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torque converter clutch "hunting"

Discussion in 'GM Powertrain' started by cascott325, May 19, 2009.

  1. cascott325

    cascott325 New Member 1000 Posts

    i have a question which could be caused by a faulty something or another in the fuel/air monitoring system. my truck, usually when maintaining a speed between 43 and 53 mph, not at any certain rpm, will kinda rev up and down, up and down, up and down... etc, almost like its about to down shift but it doesnt, it just keeps pulsing like that until i mash the gas a little more, and it normally only happens when i am going up a slight-moderate incline. do any of you think it could be due to a faulty O2 sensor, or maybe dirty injectors? or if it is another problem, i will post it in its proper place, but if it is related to a bad sensor then whatever. i also noticed it this weekend when returning from tenn, it did it but not as bad, at around 85 or so
  2. MrShorty

    MrShorty Moderator Staff Member 1000 Posts

    Sounds to me more like a transmission issue -- specifically like the torque converter clutch (TCC) is engaging/disengaging because the computer can't decide for sure what it wants to do. Does it do it if you drop the selector into D?
  3. cascott325

    cascott325 New Member 1000 Posts

    no, just in overdrive
  4. MrShorty

    MrShorty Moderator Staff Member 1000 Posts

    Really sounds like the TCC locking and unlocking. What happens is, in 4th gear, the computer decides the load is easy enough, so it locks the TCC. Locking the TCC increases the load on the engine just enough that the PCM decides to unlock the TCC. And so the PCM vacillates back and forth between locking/unlocking the TCC until you substantially increase the load (smash the throttle) or decrease the load (get over the top of the hill/downshift into 3rd). If this is your only symptom, I don't know how much I'd worry about it. Just get into the habit, when the transmission is "hunting" like that, simply downshift manually.
  5. cascott325

    cascott325 New Member 1000 Posts

    thanks mr shorty. sorry for kinda changing subject.
  6. noahraysanders

    noahraysanders New Member

    how can you fix this

    how can you fix this?
  7. MrShorty

    MrShorty Moderator Staff Member 1000 Posts

    I assume you are looking for a solution other than manually downshifting into third gear.

    Assuming no mechanical problems are present, and you are sure it is just "hunting" the first thing that comes to my mind is a custom tune that changes the PCM's thresholds for locking/unlocking the TCC.

    PS extracted these posts from O2 sensor thread and put them in their own thread.
    Last edited: Jun 1, 2009
  8. Jimmiee

    Jimmiee New Member 1000 Posts

    I believe he's fighting a surging problem and not a TC problem according to his other post he posted today.
  9. cascott325

    cascott325 New Member 1000 Posts

    thank you moderator who moved these posts. i am sorry i started a new topic. i planned on trying to copy and paste to a new thread, but you beat me to it.

    back on topic... i have noticed that since my fuel pressure has been acting up, it seems to be more prominent of a problem, yet still only happening going up hills, i think the problem causing my offset psi's is causing the strange fluxuations in power as well... hmmm, who'd of thunk it
  10. MrShorty

    MrShorty Moderator Staff Member 1000 Posts

    How is your fuel pressure fluctuating? I can't think of a better term, but the fuel pressure is "moderated" by engine vacuum. When engine vacuum is high (indicating less load on the engine), fuel pressure will decrease a little. When engine vacuum drops (indicating more load on the engine), fuel pressure will increase. If your fuel pressure is fluctuating consistent with engine vacuum, it probably is related to the changes in engine vacuum caused by changing load on the engine caused by the TCC locking/unlocking.

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