I have a '95 Z-28 that will not pass smog. It is failing for the HC at idle. The HC's are at about 300 and the CO is at .7 or so. At 2500 rpms the HC drops to about 70 and the CO stays at about .7, give or take a bit. They tell me that all of these numbers are pretty high, and that it is probably running a bit rich. So far the EGR seems to work, the O2's react, and it hasn't thrown any codes. One of the mechanics at the shop thinks it may be my CAT, which is what my friend thinks too. However, another mechanic thinks that its an electrical issue. I have no idea what to do about this. Any input would be appreciated.

 

check your fuel pressure and the regulator. i failed the hc cound here in mass and it was a broken fuel pressure regulator.fuel was comming out the vac line from the regulator and into to my intake. I just put a new one in yesterday and am going to to see if i pass sometime this next week. i'm pretty sure i will. It might be your cat but usually i would think that all of the reading would be off some not just HC but i might be wrong.

 

Is the car overdue for a tune-up (plugs, wires, fuel filter, air filter)? How many miles on the O2 sensors? How many miles on the cat? The cat is critical to cutting HC emissions. Old oil can also contribute to high HC.

 

Well, when I bought the car about 2 months ago it wasn't running, so my friend and I put a new opti in it, a used ignition coil, new plugs, and changed the oil. The fuel filter looked pretty new, so we haven't changed it yet, and it has a pretty clean looking K&N. The car has 150k miles. The cat appears to have been replaced, but I have no idea when. The plug wires and the O2's look original, and if they aren't then they are pretty old. The computer says that the O2's are reacting, but can the O2's maybe give improper readings?

 

The O2's need to be "bouncing" actively to be good. I think it's cheap insurance to change the O2's (use AC Delco only) and the wires. Chances are a replacment cat is what you need to pass HC emissions.

 

The O2's are active like they should be, but does that necisarily mean that they work?

 

O2s shouldn't give false values, so I doubt it thems. If they stick on one spot for a while or move slowly then thats a problem...you should barely be able to read the voltage on them before they change again.

 

Ok, then it sounds like the O2's are working properly. But how about an electrical problem being the cause for it not passing? One of the mechanics I talked to seemed pretty sure that my problem is an electrical problem like bad coil wires or plug wires.

 

Are you sure that the cat isn't hollow?

 

I have no clue. Are there any ways of telling short of cutting the CAT off and looking inside of it?