General question about E38's AFR/Eq Ratios

[granatl]

One of the tables in the E38 (etc.) has the various AFR's for mixes of gas & ethanol. I have converted my turbo 2010 Camaro to use E85 and rather like the results. However, I question how the Eq Ratio (Alcohol) is being used. I understand that there's interpolation between the Eq Ratio (gas) and Eq Ratio (alcohol), as controlled by one of the other tables.

This is where I'm getting confused. For argument sake, let's say that I'm running 80% alcohol (as measured my the FF sensor) and the AFR for alcohol lambda is 10.8 (I don't have the exact number in front of me). Does the computer correctly take the 10.8 AFR / 1.35 Eq ratio and target 8 AFR (which would be very rich)? My wideband numbers don't seem to correlate this. OR... is it using the left-most cell in the AFR table (14.6xxx) and applying the eq ratio against that one?

[DSteck]

I think you're getting tripped up on AFR vs. lambda. My advice to you is ditch AFR as a metric and learn to think in lambda.

14.68 on gasoline is 1 lambda.
9.765 on E85 is 1 lambda.

At 80% alcohol, the stoich table defines what the ECM should base calculations off of. From there, it'll take your desired EQ ratio (for whatever reason, EQ ratio in the editor is inverse lambda, but commanded EQ ratio in the scanner is based on lambda) and calculate how much fuel to use. With 10.8 as stoich and a 1.35 commanded EQ ratio (0.741 lambda), you'll get 8:1 AFR. That's the actual required ratio of air mass to fuel mass needed to achieve 0.741 lambda.

[granatl]

Thanks! I do lots in lambda. Then I remembered something you noticed last fall before I yanked the engine -- the FF sensor was losing readings. I fixed that this evening. My power to it was a crappy connection, but now things seem to be working more like normal.

So, since I want .85 lambda, I just take 1 lambda / .85 target lambda = 1.1765 EQ Ratio.

[DSteck]

You got it.