How can you tell if your catalytic converter is bad in a 1989 Chevy S10?

That can be difficult to answer. The symptoms can mimic other problems such as a plugged fuel filter, or a faulty coil. Do this with the windows down, and all accessories (blower motor, radio, etc.) turned off. Drive down a quiet street in your neighborhood, or if you can find it, a deserted street. Stop the vehicle, and then apply moderate acceleration. The truck should accelerate normally, but after a few seconds, it seems to lose power, and if you can hear a hissing coming from the seams of the exhaust, (because of all the built up pressure) then there is a good chance you do have a clogged converter. Some shops use a by-pass pipe temporarily to diagnose this problem. Not a cheap one either, that is for sure.