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Efi & e10

3450 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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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?
You can adjust idle, cruise and WOT A/F targets on the EZ EFI by changing the A/F targets for those conditions. As I said, I am just learning, but it seems that since they have the base tune set for E0, an adjustment for E10 would be in order?
Right. I will tinker a little but based on E0. The article includes settings for E85,(they are richer) but I omitted them from my post for brevity.

Just engaging in a little 'mental masturbation'! It helps me understand the system better when I learn about things like this.
I understand the concept of the lambda # and that a wideband converts it to an A/F #.
But if the computer thinks you are running E0 isn't it converting from a base of 14.7/1 ?
It doesn't know it is seeing E10, and change the basis of the calculation, so you would need to adjust the target to compensate, right? What you are saying seems counter - intuitive. I mean, you can't calculate a correct ratio for one fuel when using the numbers for a different fuel?
(remember, I am just trying to learn, not argue!)
OK - I think I got it...the O2 sensor reading reflects residual O2 or unburned hydrocarbons with ideal being lambda 1, regardless of the fuel. It just converts that to the more familiar (and more confusing) E0 number. I was going the other way and thought it was calculating lambda based on the fuel.
Thanks a lot for your patience!
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