Does anyone have a little table that shows the Co2 vs AFR ?
Or something like that so you can tell if your rich or lean from a smog test & by how much?

 

there are general tables that show the % gas concentration floating around. Even the O2 isnt a good indicator of AFR under some conditions or if there is a problem, so Im not sure how useful it would be...

 

Yep. While the O2 is good for indicating A/F ratio on a good running engine, you really need the four main gases to determine what's going on for diagnostic purposes.

This is a pretty good site that explains all of that...

http://www.autoshop101.com/forms/h56.pdf

 

CO is a pretty good indicator, when on the rich side. 5% is about 12.5:1. ~0% is lean (or stoich with cat). .5-1% is close to stoich, if no cat.

CO2 would have to be compared to O2, but about 15% is about stoich with cat, and richer is less, not sure how close of a match it is to A/F, but it's not too far off. I'll do a quick check on the chassis dyno tonight with the EGA, and report back. I'm kind of thinking CO2 changes inversely about 15 with CO, like they just trade with each other to add up to about 15. I don't remember off hand what the balanced equation is.

 

CO2 is a good indicator of combustion efficiency, IF measured before the cat.
The theoretical maximum is around 15.5% CO2, the rest being pure Nitrogen, and water.
After the Cat, you should see high CO2 regardless of what's going into it, if it's working.
It won't tell you much about AFR, though.
What will, and quite accurately, is the ratio of CO vs O2 before the Cat.
It isn't quite linear, though. The link previously mentioned has some pretty good charts that can be interpolated pretty close.

 

Like this?

 

Hi Z69,
This link will show not the CO2 % but the CO%
Perhaps help.
http://www.bridgeanalyzers.com/Docum...Paper%2017.pdf

I will look for the CO2 % vs. AFR.

Do we have new nice ideas coming?
Do we need to remove the O2 sensor for a nice cheap CO2 sensor?
Well that would be a nice jump in the tuning world!

Here is the formula of the relation of the combustion gases.
http://www.bridgeanalyzers.com/Docum...0Paper%209.pdf


Regards,
Cobra289

 

Yup ! That's the one.

Bet you will not find one.
CO2 is a good indicator of combustion efficiency, but not AFR.
( gasoline, propane, paper, ex-wife, matters not )

Would be nice, but ( trust me ) I searched. Oh, boy did I search.
CO2 and/or water suggest the best that can possibly be gotten.
There are no cheap sensors for either that can withstand the heat at the tail pipe.
Still, they will indicate combustion efficiency, which is not torque, nor horse power.
( but it is a good start )

What would be wonderful, would be to keep the ( wide band ) O2 sensor, and add a CO sensor !
Between them, you can easily see AFR.
So, I searched for a cheap CO sensor. Found nothing usable.
Even a cheap two gas analyzer that measures THESE two gasses would be nice.

What I did find, was obsolete thermistor technology, which I bought.
It can be calibrated for either, but not both, OR it can be calibrated for the composit result,
which I plan to do shortly.
It also can not withstand the heat at the tail pipe, but it needs such a small sniff that it can work, and did in some 70's and 80's vintage analyzers.
Do a google search for Heathkit CI-1080.
Simple, elegant, and effective.
Now, to make it work...........