MB specifies a range of 0.5-2.0% CO at idle for our M117 engines.

But presumably that was for regular gasoline with stoichiometric ratio of about 14.7. The 5-10% ethanol we have in our gasoline provides additional oxygen, so presumably the CO specs would now be different (for E10 Stoic ratio is apparently about 14.1)

Because the wideband sensor doesn't know what fuel we are using, it is really just reading Lambda (measure of excess oxygen) and converting it to AFR (assuming gasoline with no ethanol). If it reads 14.7, that really means 14.1 if we are using E10.

So my question is, what should target AFR (or lambda) be, to be equivalent to MB's original 0.5-2.0% range?

ADDED: No response here, but I probably have found what I needed, just in case anyone is interested.

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5

In the early days of EFI and before that with carbs, manufacturers specified an exhaust %CO as a way of setting the car up. The only kind of meters available read %CO and AFR, (based on conductivity of the exhaust gas?). So even then, they had a way of converting from AFR to %CO.

So, one way to convert %CO to AFR or Lambda would be to get a picture of an old meter and copy the scale!

But, there are several charts that I found on-line . There is one in the tuneup section for old Jags starting on page 109 of this link. They use Lambda, AFR and CO and give a table to cross reference.

There is another table in this MG reference. It is a bit different from the Jag table.

I also found this reference that includes a computer program that would calculate %CO from lambda, fuel composition and engine temperature. Program is called COMBAL and can be downloaded here. But, I have not yet got this to match the above charts. The temperature that is required, must be the temperature in the exhaust port where the CO is still reacting to CO2. But what is that temperature on my old M117 D-Jet ?

The program uses sophisticated method of calculation based on reaction kinetics (that is likely why temperature is needed). I suspect the charts may have been done a different way:

For any AFR, it should be possible to assume all carbon goes to CO and work out how much oxygen that would require. Then use the remaining O2 to convert part of the CO to CO2. The remaining CO is the exhaust CO for that AFR or lambda. Including ethanol adds a bit more complexity, but also doable.

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5