My understanding is that a car with a smog pump uses a "2 way cat", and the pump is important for the health of your cat converter. The pump allows for further burning of the exhaust before it gets to your cat, or something like that. The pump actually does more than just "dilute the air." Messing around with my 911, I've found that while it easily passes California smog with the pump connected, it would fail miserably with it disconnected. It makes a big difference, I have the exhaust gas analyzer number to prove it!

The later cars without the pump use a 3 way cat, and an O2 sensor.

Just a thought.