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Efi & e10

3449 Views 14 Replies 4 Participants Last post by  zwede
Ran across an article in the July/13 Hot Rod mag (pp 140-44) re: tuning EFI for E10 or E85. Being new to EFI (FAST EZ EFI just up and running) this was something I hadn't heard about before. I did a search of this forum but didn't turn anything up, so I thought I would put this out FYI and for comments.

HRM has a table showing adjusted A/F ratios for pure gas, E10 and E85. The also give a formula for converting one target A/F to a different fuel. In general they say to fatten up the target A/F for fuels with ethanol (no surprise, but I just assumed the computer already would do that).

pure gasoline stoichiometric 14.7
" " max power rich 12.5
" " " " lean 13.23

E10 stoichiometric 14.08
" max power rich 12
" " " lean 12.70

I can't get anything but E10 unless I buy race gas (not happening!) so I guess I will change my A/F targets somewhat.
What are you all doing, if anything?
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Don't change your target AFR!

You have a lambda sensor, it can't measure AFR (yes, even a wideband still only measures lambda). Stoich is always lambda 1, regardless of fuel. The wideband controller multiplies the lambda by 14.7 and shows you the number because we know what AFR is, but most of us don't know lambda.

E0, E10 or E85, stoich is still lambda 1. But it is presented to you as 14.7:1.

If you go from E0 to E10 or E85 you will have to richen the fuel map (inject more fuel), but your target AFR will stay the same since it is really a target lambda.
Isn't it a federal mandate that all commercial gasoline be E10 now? Initially there would have been some variation as E 10 was mixed into station tanks, but by now I would think it would be pretty consistent?
I believe it is only federally mandated in counties that do not comply with some air quality standard? Once you get out in the rural areas you can still get straight gasoline. At least that was the case a few years ago.
Yeah but doesnt the ez efi stuff self tune based on your air fuel ratio input table? I am not familiar with ez efi but if you setup the self tune table to target 12.8 to 1 for wot but dont tell it the fuel is E10, or E85 then its gonna look at 12.8/14.7 which is lambda .87 which is fine for gas but not fine for E85.
Lambda 0.87 is a good WOT mixture no matter what fuel. As long as the EZ-EFI converts lambda to AFR assuming straight gasoline, you will put 12.8 into the WOT target AFR. If you're on E85 then you won't actually be running 12.8:1, it will be way fatter. But if you look at the EFI readouts, the target will be 12.8:1 and it will read 12.8:1 from the lambda sensor.

All this is if the EZ-EFI doesn't have a way to change the lambda->AFR constant (I don't know if it can, I haven't used it).

All this confusion comes from that the wideband manufacturers thought we were too dumb to grasp lambda. :(
Let's say you want to run stoich. The EFI is setup to show stoich as 14.7:1 (E0). So you enter a target of 14.7:1. This is lambda 1.

Now you fill up with E10 where stoich is 14.1:1. You still want to run lambda 1. If the EFI knew you used E10 it would show lambda 1 as 14.1:1. But since it doesn't know it will show lambda 1 as 14.7:1. Therefore your target is still 14.7:1. The EFI will see lambda 1 from the O2 sensor and show it to you as 14.7:1, even though in reality you're running 14.1:1.
Yep, that's it. Life would have been so much easier if they had just always shown us the lambda number and not a calculated AFR. But back when everything was E0 it must have seemed like a good idea.
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