Is there a way to use my O2 sensor output (mV) to determine what my air fuel ratio is?

 

you can get a ROUGH estimate from it, when you're not in closed loop and the O2 is hot enough.

 

do you know conversion from mV to AF?

 

i use the hottest line, since i prefer to use heated O2s. using tunerpro to do the conversion for youis much easier though.

 

Sweet! So how do you actually get Tunerpro to display the AFR rather than mV?

 

simpler than onemight expect....

just make a lookup table and make these entries:

a/d counts AFR
23 17
45 16
68 15.5
91 15
113 14.8
136 14.6
159 14.4
181 14.1
204 12.5
226 10.9

now, make a another value, have it use the O2 byte as a reference, send the data to the lookup table, and tunerpro will interpolate anything from a 17:1 to 10.9:1 AFR.

i have another chart for NBO2 to AFR, but i don't think it's very accurate.... says the crossover for 14.7:1 is 350mV.... i've always seen it somewhere between 450 and 550 mV...

also, those numbers are assuming an O2 conversion of X*4.42

 

wiggin, There are a handful of charts & conversion formulas you can use.
I would inquire as to what end you might find that info useful,
seriously.
Lots of us have worked this angle (some for fun) and with a very rare exception end up dependent on a WB for all the AFR's.
I'm not trying to blow you off, just the opposite.
Trying to save you some time.

The fact is NB o2's don't allow very accurate tuning far from 450mv.
So anything under 300mv or over 700mv is pretty useless.