Printable View
When I dialed my MAF in at 80% E, EQ error was +/- .5%. Now I'm back down to regular 93, showing 11% E, and the EQ error is around -4%. Pulled the stoich table values from a factory flex truck tune, 14.678 at 0% interpolated to 8.976. Is that table just that far off, or is there something I'm missing?
I think it's pretty accurate, never really had reason to correct it before. Are we talking the ~4% with just normal driving in or at WOT?
WOT specifically, although at a glance it looks like LTFT's are around -4% more throughout the log as well compared to my last E85 log
You are not taking into account the engine's ability to combust e80. All of these engines were built to run gas. Not near enough cylinder head pressure for efficient combustion of ethanol/alcohol. So you end up rich when burning gas.
Wouldn't it actually be that all the excess ethanol that isn't combusting make the resulting mixer read rich in the wideband, while a complete burn of gasoline would make it read leaner...?Quote:
Originally Posted by jsllc
The math for ethanol is 100% There is no miscalc on that unless it is changed from defaults.
Using your theory lambda 1 would be richer.
An incomplete burn will show more free O2 for the WB to pickup so measure a higher lamba. You will and fuel to drive that down. A more complete burn will show less free O2 therefore lower lambda and you will reduce fuel to bring the number up.
WB is an O2 sensor not a fuel burn sensor.
Just meant a more complete burn of the fuel would result in a leaner reading due to less unburnt fuel remaining after combustion. But okay. So you're saying to just play with PE tables to get to my desired lambda even if the MAF table will be off? i.e. tell it to target ~.91 to get .87 actual?
Try setting your Injector Flow Rate Alcohol Multiplier to 1.0 for all and tweaking your MAF again to be inline. Then go back to E85 and see if there is less variance in LTFT's between fuels.
More complete burn means lower lambda. Less free O2.
No you do not change PE. You change Ethanol modifiers.MAF is either right or not. Usually you tune with no Ethanol, then tune with it getting the modifiers right with no change to MAF.
I'll give that a shot. The fact that the 75% cell was 3% and the 87.5% was around 3.5% is promisingQuote:
Originally Posted by TriPinTaZ
any update on changing the multiplier to 1?
No sorry, damn tank of 93 just won't finish lol. I'll be filling up in a day or two with E again, got my MAF to around -.5% +/- .5% right now, I do a few pulls every day on the way home and multiply by half % to make the change slower and more precise. Hoping 6000-8500hz is all within .25% by the time I switch back over. Haven't bothered to do a full MAF tune since I have a set of cat deletes and a mamo tb to throw on when I get the chance, next step will be a cam after that so ill actually do a full airflow tune since that isn't happening for a year or soQuote:
Originally Posted by str8dum1
So, filled up with E today. Tank is sitting at 75%. EQ error is still within .5% for the most part, so I'd say that changing that multiplier did the trick, thanks TriPinTaZ
Why is that multiplier setup for not 1.0 to begin with? What are they trying to compensate for?
Quote:
Originally Posted by BDPhoto519
It is adding fuel volume. It could just be that GM didn't finish the tables for these cars since they are not Flex Fuel from the factory. Or GM could have some other reason. We will never know.
I find myself making tweaks to the stoich table.. Only way to correct for a lean condition as alcohol content changes.
You would think a by the book chemistry defined stoich table would be the way to go but it can be 7-10% consistently off part throttle and wide open.
Do you mean as content changes as in the first 5 min of driving after switching from pump gas to ethanol? Cause im sure thats gotta be normal as the fuel content is rapidly changingQuote:
Originally Posted by Alvin
When flex-fuel is setup correctly there are none of these issues and stoich matches the chemistry formulas just like it does in a calibration from the factory. Only when the tune is wrong do these things happen.Quote:
Originally Posted by Alvin
So it looks like the consensus here is to change the Alcohol Injector Flow Multiplier back to 1.0 stock? I am currently copied the values from a GENV 5.3 flex fuel truck, I would think this would be best because we know for a fact GM programmed this table to work with alcohol because yes some of the other LT1 tables for alcohol look like they were just forgotten or just random stuff was put in there, but you would think this would be a liability for GM though to do that kind of stuff?
So why then does some factory calibrations not follow the chemistry? There's more to it than just balancing the equation. Like combustion efficiency for one!Quote:
Originally Posted by jsllc
As someone who tunes a ton of cars I'm telling you it doesn't always work out.