91 CRX Si emission tips needed.

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.

 

================

Check the PCV against a known good one. Or at least blow thru it both
ways to be sure it's regulating.

'Curly'

 

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.