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Q: FAILED SMOG DUE TO HIGH CO (%) on 1990 Chevrolet Suburban 2500

Smog results were...

@15mph - RPM 1753 -
%CO2 Meas 11.8 - %o2 Meas 0.0 -
HC (PPM) Meas 87, Max 134, Average 67 -
CO(%) Meas 5.07, Max 1.34, Average 0.24 -
NO (PPM) Meas 2, Max 1549, Average 681 -

@25mph - RPM 1688 -
%CO2 Meas 11.7 - %o2 Meas 0.0 -
HC (PPM) Meas 82, Max 107, Average 51 -
CO (%) Meas 5.27, Max 1.12, Average 0.25 -
NO (PPM) Meas 0, Max 1514, Average 634 -

This is the second time we've smogged it and it's failed. The first time it failed the visual because of the timing and an unplugged hose. We plugged it in and adjusted the timing from 16 to 0. Now it passes the visual but fails the emissions... What to do? Thanks
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I think it's running a little rich (could be because it's running too cool) and the catalytic converter is not cleaning it up well. You may need an Oxygen sensor. The O2 signal can be checked as well as other inputs. Be sure that the engine's running warm enough, I recommend 195 degree F thermostats for these engines. Cooler will cause problems like this. Get it checked by an emissions specialist or a GM specialist.
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