commanding 13.21 instead of 14.68? Need some help please
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From: Knoxville,Tn
commanding 13.21 instead of 14.68? Need some help please Hey guys, Im having a little issue with my 07 avalanche. Ive tuned multiple gen 3 vehicles with my hp tuner and never had this issue but the Avvy is gen 4. Im sure its some kind of fuel adder table but I cant figure it out. Im trying to tune my fuel enrichment for 12.2ish so Ive got multipliers set at 1.20. Main table is right and says 14.68 But while logging Im showing that its commanding 13.21 instead of 14.68, so of course when it goes into enrichment its commanding 11.0 instead of 12.2. Any idea what could be causing this? it does it from a cold start and drive all the way to a warm drive....never changes. 
Thanks for any help.
Thanks for any help.
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Teching In
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From: Knoxville,Tn
That thought crossed my mind as well but it would have to be seeing over 25% alcohol to reduce the commanded that low and 25% is 13.25, not 13.21. And if that were the case, wouldn't it slightly change the ratio throughout driving? I guess I could just change my Stoich AFR tables to 14.68 all the way across to see if that changes anything? Is there a chance that the fuel Im getting has way more ethanol content then the 10% its suppossed to have or could the flex fuel sensor be bad?
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Even on pump gasoline with the ethanol added to it, you will command about 13.9-14.0, not even using what would be called a flexible fuel. 14.68 has never been commanded in my vehicles since about 2006. This 0.75 AFR difference really isn't that big?. Consider vehicles like my 98 which were not designed to run on E10, their stoich has been off that much, ever since ethanol has been added to fuel (they are set at 14.68 when the fuel they are burning is about 14). It really hasn't hurt these vehicles. Also consider that error has been to the lean side, which is worse than your problem to the rich side. Its very possible for the flex fuel sensor to be off a little, I don't know what accuracy is considered normal for these sensors? Since they are relatively cheap I doubt they are very accurate, but I don't think they need to be. It may not be bad, maybe they are only good to about +/- 10%? +/- 10% on ethanol content doesn't seem to be a problem with those older vehicles running E10 that were tuned for pure gasoline? Or there may be a little more ethanol in the fuel than what you think there is, but I would think this far less likely?
The ratio should only change if you add fuel to the tank, it should stay constant throughout driving. I'm not thinking you really have a problem here, just the numbers are not what you are hoping to see. Maybe if your ethanol sensor is reading off a little you compensate for it by commanding 1.15 under power enrichment?
The ratio should only change if you add fuel to the tank, it should stay constant throughout driving. I'm not thinking you really have a problem here, just the numbers are not what you are hoping to see. Maybe if your ethanol sensor is reading off a little you compensate for it by commanding 1.15 under power enrichment?
Last edited by ScottyBG; Feb 15, 2017 at 11:32 PM. Reason: spelling
I see it all the time. Lots of GM Virtual FF vehicles just get it wrong. Many get it right. I haven't found a reason for it. I had a 07 FF Yukon in front of me today commanding 13.1 on E10. LTFTs were -18%. I see a lot of them commanding 12.0-12.5 too on 100% gas. that would be 35%-45% ethanol. Only fix I've found is turning off flex fuel and telling them to run 100% or E10 but no E85.
Even on pump gasoline with the ethanol added to it, you will command about 13.9-14.0, not even using what would be called a flexible fuel. 14.68 has never been commanded in my vehicles since about 2006. This 0.75 AFR difference really isn't that big?. Consider vehicles like my 98 which were not designed to run on E10, their stoich has been off that much, ever since ethanol has been added to fuel (they are set at 14.68 when the fuel they are burning is about 14). It really hasn't hurt these vehicles. Also consider that error has been to the lean side, which is worse than your problem to the rich side. Its very possible for the flex fuel sensor to be off a little, I don't know what accuracy is considered normal for these sensors? Since they are relatively cheap I doubt they are very accurate, but I don't think they need to be. It may not be bad, maybe they are only good to about +/- 10%? +/- 10% on ethanol content doesn't seem to be a problem with those older vehicles running E10 that were tuned for pure gasoline? Or there may be a little more ethanol in the fuel than what you think there is, but I would think this far less likely?
The ratio should only change if you add fuel to the tank, it should stay constant throughout driving. I'm not thinking you really have a problem here, just the numbers are not what you are hoping to see. Maybe if your ethanol sensor is reading off a little you compensate for it by commanding 1.15 under power enrichment?
The ratio should only change if you add fuel to the tank, it should stay constant throughout driving. I'm not thinking you really have a problem here, just the numbers are not what you are hoping to see. Maybe if your ethanol sensor is reading off a little you compensate for it by commanding 1.15 under power enrichment?
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That thought crossed my mind as well but it would have to be seeing over 25% alcohol to reduce the commanded that low and 25% is 13.25, not 13.21. And if that were the case, wouldn't it slightly change the ratio throughout driving? I guess I could just change my Stoich AFR tables to 14.68 all the way across to see if that changes anything? Is there a chance that the fuel Im getting has way more ethanol content then the 10% its suppossed to have or could the flex fuel sensor be bad?
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Flex fuel sensors Many of the newer GM Flex Fuel vehicles have gone back to a flex fuel sensor so the 2014-2017 5.3L L83 flex fuel CK trucks (Silverado, Sierra, etc.) have a sensor, the 2011-2017 Caprice PPV has a sensor etc.
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Thanks for that information. All the ones I see getting it wrong are Virtual FF. I don't work on the 14+ trucks. I wonder if they went back to using a sensor because of that.
I see it all the time. Lots of GM Virtual FF vehicles just get it wrong. Many get it right. I haven't found a reason for it. I had a 07 FF Yukon in front of me today commanding 13.1 on E10. LTFTs were -18%. I see a lot of them commanding 12.0-12.5 too on 100% gas. that would be 35%-45% ethanol. Only fix I've found is turning off flex fuel and telling them to run 100% or E10 but no E85.
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Teching In
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From: Knoxville,Tn
OK so let me get this straight....if I disable flex fuel(which Im fine with), Then it should just default back to 14.68 Which is in the first slot of my Stoich table correct?
I dont run E85 and I would prefer to not be trying to hit a moving target while tuning.
I dont run E85 and I would prefer to not be trying to hit a moving target while tuning.
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stoichiometric AFR for current US pump fuel Keep in mind that most fuel in the US is now 10% to 12% ethanol so stoichiometric AFR is closer to 13.8 to 14.1. I know of one company that had fuel tested around the country as part of calibration verification for a durability application and the average stoichiometric AFR of the fuels they tested was around 13.9.
Most of the newer non-flexfuel GM vehicles have the table flat lined at 14.1:1 instead of 14.68.
Most of the newer non-flexfuel GM vehicles have the table flat lined at 14.1:1 instead of 14.68.
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Keep in mind that most fuel in the US is now 10% to 12% ethanol so stoichiometric AFR is closer to 13.8 to 14.1. I know of one company that had fuel tested around the country as part of calibration verification for a durability application and the average stoichiometric AFR of the fuels they tested was around 13.9.
Most of the newer non-flexfuel GM vehicles have the table flat lined at 14.1:1 instead of 14.68.
Most of the newer non-flexfuel GM vehicles have the table flat lined at 14.1:1 instead of 14.68.
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Target AFR for newer fuels 2014+ C7 Corvettes (LT1 & LT4), 2016+ Camaro SS, 2014+ 5.3 & 6.2 DI & 6.0L PFI CK trucks (except flex fuel), 2016+ CTS-V.
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Thread Starter
Teching In
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From: Knoxville,Tn
Well Im thinking about it this way...If I disable the flex fuel, get my AFRs and ignition right at 14.68 With PE around 12.5, Then turn flex fuel back on it will be commanding a richer mixture but will be correct and although Ill be leaving a bit on the table ignition wise, at least I shouldnt have to worry about KR since itll be cammanding a richer mixture based on alcohol content. This is my daily so Im not exactly trying to make power on the ragged edge.....just trying to bring those fuel trims down and maybe get a little more pep out of this 6500lb beast. 
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Virtual FF disable Yes, I believe the general consensus of the posts is either:
- Disable virtual FF and put a fixed flat-lined AFR level in the target AFR table (then our AFR comments in our prior post become important)
- Add a real flex fuel sensor
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