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Thread: 0411 Transmission Flaring - Tuning or Trans issue

  1. #16
    Fuel Injected!
    Join Date
    Oct 2013
    Posts
    1,022
    I'm just trying to post how the transmission works. The PSI stuff in the PCM is all labelled wrong since it's really more of a percentage where 0-96 is 0-100% of line pressure which is about 50psi to 180psi on a stock transmission. It's easier to setup the transmission when you actually understand what the PCM is doing. As for LRT, I can't help that he doesn't like being told he is wrong, but I'm not coddling him and letting him pass his wrong information as fact just to make sure his ego doesn't get bruised.

    As for your transmission - either it was an internal issue or the PCM was rapidly shifting it between 1st and 2nd gear. At 0 throttle you have a 1mph spread in the shift speed. The speed has to go over 14mph to upshift and below 13mph to downshift. So, unless your speed signal was fluctuating by at least 1mph, the PCM should not have been rapidly shifting back and forth between gears.

    You should be able to check the shifter cable by holding the shifter so the detent doesn't do anything and then moving the shifter so you feel where the transmission clicks in. For example, I have a floor shifter that can shift between N and OD without pressing the button. So, to check I hold the button and move the shifter to N and then release the button and try to move the shifter to R. It's adjusted right when the shifter just barely moves before hitting the stop in the shifter. I then checked OD and other gears a same way.

    Overall, my feeling is that a big part of making an automatic vehicle fun for you to drive is tuning the transmission. On my stuff, I've probably done at least as many tunes for transmission shifting compared to engine tuning. On my pickup, I licensed it with HP tuners just to re-tune the transmission.

    And you should pick-up a line pressure gauge if you want to be verifying the transmission is OK and also tuning it. It's a similar importance as using a wideband for the engine.
    Last edited by lionelhutz; 10-06-2017 at 06:51 AM.

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