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Thread: What's going on with commanded air fuel in logs?

  1. #1

    What's going on with commanded air fuel in logs?

    I just was review my logs and commanded air fuel ratio doesn't represent my true commanded. The wideband shows correctly, and it's going into PE, but it's not displaying in my logs. It's staying at stoich.

    Never had this problem until the update to the latest version.

    Also, RTT doesn't do anything for PE.

    2004 Z06 Corvette.

  2. #2
    My stoich is 12.082

    My PE is set to 0.96582

    Scanner should read 11.66

    Its reading 12.082

    Please advise.

  3. #3
    I meant commanded should read 12.52.

  4. #4
    Tuning Addict 5FDP's Avatar
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    Did you type that out right?

    The power enrichment EQ ratio needs numbers larger than 1.000 to make the mixture richer. So if you wanted 11.66 commanded AFR with a stoich value of 12.082 you need to use the number 1.036.

    12.082/1.036 = 11.66.

    I'm puzzled as to why you'd use a number so small because if that was using the gas scale of 14.68, that's still commanding 14.1 AFR under PE and that's super lean.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  5. #5
    I'll try to explain.

    Stoich is for an e85 mix.

    I'm trying to command leaner.

    12.082/0.9625 = 12.55

    Commanded AFR is stuck at 12.082. Commanded should show 12.55 on the scanner.

    In all cases, does PE need to be higher than 1.00?

  6. #6
    Tuning Addict 5FDP's Avatar
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    Yes, in all cases it must be higher than one.

    You need to stop thinking in AFR when using E85 mix, use lambda and it will always be right.

    1.00 lambda will be the same for 93 octane and E85.

    The EQ ratio is using the gas scale and if you want to command .85 lambda you could use that to see the AFR side.

    14.68 X .85 = 12.47

    14.68/1.178 = 12.46.

    Then if you want to command 12.55 it should be 14.68/1.169 = 12.55.

    You can also do 14.68/12.55 = 1.169, which you'd input into the EQ ratio.
    Last edited by 5FDP; 07-24-2019 at 04:50 PM.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  7. #7
    Quote Originally Posted by 5FDP View Post
    Yes, in all cases it must be higher than one.

    You need to stop thinking in AFR when using E85 mix, use lambda and it will always be right.

    1.00 lambda will be the same for 93 octane and E85.

    The EQ ratio is using the gas scale and if you want to command .85 lambda you could use that to see the AFR side.

    14.68 X .85 = 12.47

    14.68/1.178 = 12.46.

    Then if you want to command 12.55 it should be 14.68/1.169 = 12.55.

    You can also do 14.68/12.55 = 1.169, which you'd input into the EQ ratio.
    Stoich is 12.082 for my e85 mix. This is what I need it at.

    So are you saying that if I wanted to command 12.55, with my current stoich, which us 12.082(I know it's not lambda, and I know it's not truly gas AFR, that's not what I'm after), I need to change my stoich to 14.68, which is gas stoich? That doesn't make sense.

    I'm looking to get commanded EQ to read right on the scanner, so that it reflects my PE.

    12.082 / 0.9625 = 12.55. This is what I should be seeing.

    If you're saying that PE has to be 1.00 or greater, then how can I command 12.55 with a stoich of 12.082?

  8. #8
    Tuning Addict 5FDP's Avatar
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    Cheese and rice man.

    Forget what your stoich value is, that doesn't mean shit anymore because it's a gas/E85 mix.

    The EQ ratio is based on a gas scale and if you want to continue thinking in a gas scale way of thinking to get a desired commanded AFR value then you need to use 14.68 as the first value. The physical stoich value you are running does not have to change, just the value you are using to get your number does.

    I'm serious here, just change the damn EQ ratio commanded value to 1.169 and the computer is going to spit out 12.55 commanded AFR under power enrichment. It can't get much simpler than that.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  9. #9
    Tuning Addict 5FDP's Avatar
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    Even this crude example will show you this.

    Look at the 12.5 commanded AFR value and what EQ ratio you must command to get that value is.

    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  10. #10
    This is helpful...and I think I get it. I am going to stare at this for a while.

  11. #11
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    so the question remains unanswered, can you command leaner than stoich AFR with PE?

    If not thru PE, then how?

  12. #12
    Tuning Addict 5FDP's Avatar
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    Not through PE.

    If you wanted to command or "run" leaner than stoich you'd have to go to an open loop only setup. So toss the o2 sensors in the garbage and disabled all fuel trims and closed loop functions. All tuning will be done solely with a wideband o2 sensor and you'd be fudging the MAF/VE or just the VE to run leaner than the stoich ratio by removing fuel from those area's of the table.

    For most people this is not ideal because they want closed loop fuel control and they don't need to drag the laptop around with them all the time.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  13. #13
    So if I'm running E43, and my AFR guage only reads12.50 in AFR, it's really 10.35, correct?

    I wish my guage read in lambda.

  14. #14
    Tuning Addict 5FDP's Avatar
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    I guess I don't think of it that way.

    It's still 12.50 because your wideband uses the gas scale in this case. If your widebands stoich was 12.18 like the chart above says, then it would show 10.35 on the gauge for .85 lambda.

    If the wideband won't read in lambda just don't change your way of thinking for AFR, just keep your mind at 14.68 being stoich. That way 12.5 afr is is still 12.5 afr on the gas scale.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  15. #15
    Gotcha.

    To hit lambda of 0.85 on E43, my guage needs to read 12.5.