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Thread: Question about LTFT

  1. #11
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    Default Question about LTFT

    You can log MAF airflow and see what it is doing.

    You can also check the wing by measuring voltage at the MAF connector. Should have 5 volts on the yellow signal wire, ground to battery and positive to signal wire.
    Last edited by LastCall; October 3rd, 2016 at 12:07 PM.
    00 Silverado Z71, LQ9 w/ LS3 heads, BTR cam, Whipple 2.9@8#, 4l80E

  2. #12
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    I ran a quick log to check the airflow. I never got to 275. I guess I need a new MAF. Any recommendation or just go with OEM? This truck is used as to tow an enclosed trailer with Motorcycles.

    LS1B_0198.efi
    2003 Chevrolet Silverado 2500HD 6.0L Automatic 4 X 4

  3. #13
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    This might seem like an odd question... but have you made any attempt to tune that thing at all? Also, have you done anything silly like de-screen the MAF?

  4. #14
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    As far as I am concerned, more information is better so keep the question coming. The only adjustments I have made were to the Transmission and Speedometer. The MAF as far as I know is OEM (with the screen). I cleaned it at the time I replaced the motor. The truck has about 225,000 on it. I replaced the motor at about 200,00 with a GM motor. I replaced the crank and cam sensors with new from GM at the time of the engine replacement. I installed a new Delphi fuel pump and Napa FPR at about 150-175,000. A new Fram Air Filter and Autolite spark plugs were replaced about 5,000 miles ago. The Oil Pressure switch was just replaced by GM about 1500 miles ago (who knew if this goes bad it will take the complete engine down).
    2003 Chevrolet Silverado 2500HD 6.0L Automatic 4 X 4

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    2003 Chevrolet Silverado 2500HD 6.0L Automatic 4 X 4

  6. #16
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by Dirktdolman View Post
    I ran a quick log to check the airflow. I never got to 275. I guess I need a new MAF. Any recommendation or just go with OEM? This truck is used as to tow an enclosed trailer with Motorcycles.

    LS1B_0198.efi
    At 5800 rpm at WOT your MAF under-reports (205-225 g/s)...

    you can see in attached pic that MAF g/s barely rises as rpm sweeps up:

    Click image for larger version. 

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    this causes reduced fueling (since fueling is proportional to airmass)...

    meanwhile trims generally go positive to to maintain stoich in CL.

  7. #17
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    Thanks Joe I will pick up a OEM MAF tomorrow morning and run a couple more logs.

    I tried to do a CASE learn but kept getting an error. It would never get to 4000 before doing the hiccup.

    Click image for larger version. 

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    2003 Chevrolet Silverado 2500HD 6.0L Automatic 4 X 4

  8. #18
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by Dirktdolman View Post
    ...

    I tried to do a CASE learn but kept getting an error. It would never get to 4000 before doing the hiccup.

    Click image for larger version. 

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    Are you opening the throttle to bring rpm up (to get over 4000)...?

  9. #19
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    Yes, not sure how do get the RPMs up without opening the throttle.

    First warm up engine to operating temp...

    then with vehicle parked and engine running at idle:
    - connect scantool (click green connect button),
    - goto DVT tab,
    - select controller,
    - click Activate,
    - goto Learning subtab,
    - click CASE Relearn (see next line),
    - open throttle to increase RPM above 4000, you must do this within 10 seconds (see next line),
    - when you get the stumble/misfire (it will be quite notcieable) immediately release throttle,
    - let engine spindown to idle,
    - after reaching idle, turn off engine and wait 20 seconds,
    - while waiting 20 seconds, you can click Deactivate.

    You may possibly have to have brake applied and/or parking brake applied during this.

    Only one CASE relearn can be done per ignition cycle
    2003 Chevrolet Silverado 2500HD 6.0L Automatic 4 X 4

  10. #20
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by Dirktdolman View Post
    ...

    I tried to do a CASE learn but kept getting an error. It would never get to 4000 before doing the hiccup.
    Are you saying that the stumble/hiccup would occur before 4000 rpm...?

    Does the scantool display an error...?

    Can you post the scantool log (do select all copy/paste from the text shown on the Console tab).

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