E10 Stoichiometric AFR & O2 sensors

Stoichiometric is the mixture that most complete combustion happens of both Air and Fuel.
AFR, or the mixture ratio of parts of Air per 1 part of fuel is how the engine computer determines how much fuel to inject after calculating the amount of air the engine is breathing in.
100% gasoline has a stoich AFR of 14.7
Add 10% ethanol, and the stoich AFR changes to about 14.1.
So what does that mean to our oxygen sensors? Wide band, narrow band?
Actually, nothing really.

All O2 sensors measure stoich, rich, and lean. They have no way to determine fuel type, or AFR for said fuel type.
This may be easier to think of in terms of lambda. Lambda is a scale of stoich.
Stoichiometric is lambda 1
Values greater than 1 are lean, while values less than 1 are rich.
This doesn't matter if you have E85, 100% gas, diesel, ECT.

Lambda is lambda is stoich.

Most wideband gauges display AFR, but what they are really telling you, is the AFR for the lambda reading based on 100% gas 14.7= λ 1
So when tuning with a wide band you should still target 14.7 on your gauge, because what it sees is λ 1
To get the lambda value for an AFR, the formula is AFR divided by stoich AFR
For example
14.7 / 14.7 = λ 1
12 / 14.7 = λ 0.81
15 / 14.7 = λ 1.02

To get AFR from lambda, you simply reverse the equation.
Lambda multiplied by stoich AFR, or
λ 0.81 x 14.1 = 11.4

What this means for tuning.
If you change the stoich AFR in your tune to 14.1 for e10 gas, and want to target 12 AFR for your power enrichment on your wide band gauge ( λ 0.81 ) mathematically you should program PE to 11.4 AFR

What if we leave stoich AFR at 14.7?
If tuned to no AFR error at stoich, 0 fuel trims, BLM 128, you may find your open loop AFR's off when not stoich. There are different ways of dealing with this. You can simply change commanded AFR until you get the desired results by how much % it's off.

Reason for not changing stoich AFR,
Most wideband gauges are set up for 14.7 = λ scale. And is configured as such in data streams for data logging. If you set up an AFR error pid, with pcm commanding 14.1 and data stream 14.7, you will be off when in tune. You can setup your data stream to report λ = 14.1. This would probably be the most mathematically correct, but it's alot easier to leave the data stream alone if it's reported correctly at 14.7 = λ.

If you have your tune dialed in on 100% gas, and are changing to e10, you can simply change the injector constant a little richer.
I suppose you could do the same starting from scratch, which maybe the easiest way to do it.

The main take away is your fuel trims and wideband gauges only read stoich and a scale of it. If you target 14.1 on your gauge , you will be rich.

On some of the newer vehicles, they use what is called an equivalence ratio that is FAR. FUEL to Air Ratio, and is the opposite of lambda. 0.9 is lean 1.02 is rich, but 1 is still stoich. In this case all values are based off of stoich AFR value, and do not need further editing.