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E85 Tuning

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Do you have any direction regarding E85 Tuning? Given: The system I will be using to tune (ATR) references AFR as a measure of Lambda, so there are no compensations required for differences in Stoichiometric Mixtures, i.e. a reference value (14.7-1, 9.7-1 ...etc...). There is a Injector Variance Value that is adjusted specific to the Base Fuel Flow required, kind of like Link's G4+ uses and is variable depending on the fuel type being used. I'm assuming is it used to set a Base Fuel Flow and this Value is referenced as a "minimum" to which the rest of the fuel tables set their fuel flow accordingly, depending on the selected fuel's characteristics. I'm not sure how the Injector Variance is Scaled, without performing a "Trial by error" run to determine this. I'm just trying to understand the system right now, not actually tune. I have learned that because of the systems (EJ257 and Stock 2015 STI ECU) inability to properly adjust fuel trims accordingly, based on the combustion characteristics of E85 and the Stock NBO2 Sensors installed that are used for Closed Loop Fuel Control only, I will have to actually adjust the MAF Curve of the Engine to obtain the desired results. Have you ever encountered a situation where the MAF or VE Tunes needed to be adjusted to "Trick" the engine into thinking that it was receiving more air so that in Closed Loop Operation it would provide the "correct" amount of fuel to achieve the desired Lambda? I could see with port injection, and an alcohol based fuel (better evaporative/cooling characteristics) that you could possibly encounter a denser charge of air that is actually entering the cylinder, than what was measured and calculated by the MAF/IAT Sensors. So you would have to Adjust the Curve to allow the ECU to reference a "Higher" Value so that you could control the Fuel Flow more precisely to achieve the desired Lambda. I'm kind of just thinking out loud, thanks for any input!

We will be releasing a Flex Fuel course in the coming months however this is based primarily around standalone ECUs. If you are tuning for E85 on a factory ECU the problem is that usually there is no option to modify the fuel characteristics in the stock ECU code. This is essential to tell the ECU what the stoichiometric AFR of the fuel is and goes a large way to correcting the fuel delivery given that the engine will need around 35-40% more fuel on E85 than on gasoline.

Two ways of 'tricking' the factory ECU to provide this extra fuel are to either modify the MAF calibration to make the ECU see more airflow than the engine actually has, or alternatively reduce the injector scaling to tell the ECU the fitted injectors are smaller than they really are. Neither is a very neat solution in my opinion but often these are the problems we are stuck with if we are stuck with the OE platform.

Okay that makes sense. I just wanted to make sure I was understanding how the system operated properly. Sounds like I am on the right track. I know I'm kind of delving into it a little deep with the questions without the proper compensation for your knowledge. But thanks for humoring me. I'll continue my self studies in the meantime. Thanks again!

Hey Andre,

Since you're increasing fuel flow by approx. 30-40% would you then increase your MAF Curve Values proportionally with respect to your fuel flow requirements, i.e. increase your entire Curve 30-40%? I understand that with low flowing injectors you can stretch them to the limit "IDC" by demanding such a dramatic increase in fuel flow over stock injectors (which are not up to the task), and this could result in a lean condition. But what method for "compensating" for fuel change is preferable, with regards to using an OE set-up? Would you just have to find a happy median between increasing both your MAF Curve and adjusting your Injector Scale Value? Also the Injector Scale Value in ATR is a "value in microseconds of IPW that results in a stoichiometric AFR per Gram of Calculated Load", so wouldn't I want to increase (not decrease) this value to obtain a longer Duty Cycle to obtain the higher flow requirement of E85? Why would I want the ECU to believe the Injectors were smaller than they really are? Thanks for your time!