I have a 95 Z28, thats running a little rough. I changed the plugs (wires looked good), but that didn't help. Being in california I also had to get the car smogged and it failed pretty badly, emissions were much higher than what they should be. What do you guys think could be the possible problems? The car is all stock with 95k miles.

 

Since we have almost no details all I can say is that it should be given a good tune up. Which includes:

Cap and rotor, ignition coil, O2's, wires, air filter and fuel filter. ALL of which are considered tune up items.

Consider having the injectors cleaned on the rail.

Clean the EGR and port.

Have an exhaust back pressure test done or unbolt it yourself and test.

FYI you probably didn't bother to look at the wires on the passenger side where they turn the corner behind the alternator. This is extremely tight and the area of problems many times.

 

What were the exact emissions test results for HC, CO and NOx, including the measured value and the maximum allowable value for each?

What does "running a little rough" actually mean - at idle, at part load, at wide open throttle, misfires, stumbling, all of the above?

When you decided that the plug wires looked good, were you looking at them in the dark, looking for signs of arcing?

Have you had it scanned for codes?

Has the catalytic converter ever been replaced?