I have a 98 Z with 101,000 miles, and was wondering if the cats need replacing now/soon. I am not experiencing any problems (knock wood), but would like to know whether I should think about replacing the cats, or at this point just wait until they become clogged, and do it at that time. Thanks in advance for any help on this matter.

 

Wait on them. Your car has after cat O2 sensors that'll tell you when they fail.

 

My '99 Z28 has 91k on it and the cats start to stink whenever you run it a little bit or after a trip with some stop and go traffic. Is this a sign they might be going bad or getting clogged up?

 

Once they'er clogged you're going to suffocate the engine and stall out. If you think they're bad, they stink, and you got high mileage, I would say look into buying some new ones.

 

As long as you keep the engine in good tune, they'll last a very long time. Ignition related misfires will kill old converters in a hurry.

 

About 75,000 miles is all you can expect, if you get more it's a blessing.