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Thread: trans not going into 4th gear even though log says it is?

  1. #1
    Junior Member
    Join Date
    Dec 2007
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    Default trans not going into 4th gear even though log says it is?

    well i just figured out that my truck hasn't been going into 4th gear at all. It will do 3rd gear tcc locked but that's it. i hooked the scan tool up today and checked it. it says it is in 4th gear and the tcc is locked but if i manually shift it to 3rd the tcc unlocks then locks again and the rpms go back to what they were before.

    truck is a 2005 ccsb z71 sierra 5.3, 3.42, 32" tall tires. The only thing done to the truck is a built trans, trailblazer torque converter, and a k&n intake. I've only done trans tuning.. Could the tb stall be causing the truck to not go into 4th gear? I loaded the stock tune back in and it still wont go into 4th gear.

    here is the current tune on the truck.
    Attached Files Attached Files
    has no idea how to tune!!

  2. #2
    Junior Member
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    Dec 2007
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    29

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    no one has anything that might help me out? im trying to figure out if its in the tune or if its the trans itself.
    has no idea how to tune!!

  3. #3
    Lifetime Member
    Join Date
    Mar 2006
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    4,798

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    Had this problem on my 02 TrailBlazer when I botched a shift kit and servo install. The PCM is commanding 4th lockup, however the trans isnt doing it. With your built trans, check the servo installation and if that doesnt do it, probably time for a rebuild...
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, starting the mods
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

  4. #4
    Member
    Join Date
    May 2011
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    69

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    im trying to help him with this issue also. he is out of town for a few days and wanted me to ask if there is a setting or something in efi live to make it go into 4th? I see you can make it hold 4th thats all i can find. just to make sure its not a tuning issue.

    i talked to my trans guy he thinks the servo or accumulator piston maybe the issue also.
    any other imput would be great thanks

  5. #5
    Lifetime Member
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    Grab a laptop and your FlashScan, use the Scan tool, connect to the truck, then click F12 DVTs. Select LS1B PCM, then click activate. Go to the Auto Transmission, and then get to like 50-60mph where it should go into 4th. Click the checkbox, then click Hold 4th. If it shifts, then its a tune problem. If it doesnt, then its a mechanical problem.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, starting the mods
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

  6. #6
    Member
    Join Date
    May 2011
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    69

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    Amesome thanks for your help
    99 ECSB 1500 6.0 lq9/243 2wd 3.42 in the works.
    Efans - CAI - Walbro 255lph - Eaton LSD
    BTR STAGE 3 truck cam - 60lb Inj - MP122HH
    FLT Level 5 - 3000 SC YANK
    Pacesetter LT's - ORY
    13.170 @ 103.33 Mph -

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