CO is the gas used for mixture analysis. It should be about zero after the cat. Not much use.
It is represented by O2 sensor voltage for electronic calculations. Within the CO range of 0.0 to 1.0 the o2 sensor will give voltages of 0.0v to 1.0v and can be used for mixture correction and analysis. Mixtures above 1.0%CO will all look like 1.0v on an O2 sensor, so some correction is needed to find the range.
The DIY article: evaluating engine controls shows a couple ways to use the KE engine management system for adjusting/reading mixture.
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