pipe on it 3 years ago. but never chnged the catalytic converter as the guy said I didn't need one. everything passed except the HC ppm the reading was
207 allowed is 174. I noticed when the guy got in and revved the motor black smoke can out of the pipe for a minute and then stopped. Could this be the converter? Also I changed the EGR valve yesterday. Also when the car starts first thing in the morning it stumbles. Could my converter be clogged up?