got a 91 gtu and fail smog. i live in california and the results says that its a gross polluter. my guess is that from the results, it could be that i have a bad converter. now if it was my cat, how do i know which one because the vehicle comes with 3 cats. this is my first rotary so anything related to this subject would really help. thanks

 

The main cat (back one). The first 2 are pre-cats, that are only there to aid emissions on cold starts. The main cat does all the work once up to operating temp.

 

Smog tech here. RotaryRocket88 is absolutely correct. Just make sure your main cat is working, and gut the two pre cats for the extra power.

However, sometimes the air pump doesn't like to behave during the smog check and that will easily cause a GP scenario. If you are in the area you should stop by my shop before you go back for the retest.