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Thread: What would cause LTFT bank 2 to be -100%?

  1. #1
    Tuner Joe_G's Avatar
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    What would cause LTFT bank 2 to be -100%?

    Scanned a buddy's 98 C5 last night and his bank 2 LTFT was -100% across the board and not changing, bank 1 was normal, -3% or so, something reasonable. I cleared the LTFT's via VCM controls but it instantly went back to -100%.

    STFT's both banks were normal looking and changing like normal. O2 readings both banks were normal looking, switching back and forth like normal. Only the bank 2 LTFT of -100% looks odd. Car is running great.

    I can post a log tomorrow if needed, it's not on this computer.

    What's causing this?
    2005 Vert Z51 MZ6
    Horsepower Sales 954-984-8040
    4:10's, FAST 92, A/R Headers w/cats, G5x3, .040 gaskets AFR 205 heads ORIG CLUTCH
    472rwhp/414rwtq
    Best pre-cam:1/4-1.730, [email protected]
    Best w-cam, pre-FAST 1/4-1.666, [email protected]
    Best w-cam & FAST 1/4-1.519, [email protected] DA-793
    Best w-cam & AFR heads 1/4-1.445, [email protected] DA-581 1/8-1.445, [email protected] DA-581
    Top speed 185 (so far...) 0-60 mph 2.59 sec (track)

    http://www.youtube.com/watch?v=DUX3UNFl124

  2. #2
    Tuner RedWS6 00's Avatar
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    I've never seen fuel trims go more than+/-25%.
    Check that you are logging the same fuel trims for both sides, there are about 8 PID's for fuel trims. Some SAE. Its easy to log the wrong one.
    You say you are logging the O2's switching, are you logging the front O2's, these are used to work out your fuel trims.

    If you can post a log we should be able to nail this problem. As the car is running okay, there cant be anything major wrong.

    When posting the log, can you post the config file too.
    2000 Red TA WS6 M6 in England, UK
    Patriot Stg.II Heads & 226/226-112 0.585/0.585 Cam. Corsa Cat back, F.A.S.T LSX Intake / F.A.S.T Fuel rails, Dynatech LT's/Y, Wisper Lid, ported MAF, 52lb/hr. 160 stat. !AIR, !EGR. Walbro 255, SPEC Stage II.
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  3. #3
    Quote Originally Posted by Joe_G
    Scanned a buddy's 98 C5 last night and his bank 2 LTFT was -100% across the board and not changing, bank 1 was normal, -3% or so, something reasonable. I cleared the LTFT's via VCM controls but it instantly went back to -100%.

    STFT's both banks were normal looking and changing like normal. O2 readings both banks were normal looking, switching back and forth like normal. Only the bank 2 LTFT of -100% looks odd. Car is running great.

    I can post a log tomorrow if needed, it's not on this computer.

    What's causing this?
    I would hazard a guess that because this is a 98 you have a 24 byte limit and if you have exceeded that then one of your PIDs will not read accurately, reduce your PIDs to under 24 bytes and try again and I suspect that will cure your issue. I am sure I have read this previously.

    Cheers

  4. #4
    Tuner Joe_G's Avatar
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    Quote Originally Posted by SSUte01
    I would hazard a guess that because this is a 98 you have a 24 byte limit and if you have exceeded that then one of your PIDs will not read accurately, reduce your PIDs to under 24 bytes and try again and I suspect that will cure your issue. I am sure I have read this previously.

    Cheers
    Well this very could be - I've got a LS2 and I just used my config file when scanning his car and I've got the pid's set up for my car and I know added a few from the stock config file.

    I'll post up the scan later today.

    Thanks boys!
    2005 Vert Z51 MZ6
    Horsepower Sales 954-984-8040
    4:10's, FAST 92, A/R Headers w/cats, G5x3, .040 gaskets AFR 205 heads ORIG CLUTCH
    472rwhp/414rwtq
    Best pre-cam:1/4-1.730, [email protected]
    Best w-cam, pre-FAST 1/4-1.666, [email protected]
    Best w-cam & FAST 1/4-1.519, [email protected] DA-793
    Best w-cam & AFR heads 1/4-1.445, [email protected] DA-581 1/8-1.445, [email protected] DA-581
    Top speed 185 (so far...) 0-60 mph 2.59 sec (track)

    http://www.youtube.com/watch?v=DUX3UNFl124

  5. #5
    Tuner Joe_G's Avatar
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    Here's the scans. Appreciate any and all comments.
    2005 Vert Z51 MZ6
    Horsepower Sales 954-984-8040
    4:10's, FAST 92, A/R Headers w/cats, G5x3, .040 gaskets AFR 205 heads ORIG CLUTCH
    472rwhp/414rwtq
    Best pre-cam:1/4-1.730, [email protected]
    Best w-cam, pre-FAST 1/4-1.666, [email protected]
    Best w-cam & FAST 1/4-1.519, [email protected] DA-793
    Best w-cam & AFR heads 1/4-1.445, [email protected] DA-581 1/8-1.445, [email protected] DA-581
    Top speed 185 (so far...) 0-60 mph 2.59 sec (track)

    http://www.youtube.com/watch?v=DUX3UNFl124

  6. #6
    Senior Tuner Russ K's Avatar
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    Like SSUte01 said, the 1998 only supports 24 bytes, your using 26. Remove the O2 mv pids to get down to 24 bytes max.

    Russ Kemp

  7. #7
    Senior Tuner mowton's Avatar
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    Quote Originally Posted by Joe_G
    Scanned a buddy's 98 C5 last night and his bank 2 LTFT was -100% across the board and not changing, bank 1 was normal, -3% or so, something reasonable. I cleared the LTFT's via VCM controls but it instantly went back to -100%.

    STFT's both banks were normal looking and changing like normal. O2 readings both banks were normal looking, switching back and forth like normal. Only the bank 2 LTFT of -100% looks odd. Car is running great.

    I can post a log tomorrow if needed, it's not on this computer.

    What's causing this?
    I saw the same thing on a friends 98 as well. I seem to remember it was both banks though, but I knew the trim(s) stated 100%. Car ran great as well, so I knew it was a false reading. I reloaded the .config and started the scan over and all was well again, was wierd.......

    The 98 is a strange beast
    2004 Vette Coupe, LS2, MN6, Vararam, ARH/CATs, Ti's, 4:10, Trickflow 215, 30# SVO, Vette Doctors Cam, Fast 90/90, DD McLeod, DTE Brace, Hurst shifter, Bilsteins etc. 480/430

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  8. #8
    Tuner Joe_G's Avatar
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    Quote Originally Posted by Russ K
    Like SSUte01 said, the 1998 only supports 24 bytes, your using 26. Remove the O2 mv pids to get down to 24 bytes max.

    Russ Kemp
    Perfect. Thanks for the help guys!!
    2005 Vert Z51 MZ6
    Horsepower Sales 954-984-8040
    4:10's, FAST 92, A/R Headers w/cats, G5x3, .040 gaskets AFR 205 heads ORIG CLUTCH
    472rwhp/414rwtq
    Best pre-cam:1/4-1.730, [email protected]
    Best w-cam, pre-FAST 1/4-1.666, [email protected]
    Best w-cam & FAST 1/4-1.519, [email protected] DA-793
    Best w-cam & AFR heads 1/4-1.445, [email protected] DA-581 1/8-1.445, [email protected] DA-581
    Top speed 185 (so far...) 0-60 mph 2.59 sec (track)

    http://www.youtube.com/watch?v=DUX3UNFl124

  9. #9
    Tuner in Training
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    This happened on my 05 CTS-V a few times. Disconnect, re-connect and it went away. Happened twice this last week.