[FrugalNinja250]

Originally Posted by greg737

I'd have to have you explain to me how this could be done. A narrow-band O2 sensor only tells you whether you're on the rich or lean side of the "gasoline stoichiometric" air/fuel ratio. It just isn't capable of telling you exactly what your air/fuel ratio is across the possible range of rich to lean mixtures.

Here's a example graph of the information you get from both a wide-band and a narrow-band.


As you can see the narrow-band O2 sensor (blue lines) can only be relied upon to tell you when the air/fuel ratio hits "gasoline stoichiometric" (14.7/1), that's its only definitive datapoint, whereas the wide-band O2 sensor can sense and report any air/fuel ratio from crazy-rich to bone-dry-piston-burning-lean.

So with a narrow-band O2 sensor how could you tune (or use an ECU's "auto-tune" function)? For example, on my 2005 FI project bike my idle air/fuel target ratio is 13.5/1, how could I use a narrow band to tune for that? Another example: for my "tip-in" zone for throttling out of idle at a stop I have targets of around 12.5/1 (which is gasoline's "best horsepower" air/fuel ratio). If my only definite datapoint from a narrow-band O2 sensor is 14.7/1 then how can I tune for 12.5/1?

I'll edit my post to be more clear...