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Thread: high +LTFTs with MAF, and serious driveability with LTFTs disabled

  1. #1
    Potential Tuner
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    high +LTFTs with MAF, and serious driveability issues with LTFTs disabled

    Tuning a bone stock 99 Silverado extended cab long bed 2500 4x4 w/ 4L80E 6.0L LQ4 with stock iron heads, cam intake and exhaust. Only mod is LQ9 injectors. Here is what ive done:

    Running only 92-93 octane
    Disabled and removed EGR, disabled DTC's
    Fixed speedo for larger tire size - this modified various shift speed tables automatically
    Updated IFR table to that of LQ9 injectors installed
    removed TQ mgmt from engine and trans
    COT disabled
    updated PE to lean out the AFR (1.1293 EQ Ratio across the board = 13:1 AFR), and drop the PE Enable to more like that of my 01 T/A LS1 (30KPa PE MAP enable and 64% TPS at low RPM tapering to 26%)
    made a composite spark advance map of maximum values of all 99-06 LQ4, LQ9, & 01-02 F-body LS1
    copied high octane spark table to low octane spark table
    whenever I updated the high octane VE table, I copied that over to the low octane VE table


    I changed the DTC's on the MAF to fail it to SD mode, and unplugged the MAF. Since the IAT is located in the MAF, when I unplugged the MAF the IAT went to -38degF. Originally I was doing the VE tuning using the LTFT technique (no WB02 installed at this point), with the IAT reading -38degF, and I felt like I got it pretty good, but still had a hard time getting to -4 < LTFT < 0 on varying ambient condition days.

    Then I had the idea of updating the IAT calibration curve to fake it out to be the ambient temperature on that given day, so at some point I made the calibration =75degF across the board and re-tuned the VE using the LTFT. I got it pretty good again and the truck was running pretty good on the SD tune, just a few quirks like I wasn't getting the spark advance I thought I should be on the Advance vs Cyl Airmass vs RPM table, and the shifts were much harder than when the MAF was connected (just found out the Max Line Pressure increases and how to fix this). I had no knock retard going on and all the LTFT's were between -4 and 0.

    So I felt I had gotten the SD tune pretty good and went to plug the MAF back in, back out the MAF DTC settings, and set the IAT calibration back to stock. Now when logging I get super high LTFT's (+24 almost in every cell I hit), my spark advance is more in line with what is in the Advance vs Cyl Airmass vs RPM table, the shifting is back to a 'normal' stock feel (I have not modified any trans parameters other than TQ mgmt), and I'm getting Knock Retard in some higher cruise type RPMs and Cyl Airmass cells.

    I have been staying out of the PE range by limiting TPS to no more than 60%.

    I have not modified any of the Burst Knock or Knock Retard settings as I was going to use these stock conservative values to pull timing from the cells i'm getting knock via the Advance vs Cyl Airmass vs RPM table in 2deg increments until I don't see any more knock. Once I get the Advance curves dialed in, I would then reduce the conservatism in the Knock / Burst Knock parameters.

    Questions:
    1. Why are my LTFT's with the MAF installed tending to +24? Could my MAF be bad or just need to do the MAF portion of the tuning? I've had a cold stumble after startup driveaway for a couple years, which precipitated me getting HP Tuners. Its almost like the PCM has to 'learn' to compensate for the MAF or something else. It doesn't always do it, and as far as I can tell it doesn't matter if it's hot outside, or cold, or to some degree if the engine is warmed up (either by idling in the driveway or by the block heater).

    2. Could the above condition be causing a lean condition that is causing the Knock Retard during Cruise throttle transitions? I don't want to be chasing what I think is too advanced timing if its a transient lean condition or just overconservative Burst Knock settings.

    Just tonite I followed this sticky to log the MAF Hz, and when I disabled the LTFT's, ran the truck getting on the highway (probably had warmed up enough to start using the LTFT's) it started to fall on its face and could not maintain any sort of highway speed. So I pulled over and reflashed my previous tune and the problem went away. Makes me think more and more that the LTFT's are masking a serious MAF 'soft' failure.

    http://www.hptuners.com/forum/showth...096#post121096

    I'm using EC_Tunes MAF!LTFT.cfg config and histograms. I'm brand new to looking at these histograms so I have little idea what they mean.

    Attachment 1 is the log where I lost power on the highway after disabling LTFTs per the above sticky
    Attachment 2 is the log after I reflashed my prior .hpt with LTFTs enabled and drove home without issue
    Attachment 3 is the .hpt with the LTFTs disabled
    Attachment 4 is the .hpt with the LTFTs enabled

    Thanks for all help!
    Last edited by Throttler; 04-20-2014 at 09:23 AM.

  2. #2
    Tuner in Training
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    Apr 2013
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    how does it run on stock tune but setup to run only on maf? i would think nearly a stock truck you shouldn't be too far off on maf cal so it might just be bad, but i would see how it runs on only maf with stock tune just to make sure its not your tune way off.

  3. #3
    Potential Tuner
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    Good point and actually yesterday I pulled one of my early logs before I had made any substantial edits to the tune and I was seeing the exact same thing, +24-25 LTFT's in all cells I hit. At the time when I had HPT for just a day or so I thought my VE table was way off from the factory, so started to disable the MAF and tune the VE table.

    Since I'm even more concerned that my MAF is off now, I've gone back and disabled it in the tune and after not seeing the SD tune for a week or so, my log this morning is right where it should be (I think).

    I also ordered a new MAF.

    In case anybody cares to see without downloading the log files, attached are 2 .jpgs showing the LTFT's and STFT's from the ~stock tune.
    Attached Images Attached Images
    Attached Files Attached Files

  4. #4
    Advanced Tuner JamesLinder's Avatar
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    YOUR VE tables are trashed. You would be better off using stock VEs than what you have. Timing looks considerably too high
    at the higher RPM's with low loads (top right of timing table). Again, stock timing would be better than what you're using.
    Make certain you are using the exact, correct, fuel injector values. Bottom line, do not waste your time tuning until you obtain
    a wide band oxygen sensor, and then hook it up to work properly with HP tuners scanner and then you can tune the motor
    correctly. Fuel trims will not work for tuning, period.

  5. #5
    Advanced Tuner JamesLinder's Avatar
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    If I did anything before getting a wide band sensor, I would increase the stock MAF curve by 7.5% across the board, increase
    the stock VE's by 7.5% from 2000 RPM up to 3600 RPM for all MAP values, then increase them 10% beginning at 4000 and
    beyond for all MAP values, and then decrease VEs for 1200 RPM and below by 15% for all MAP values. Go with a PE value
    of 1.15 across the board to stay on the safe side. This is plenty lean to yield good performance. If you should see positive
    fuel trims at WOT above 4000 PM, then increase the MAF table another 2.5% above 4000 RPM, otherwise stay with the
    7.5% increase across the board. If things go well, then post your NEW tune and I will look at your timing table to see
    what needs to be done - but for now go back with what would be stock timing for the motor.