how old is the catalytic converter??if it is original it probably needs to be replaced, my 89 just passed the (aparently acording to one reply) tough ontario emmisions test with flying colours (way under the limits). I had to replce the converter last january as it had cracked where the pipe goes in, but did nothing else except ask my dealer to make sure everything was attached and working, it was and it passed. if you have leaks in the exhaust (even if they aren't noticable by ear) this can affect the results as well.

hope this helps.