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Weird downshifting.

Discussion in 'Technical Chat' started by Andrew H, Jun 20, 2010.

  1. Jun 20, 2010 at 12:52 PM
    #1
    Andrew H

    Andrew H [OP] What is this "search" you speak of?

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    When I let off the gas to coast it feels like my truck has a retarder system that slows it down and drops to a lower gear right away. Does anyone else have this issue? I searched the Tranny flash TSB but I thought that was just to help it shift smoother into higher gears.

    Oh yeah its an automatic 4.0 with no mods to engine.
     
  2. Jun 20, 2010 at 1:00 PM
    #2
    Andrew H

    Andrew H [OP] What is this "search" you speak of?

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    Found my answer. I read the TSB wrong. Mods you can delete.

    "To enhance shifting performance and smoothness below 20 mph during the 2-1 downshift on vehicles equipped with an A750 transmission, the Engine Control Module/ECM"

    Edit - dangit I am going thru the TSB again and it says "ONLY WHEN ACCELARATING".
     
  3. Jun 20, 2010 at 1:07 PM
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    SlurpeeBlueMetallic

    SlurpeeBlueMetallic FFFFFFUUUUUUUUUUUUUUU...

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    Normal. The fuel injectors kick off while coasting at a sufficient speed. It feels like a downshift but if you look at your tach the RPMs shouldn't change immediately. If you continue to slow down while coasting then you will eventually downshift.


    The TSB you're reading typically happens when accelerating at slow speed, often when rounding corners or something similar. You try to accelerate but the truck seemingly can't find the right gear so it lags a second or so before acceleration starts. I had this as well and that TSB cleaned up the behavior almost completely.
     
  4. Jun 20, 2010 at 1:11 PM
    #4
    Andrew H

    Andrew H [OP] What is this "search" you speak of?

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    Thanks man. rep given.
     
  5. Jun 20, 2010 at 1:13 PM
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    jandrews

    jandrews Carolina Alliance Southwest Region Ambassador

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    TSB is for acceleration.

    The slight slowing that feels like a downshift is a normal designed part of the trucks...I love it...feels almost like an engine brake assist :p
     
  6. Jun 20, 2010 at 4:51 PM
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    SlurpeeBlueMetallic

    SlurpeeBlueMetallic FFFFFFUUUUUUUUUUUUUUU...

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    You're welcome. It took me a bit to get used to the injectors turning off while coasting but I worked it into my driving style and it's a major way to get good mileage out of these trucks.

    If you're having cornering/acceleration problems like described in the TSB I highly recommend the re-flash as it makes driving around town and in parking lots much smoother.
     
  7. Jun 20, 2010 at 5:04 PM
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    Andrew H

    Andrew H [OP] What is this "search" you speak of?

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    No the cornering and acceleration is fine. Well I am assuming it is I havent felt anything strange. Just wasn't used to the feel of the fuel injectors shutting off you like explained. Only my second week owning the 2nd gen so I am sure I'll get used to it.
     
  8. Jun 20, 2010 at 5:05 PM
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    MontanaTaco

    MontanaTaco Well-Known Member

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    I get this all the time and it is really annoying, I'm guessing you go to a dealer to get this done? Or can I use a scanner?
     
  9. Jun 20, 2010 at 5:28 PM
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    SlurpeeBlueMetallic

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    For the weird shifting at low speeds? Check the TSB here and take it to a dealer if you're still under warranty. It makes world of difference.
     
  10. Jun 20, 2010 at 6:49 PM
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    MontanaTaco

    MontanaTaco Well-Known Member

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    My 08 does the weird shifting, is this only for 09's?
     
  11. Jun 20, 2010 at 6:51 PM
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    SlurpeeBlueMetallic

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    Whoops, I missed that in your info... bump to see if anyone with an '08 had similar and maybe knows of another TSB.
     
  12. Jun 20, 2010 at 6:58 PM
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    Zombie Runner

    Zombie Runner Are these black helicopters for me?

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    it took me a while to get use to the engine braking but it helps save gas and less wear on the brakes as well
     
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