I gotcha, it's. 1994-97 miata and there aren't a lot of cats left. Such is the life of a classic car owner. >I don't see what any of this has to do with smog t

I gotcha, it's. 1994-97 miata and there aren't a lot of cats left. Such is the life of a classic car owner. >I don't see what any of this has to do with smog tests, and it's not even accurate for all vehicles (pre obd2 has just a single narrow band o2 sensor You mentioned the smog tests, saying if the vehicle can't measure them they aren't worth a damn >If the smog checks are worth a damn it shouldn't be necessary to certify the catalysts; if the cat isn't working, the vehicle should fail its regular smog test. Thats why it is not off-topic. No cars monitor for the smog gasses. That's why Cali uses a special sniffer and a dyno to run a load test. In order to accomplish their stated goal of reducing pbotochemical smog, they must employ a dyno to test under load to monitor the production of nox and hydrocarbons out the tail pipe. The oxygen sensors pre-obd2 were never used in any state for emissions, In my state we did a 2 speed idle test on a dyno which is being retired currently as all required vehicles are now exempt from this test. We still are running oxygen sensors for engine management in every car. They do not sense any smog gasses.