Results 1 to 18 of 18

Thread: stoichometric and VE table

  1. #1
    Tuner
    Join Date
    Jan 2021
    Location
    Cape Town
    Posts
    84

    stoichometric and VE table

    If the stoich figure for part throttle of say 14.2 be changed to 14.8, would this result in a number of LTFT data log cells showing lean numbers?

    If the relevant cells of the VE table then be increased in the tune, should that take care of the lean data log cells?
    2010 Jeep GC 5.7 Eagle Head motor, 2" OME lift, cats removed, full MDS delete

  2. #2
    Senior Tuner Ben Charles's Avatar
    Join Date
    Aug 2009
    Location
    Calibrating
    Posts
    3,371
    Stoich needs to be set for the fuel you have... it’s just a multiplier anyways.. going leaner on stoich leans out the base fueling with VE

    Email Tunes, [email protected]
    96 TA Blown/Stroked, 4L80E/Fab 9
    15 C7 A8 H/C 2.3 Blower/PI
    14 Gen 5 Viper
    Custom Mid Engine chassis, AKA GalBen C

  3. #3
    Tuner
    Join Date
    Jan 2021
    Location
    Cape Town
    Posts
    84
    Thanks Ben.
    2010 Jeep GC 5.7 Eagle Head motor, 2" OME lift, cats removed, full MDS delete

  4. #4
    Tuner
    Join Date
    Jan 2021
    Location
    Cape Town
    Posts
    84
    I tend to get a leaner LTFT for bank 2, even though having slightly increased the values of the lean cells for bank 2 in the bank 2 VE table.
    So, taking a shotgun approach, lowering the stoich for the even numbered cylinders (which can be done in the tune) should take care of the lean condition for bank 2, without having to manipulate the VE table cells.
    Am I correct?
    2010 Jeep GC 5.7 Eagle Head motor, 2" OME lift, cats removed, full MDS delete

  5. #5
    If the stoich figure for part throttle of say 14.2 be changed to 14.8, would this result in a number of LTFT data log cells showing lean numbers?
    In theory this should show rich STFT's and LTFT's... If you lean out the stoich, in an ideal tune, the ECM would subtract fuel, showing negative stft's...

    Unless I misunderstand how that table works?

    Curious,

    Thanks in advance

  6. #6
    Tuner
    Join Date
    Jan 2021
    Location
    Cape Town
    Posts
    84
    Raceghost, thanks for your reply. I follow your reasoning, but as you ask, how does the VE table values come into play, if at all?
    2010 Jeep GC 5.7 Eagle Head motor, 2" OME lift, cats removed, full MDS delete

  7. #7
    Quote Originally Posted by skala308 View Post
    Raceghost, thanks for your reply. I follow your reasoning, but as you ask, how does the VE table values come into play, if at all?
    If I understand correctly. The numbers within the VE tables are actually pulse width adders to the injectors. They are in decimal format. As I was looking at my tables for a 2007 SRT8 and reading up about the PE tables and how everything is calculated.

    I could completely wrong too, lol. New to speed density. Give me load based, and MAF based, and we are golden.

  8. #8
    Tuner
    Join Date
    Jan 2021
    Location
    Cape Town
    Posts
    84
    Raceghost, as I understand, the VE tables act as the basis from which the A/F mixture is adjusted based on the O2 sensor readings. So if the logged cell readings for LTFT read + then I understand that the VE value for the cell must be increased to give more fuel and change the logged reading from + to - or 0.

    So, then changing the tune set stoich value from say 14.5 to 14.8 should make the A/F mixture leaner. Now by not adding to the VE value in the tune, will the logged LTFT readings change from + to 0 or -, that is my question.

    Otherwise, dont change the set stoich value and simply adjust the VE values for the cells reading high + and high -.

    I hope some more knowledgeable tuner will clarify this for us.
    2010 Jeep GC 5.7 Eagle Head motor, 2" OME lift, cats removed, full MDS delete

  9. #9
    Advanced Tuner
    Join Date
    May 2006
    Location
    Waterbury CT.
    Posts
    293
    There is a lot of mystery on this subject as to how the OE handle the Stoich value and or what effect it has on the tune.

    A couple things to consider, if you have left to right bank discrepancy you need to look at sensors, vacuum leaks, exhaust leaks and ring seal, and ignition efficiency, NOT the TUNE.

    Never try and fix mechanical issues with tuning.

    Narrow Band O2 sensors only know 1 thing, Stoich, or Lambda 1.0 no matter the fuel type.

    Stoich values are effected by chemical make up of fuel.

    Gasoline through 100% ethanol looks like this.

    Stoich table..jpg

    No Matter the Stoich Value it still always Equal Lambda 1.0

    Narrow band sensors are only accurate at Lambda 1

    computer is looking for Lambda 1.0 if it sees 1.1 it adds 10% if it sees Lambda .9 it takes away 10% and so the LTFT learn this.

    Chrysler does it backwards Fuel To Air ratio rather than Air to Fuel ratio that most are used to seeing.

    Either way this value entered in the tune should match the fuel you are running.

    Most pump gas across America is 10% Ethanol or 14.10 AFR.

    Let me know if this helps.

  10. #10
    Quote Originally Posted by JANNETTYRACING View Post
    There is a lot of mystery on this subject as to how the OE handle the Stoich value and or what effect it has on the tune.

    A couple things to consider, if you have left to right bank discrepancy you need to look at sensors, vacuum leaks, exhaust leaks and ring seal, and ignition efficiency, NOT the TUNE.

    Never try and fix mechanical issues with tuning.

    Narrow Band O2 sensors only know 1 thing, Stoich, or Lambda 1.0 no matter the fuel type.

    Stoich values are effected by chemical make up of fuel.

    Gasoline through 100% ethanol looks like this.

    Stoich table..jpg

    No Matter the Stoich Value it still always Equal Lambda 1.0

    Narrow band sensors are only accurate at Lambda 1

    computer is looking for Lambda 1.0 if it sees 1.1 it adds 10% if it sees Lambda .9 it takes away 10% and so the LTFT learn this.

    Chrysler does it backwards Fuel To Air ratio rather than Air to Fuel ratio that most are used to seeing.

    Either way this value entered in the tune should match the fuel you are running.

    Most pump gas across America is 10% Ethanol or 14.10 AFR.

    Let me know if this helps.
    Just wondering if it is always the case that the banks will have the same ve unless there is a mechanical issue? With mine i always had one bank read differently to the other. Changed 02 sensors, injectors, plugs, swapped coils, borescope'd engine , vac and smoke tested but couldn't find anything to explain the discrepancy.

  11. #11
    So this brings up an interesting question. Since most fuel is 10% ethanol, and stoich is 14.10:1 then what is best gas mileage tuning at these days considering this. In Gasoline, we find best gas mileage at around 15.1:1 ~ 15.3:1... So should I be targeting different AFR's using my AFR gauge in AFR's vs lambda of a little bit richer than this? Like 14.5~147?

  12. #12
    Tuner
    Join Date
    Jan 2021
    Location
    Cape Town
    Posts
    84
    As per factory tune, bank 1 VE differs slightly from bank 2, not only for my Jeep, but other Chrysler/Dodge factory tunes also. So, no mechanical issues. Also Jeep runs, idles, accelerates super smooth and instantly. But thanks for comments JANNETTYRACING, much appreciated.
    Factory F/A for my Jeep and others = 0.0688 = 14.53


    So, my question still is, if I change 14.53 say to 14.7 how should the logged LTFT readings change, if at all?
    Last edited by skala308; 05-23-2021 at 08:23 AM.
    2010 Jeep GC 5.7 Eagle Head motor, 2" OME lift, cats removed, full MDS delete

  13. #13
    Advanced Tuner
    Join Date
    May 2006
    Location
    Waterbury CT.
    Posts
    293
    Quote Originally Posted by raceghost View Post
    So this brings up an interesting question. Since most fuel is 10% ethanol, and stoich is 14.10:1 then what is best gas mileage tuning at these days considering this. In Gasoline, we find best gas mileage at around 15.1:1 ~ 15.3:1... So should I be targeting different AFR's using my AFR gauge in AFR's vs lambda of a little bit richer than this? Like 14.5~147?
    Hard to say what values works best here is why.

    You have to forget AFR ratio and use Lambda.

    Again the Narrow band sensors are only accurate at Lambda 1 and that is what the computers will try and achieve regardless of the fuel type.

    Having the Stoich value match fuel used makes the math work and minimizes fuel trimming.

    Talking and using AFR is just plain confusing unless you are working with pure gasoline, then you can say 14.7 is target or 15.1 is optimum MPG. etc.

    Go back and look at the chart I posted, you can see AFR changes but all Equal Lambda 1.

    maybe you need to target 1.01 or 1.02 but don't know how you would force the computer to do that?

    Maybe Just Maybe this is how Chrysler uses Stoich?

    We can only assume how the OEMs use the Stoich ratio, either to target or to offset from Lambda 1

    Maybe someone smarter than me can chime in with some hardcore facts.

    I have seen that GM Ford and Chrysler all handle it differently to some extent.

    Ford uses Wide bands starting somewhere around 2011, instead of narrow bands which changes how they use the Stoich value also.

    On most cars I have been successful tuning on gasoline E10 14.10 Stoich then changing to MS109 with only changing the Stoich value to 13.40, and maintaining same LTFT and WOT Lambda.

    Also working with Flex fuel sensors and E-fuels, automatically reads E content and populates the Stoich value via the table above.

  14. #14
    Advanced Tuner
    Join Date
    May 2006
    Location
    Waterbury CT.
    Posts
    293
    Maybe you should test this and report be good content.

    I don't think it is the right way as it will move your further from E10 stoich value of 14.10

    Remembering Narrow bands are going to target Lambda 1

  15. #15
    Hard to say what values works best here is why.

    You have to forget AFR ratio and use Lambda.

    Again the Narrow band sensors are only accurate at Lambda 1 and that is what the computers will try and achieve regardless of the fuel type.

    Having the Stoich value match fuel used makes the math work and minimizes fuel trimming.

    Talking and using AFR is just plain confusing unless you are working with pure gasoline, then you can say 14.7 is target or 15.1 is optimum MPG. etc.

    Go back and look at the chart I posted, you can see AFR changes but all Equal Lambda 1.

    maybe you need to target 1.01 or 1.02 but don't know how you would force the computer to do that?

    Maybe Just Maybe this is how Chrysler uses Stoich?

    We can only assume how the OEMs use the Stoich ratio, either to target or to offset from Lambda 1

    Maybe someone smarter than me can chime in with some hardcore facts.

    I have seen that GM Ford and Chrysler all handle it differently to some extent.

    Ford uses Wide bands starting somewhere around 2011, instead of narrow bands which changes how they use the Stoich value also.

    On most cars I have been successful tuning on gasoline E10 14.10 Stoich then changing to MS109 with only changing the Stoich value to 13.40, and maintaining same LTFT and WOT Lambda.

    Also working with Flex fuel sensors and E-fuels, automatically reads E content and populates the Stoich value via the table above.
    I'm using widebands permanetly in my car, in addition to the factory narrow bands. So I see AFR's as one of my gauges, that is why I ask.

    Does this change your respons any?

    Thanks in advance

  16. #16
    Advanced Tuner
    Join Date
    Nov 2019
    Posts
    227
    Quote Originally Posted by skala308 View Post
    So, my question still is, if I change 14.53 say to 14.7 how should the logged LTFT readings change, if at all?
    In a pure speed density model, the calculated fuel mass for a given VE cell will drop by 14.53/14.7 ~1.2%. Thus the LTFT would increase by ~1.2% to compensate.

    Remember that in closed loop, the narrow band sensors will always target Lambda 1 or stoich of the fuel type in use. Therefore, altering the stoich F/A will not actually change the AFR you measure under closed loop conditions, it will just skew the fuel mass calculation and the trims to compensate.
    It will however change the measured AFR in open loop conditions by the percentage difference as given in the above example, as there is no feedback in OL for corrections to be made.

  17. #17
    Advanced Tuner
    Join Date
    May 2006
    Location
    Waterbury CT.
    Posts
    293
    Quote Originally Posted by raceghost View Post
    I'm using widebands permanetly in my car, in addition to the factory narrow bands. So I see AFR's as one of my gauges, that is why I ask.

    Does this change your respons any?

    Thanks in advance
    NO but I would recommend set your gauges to read out in Lambda.

  18. #18
    Tuner
    Join Date
    Jan 2021
    Location
    Cape Town
    Posts
    84
    WOW, guys, thanks for your shared knowledge; I still have much to learn and understand.
    The Ethanol % mixture in our fuel was something I never paid attention to, since I am not a racing driver. In South Africa where I am, our fuel contains from 8% to 10% Ethanol. How does that get dialled into the Chrysler/Jeep tune? Under Spark>Advance is a box for "Base Alcohol" with 0.00 in the tables.

    I experimented today by driving the same route and manner with the following results. I do not have wideband sensors.
    1. From the logged LTFT+STFT data, reduced the lean cell values by 10% in the VE tables. This resulted in an increased lean value logged data reading for the cells (larger + values)
    2. Changed the tune stoich values from 0.0688 to 0.0704. Now I expected all the logged data to show richer readings. Meaning the + logged values will reduce and the - logged values will increase. That then also was the result.

    Also as I already know, with normal cruising through the gears, there will be + red cells logged in the fuel trims (particularly STFT) in the upper log cells, due to deceleration fuelling where there is no fuel supplied.

    So, I deduct that to have less + values in the log and more 0 values, this could be achieved by adjusting the values in the VE tables.
    2010 Jeep GC 5.7 Eagle Head motor, 2" OME lift, cats removed, full MDS delete