Hi Twisted6 . . .

Dyno testing is designed to simulate road conditions. Under the 90's standards most cars could achieve what is called a 'Fast Pass' based soley on a sample of exhaust at idle. Only if the car fails the idle test is it put it on the Dyno.

Once on the Dyno the operator takes the car through a series of threshold tests - hold 25mph - hold 35mph - hold 45mph etc. This gives the catalytic converter a chance to heat up and do its job. This allows a car that is a polluter at idle to pass because it is OK under load.

In the case of my MR2 - it puts out to much HC at idle to Fast Pass. So I end up on the Dyno. The catalytic works fine at reducing HC emissions under load. Trouble is that the engine's combustion chamber design causes it to accumulate carbon which raises compression ratio. The result is NO emissions (nitrous oxides) which are a no-no from the EPAs perspective. And the catlytic cannot fix NO emissions. So my readings go up-and-up every two tests and then I need to have the carbon cleaned out before I can pass. GM sells a dissolver that one can pour in through the spark plug holes. The car is still serviced by dealer (where I bought it new ). They clean out the carbon with this solvent and I pass.

I just barely passed in '00; failed in '02; passed in '04 and just passed in '06. I expect I'll have to get the carbon cleaned out before my next scheduled test in '08.

regards,
Keith

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