My 91 Prelude failed emissions as well, and that was a surprise
to me. Tech claimed that the cat was bad, which seemed odd to
me. I bought a new one on http://www.all-catalytic-converters.com
and it passed with flying colors. I believe it was my NOx that was
too high.

I have also heard of some folks running their vehicles on the open
highway for a bit, then taking it in for the test. Somehow, this lets
them pass. YMMV.

"qslim" <Suckers@suckers.com> wrote in message
news:4e824e45103e4c674b78dfb2afd201e4@localhost.ta lkaboutautos.com...
> My buddy has a 91 CRX Si that just failed emissions for NOx. I'm not
> intimately familiar with this thing, and I don't have it in my hands to
> look at, but I'm trying to help him out. The full #s:
> NOx- 2100 ppm
> CO2- .01%
> HC- 20ppm
>
> I don't think that this thing has an EGR system, so I want to advise him
> of a closed loop fuel control problem. I tend to think that the HC and C02
> are fairly low, possibly indicating a lean condition, but the NOx # seems
> awfully high for that (to me, anyway). He also said that the MIL will
> light up intermitently and go off, with no driving pattern that he can
> discern. He took it to a local chain parts store and their scanner showed
> no DTCs. Thanks in advance for any tips.
>