Does this tuning logic make sense ?

[eficalibrator]

Interesting that you say to change the stoich point in the tune.

Does GM (or whatever other factories) tune on E0? They are always a 14.7 or 14.6 it seems.

Why not calibrate them at 14.1 out of the factory since you can't really even get E0 anymore? Now E15 is approved as well. :-( :-( :-(

They are more worried about passing EPA emissions and fuel economy tests. For those tests, they use a specific fuel (Tier II RFG) which is a very specific, consistent blend with a stoich point really close to pure gasoline. Leaving the stoich point alone in the calibration means that these tests require almost zero learned correction to hit the desired lambda in open loop.

That said, the actual federal test procedure calls for a "prep cycle" where the ECM gets a chance to learn any necessary fuel trims over the same drive cycle. Ford has recently started skewing the stoich point in their calibrations to something closer to E10. In theory, it doesn't really screw up the EPA tests as long as a good fuel trim learn happens on the prep cycle. What this does is help make real world fueling a bit more precise as the customer fills up at some random gas station with an unknown blend.

I prefer to calibrate for the fuel that's actually in the tank when I'm looking at the car. I will often take a fuel sample in order to determine the alcohol percentage and stoich point. If I don't have an exact measurement, I still tend to SWAG it based on what I know about the available fuel in the area.

[Higgs Boson]

Good info.

There is so much back and forth over changing the stoich value in the tunes. I guess you should change it if you are using lambda but leave it if you are using AFR? Or change it to match your wideband if you are using AFR???

Better to just use lambda, I know. But some people just...don't....

[realcanuk]

Good info.

There is so much back and forth over changing the stoich value in the tunes. I guess you should change it if you are using lambda but leave it if you are using AFR? Or change it to match your wideband if you are using AFR???

Better to just use lambda, I know. But some people just...don't....

I think i understand that lambda is the better way in general but if you only work on one car, and your wideband is set to read the stoich value you use, (whatever that may be), then I dont really see the difference.

[Gh0st]

I hear you, but why does everyone say to change it for E10 ? Is it not worth doing ?

So that your numbers are right when you're commanding OL fueling. Commanding a PE of 1.175 with 14.67 set as your stoich won't put you in the lambda target you want for E10 or whatever fuel you use because you are pretending you're running pure gas.

[Higgs Boson]

So that your numbers are right when you're commanding OL fueling. Commanding a PE of 1.175 with 14.67 set as your stoich won't put you in the lambda target you want for E10 or whatever fuel you use because you are pretending you're running pure gas.

if you are using ltft's the fuel addition would carry into pe, right? I mean I agree it's not the optimum solution but also not the end of the world....

[Gh0st]

if you are using ltft's the fuel addition would carry into pe, right? I mean I agree it's not the optimum solution but also not the end of the world....

That doesn't mean your fueling will be right. If your MAF calibration is dead on during the hz spectrum of WOT load, then LTFT adding fuel would make you run rich and once again not in your lambda target

Your MAF calibration could also be incredibly wrong and then all the LTFT in the world won't save you...

[Higgs Boson]

That doesn't mean your fueling will be right. If your MAF calibration is dead on during the hz spectrum of WOT load, then LTFT adding fuel would make you run rich and once again not in your lambda target

Your MAF calibration could also be incredibly wrong and then all the LTFT in the world won't save you...

well yes if things are "incredibly wrong" then I don't think youd be all that worried about e10..... or maybe even know what e10 is.....