Tuning for E85 using the stock O2 sensor?

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Bigfieroman
Posts: 21
Joined: Wed Mar 11, 2020 11:31 pm

Tuning for E85 using the stock O2 sensor?

Post by Bigfieroman »

Hello,

When I was tuning my supercharged 2007 S2000 on 93 octane over the last few years, it became evident that the stock O2 sensor pegs rich at 10.14 LAM or 11.52 LAM.ADJ; no matter how rich the car runs, that is the indication. That worked fine for gasoline, as I was generally targeting 11.8 LAM.ADJ on 93. However, I recently bought the parts necessary to run flex-fuel on the car (FFC-100 and a GM sensor, plus a big box of fuel system parts), and e85 will require a much richer target AFR than the stock O2 sensor can measure.

What would be the best approach to tuning this setup? Is there a way to replace the stock sensor with something that has more range? I know I can always buy a stand-alone wideband, but that data won't be integrated into the log files. Do I just tune it on gasoline and extrapolate fueling and timing through the range of ~E10-E85?

Thank you.
KTuner
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Joined: Mon Jul 22, 2013 8:13 pm

Re: Tuning for E85 using the stock O2 sensor?

Post by KTuner »

I think you're confused a bit here. If you want to target .8 lambda on gas and .8 lambda on ethanol the target AFR as displayed in the software, converted to gas (14.7), will not need to change. I think you're trying to look at AFR values after lambda has been converted for the different types of gas. Take a look at some online explanations of tuning with E85 and what lambda means as it is converted for different gas types. There are also tuning classes that can help you understand the differences. Coaching tuning practices is out of our realm of support.
Bigfieroman
Posts: 21
Joined: Wed Mar 11, 2020 11:31 pm

Re: Tuning for E85 using the stock O2 sensor?

Post by Bigfieroman »

I understand the difference between Lambda and AFR, but the logs that come out of KTuner (at least the version of the software that I was using last year) show AFR, not Lambda, even though the columns in question are LAM, LAM.ADJ, and LAM.CMD. The values in these columns in the datalogs are typical for AFR; ~14.7 at idle and I was tuning for ~11.8 WOT. As far as I can tell, the export logs from the program do not contain a true Lambda.

Obviously I can convert the AFR in the log to a true Lambda with a quick formula applied to the columns, but my original question would then apply, as the sensor can't read an AFR below 10.14, which is a lambda greater than 1 on e85.
KTuner
Site Admin
Posts: 3329
Joined: Mon Jul 22, 2013 8:13 pm

Re: Tuning for E85 using the stock O2 sensor?

Post by KTuner »

From what you just said you don't have a full understanding of how it converts. The previous post addressed the issue you think you have, which you really do not. The sensor reads in lambda. The sensor does not need to read AFRs below 10 when converted with a multiplier of 14.7 to display as gas to utilize or target ethanol properly. 10.14 AFR with 14.7 as the multiplier for gas is .69 lambda. I highly doubt (and fully hope) you're not trying to target lambdas lower than that, as that just doesn't make sense.

Feel free to convert that lambda to the fuel of your choice for reference by replacing 14.7 with your fuel's multiplier. Better yet there's a setting right in the preferences for gas type under wideband settings. If you had an understanding for the conversion you wouldn't need it, but it's there if you'd like to use it.

See previous post.
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