[AndrewCologne]

Originally Posted by Glenfield

This thread should help you. Correlates CO with AFR. May be easier to get a hold of an AFR to proxy your CO. Could also do it by measuring duty cycle but I’ve never been able to get a good read on that

https://forums.pelicanparts.com/porsche-911-technical-forum/1003338-co-meter-2.html

Dont know from where those listings are coming from, saying that an AFR of 14.7:1 (means Lambda 1 with gas coming with no ethanol) does result in a CO of 0.0 or 0.1.

With a 3.0 engine at AFR 14.7:1 before combustion, a typical CO result with no cat at the tailpipe is approx. 1-1.2%.
And even here it depends on the exhaust system which could mess up AFR readings. in case of a system using SSI HE's where only one exhaust flow from one side is being measured by the sensor, at least at idle the readings will be off, due to significant less heat and less flow volumen at the sensor compared to an original factory setup where the flow from both sides will be collected and measured before a cat wehre in that area much more heat is present for optimal resulting readings.

https://nineelevenheaven-wordpress-com.translate.goog/abgasregelung-beim-sc/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp
(A link via Google translator, manual translation into english language will follw.)
See i.E. in the article the calibrated CO measure device at the german DEKRA station, ... even there with a Lambda of 1.035 wich correspondens to an even higher AFR the CO results in 0.73.