The term afr is literally air:fuel ratio. That means it's a RATIO of air to fuel. Like a recipe, 14.7 parts air, one part fuel for gas. LOTS of air, one part gas. Lambda of one. E85, 9ish parts air, one part gas. Less air per gas, so takes more (since the air is constant at your boost target). Lambda of one still.
Problem is the O2 has no idea how much gas you just injected. Was the "one" part of gas a teaspoon or a gallon? It knows only lambda and calculates afr based on a formula for gasoline. It also has no idea how many parts of air your engine ingested. Only how much comes out. I wish people would report in lambda, kinda like I wish we used metric in the US.
And you're right, it's questionable the necessity of the flexfuel monitor. In fact, all major manufacturers did away with ethanol sensors years ago in favor of lambda tuning and accurate fuel monitoring. You can calculate ethanol percent from injector pulse width, fuel pressure, mass air flow (calculated from VE tables vs pressure and temperate) and lambda. Ding ding ding winner winner chicken dinner.
Back to lurking.
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