12P Flex Fuel Discussion

[TdracerTd]

I don't think it would have anything to do with wide band other than tuning it in the first place. The tune would need to look at differing ve table or correct ve setting at different load points based on a reading off the flex sensor. Well that's my take on it. It would need to adjust spark as well to be effective. Stoic is stoic when it comes to the output of a wideband. Fuel type does not matter.

[Dylan]

Only time wideband is used for fuel calcs is if you are using wideband ve learn. Otherwise it's all off the ve table. Flex fuel would alter the target afr. You would have set a 0% ethanol table and a 100% table and the flex sensors output would tell the ecu how far to swing between the 2. Wideband wouldn't come into that.

[vlad01]

Another usful modifier table on top of that is ignition offset depending on % mixture. less ethanol would want less timing in high comp engines or slightly more for low comp. You'd need to add that to boost as well.

[Dylan]

Could probably do that too with the mapa and b spark tables sensor voltage tells the ecu how far esch way to swing.

[vlad01]

yeah that would be sweet to have full functioning flex fuel 808s. Point is probably moot on my future e85 engine design as the comp is over 14 and very unlikely to withstand petrol lol

[Holden202T]

as i understand it, the flex fuel sensor provides a percentage for offsetting the AFR, ve table shouldn't need to change, spark is a nice one to be able to increase with more ethanol, but im not sure how easy that would be to apply compared to an AFR figure offset.

think of it this way, if you have a stock commodore v6 running 19lb injectors...... you want to put flex fuel setup and E85 into it, you need approx 35-40lb injectors, so you'd put them in and adjust the injector rate to accomodate.... once any tuning tweaks are applied and its all good on the bigger injectors with petrol, then if you changed all the AFR readings to read E85, in theory that should be all you need to do, to allow that setup to run on E85 .....

or you leave the AFR tables as petrol numbers and then add an alcohol percentage v's AFR offset table to the tune, populate accordingly, the flex fuel sensor then allows it to automatically monitor and adjust the ethanol content and adjust the target AFR to account for it.

[TdracerTd]

^^ That's what I was trying to say, but you put it so much more eloquently. The way I look at it is the VE tables are actually just means for adjusting pulse width at different load points. So flex would require a correction to the number at any specific load point proportional to the output of a flex sensor. Main point I was making is that a wideband or wide band functionality within $12P was not strictly a necessity for flex functionality. Nice to have but not strictly necessary.

[Dylan]

Flex sensor would nit alter the ve. Only the target afr.

[VL400]

I have split this topic and added some info to the second post for what this thread is about.

[TdracerTd]

I don't understand how changing commanded afr is going to work. At any given load point you're going to want pretty much the same commanded afr. Whether your looking at petrol afr or e85 or lambda, the output of the wideband sensor will be the same. To achieve "X" afr with e85 as opposed to petrol you simply need more fuel. Wouldn't you just need a multiplier like we do for boost?