My wife has a 1995 3.1 Corsica that is having problems I can't figure out. It runs good at idle but when you start driving it and give it a little gas it bogs down and starts blowing black smoke. If you barely let off the gas it jumps up and takes off like nothing is wrong. Going down the road it runs really rough and smokes and if you get on it pretty hard it clears up. I was going to pull the codes on it but the DataLink Connector only has two wires in it. Terminal A and M in a 12 plug terminal. Why are there only two wires here? Is there any way I can check codes at the computer by grounding the diagnostic pin? Can anybody tell me what pin it is? I've looked through all the wiring diagrams I can find and they don't show the diagnostic pin. Please, help!

 

I got to thinking it could be the catalytic converter, so today I got under it with the engine running and hit the cat. several times with a rubber mallet and then revved the motor up and a black cloud came out of the tailpipe. Does this sound like cat. problems?