I have a brick that won't pass emissions in Texas. It passes HC and NOX but fails CO. Here are the numbers:

HC(ppm)- Spec/reading - 162/72
CO(%) - Spec/reading - 1.04/1.29
NOX(ppm) - Spec/reading - 576/1163

The tests are run at ~2000 rpm.

Here's the history:
Never failed emissions in the past. '03 reading HC 128, CO 0.34, NOX 974.
Starting running very rich in May 04. AMM replaced. Fixed the problem. Car runs great.
Failed first emissions test in Aug. Replaced O2 sensor, cap, rotor, plugs, FPR, set timing, checked idle switch and temp sensor. I put the O2 sensor on an o-scope and it crosses over from 0.2 to 0.7 volts. It does seem to spend more time above .4 then below, but it does seem to make about 6 to 8 crosses in 10 sec. I can adjust the AMM to get the LED test point to go from "off" to "on/off" to "on". Though I can't see a lot of change in the O2 signal when I adjust it.
Failed second emmision test with almost identical numbers.
I am really stumped.
What is the LED test point indicating?
Could it be possible that the catalytic converter was damaged by the rich running engine? If so, wouldn't the other pollutants have also failed?
Could the replaced AMM be bad?

I could really use the advise of an ECU/emmisions expert to help figure out where to go from here.

Thanks for you help.

John Brady
'86 240 180K