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Thread: not downshifting

  1. #1
    Senior Member SexySilhouette's Avatar
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    Unhappy not downshifting

    This started very suddenly tonight. After a WOT run with a Nissan. Van was fully warmed up.

    2 days ago, i replaced the vacuum modulator. It was bent and broken.

    last year, Jiffy Lube fleeced my wife for $150 to flush the trans and it's been acting screwy since - slipping from 3rd to 4th. Replacing the modulator fixed that.

    It downshifts at WOT on the freeway, TCC kicks in too.

    If I manually shift into 1st, it starts in 2nd but it takes off normally for taking off in 2nd gear.

    If it needs a trans, I will sell it, as much as I don't want to.
    Jay



  2. #2
    Senior Member turbokinetic's Avatar
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    How many miles ago did you replace the modulator? I know that the 440T4 trans will make second-gear starts if the modulator is set too high. But yours is a 4T60E if I'm not mistaken.

    The first thing I would do is put in some "sticking valve additive" such as K&W Trans-X. Allow that to circulate as you warm it up fully. Then get on a long straight stretch of road with little traffic, and shift from manual 1 to 2 to 1 to 2 back and forth. Make sure you are going at a speed where it would be able to shift down and up. This will put alternating hydraulic pressure on the stuck valve and work it back and forth. Hopefully after 20 or 30 tries it will start to shift again.

    If not, then you may need to change a shifting solenoid valve. They are under the end-cover of the trans.

    Hope this helps!
    David

  3. #3
    Senior Member SexySilhouette's Avatar
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    Thanks David, I was too tired and too pissed to mention that it is indeed a 1995 Silhouette 4T60E.

    I replaced the modulator Sunday and put maybe 30 miles on it. The old one was broken/bent.
    Last edited by SexySilhouette; 08-27-2010 at 01:06 AM.
    Jay

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    Senior Member turbokinetic's Avatar
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    Let us know how the fluid additive helps!

    David

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    Senior Member SexySilhouette's Avatar
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    Well, I smacked the ECM while taking off in the van one last time............................F****r took off like a bat out of hell. I have all gears again.

    Time to go find an ECM.

    Which would coincide with some other problems i'd been having like a few weeks ago when i was driving up the 183 frontage road and the speedo said I was doing 125 MPH at an actual 30 MPH, the ABS and brake lights coming on, ect...

    Jay

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    Check your electrical connections first; on my '96 GMC Sierra I had a bunch of screwy electrical things going on, and all it was was the main connection terminal on the underhood fusebox was loose....cost me a $70 diagnostic fee.

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    I do want you to check your grounds if you can as well as making sure all of the connections at the PCM are not corroded...

    Now, I will tell you that the 94-95 3800 C/H and U Body PCM is one of the worst PCM's ever... It will never let you know its entering failure mode... It will just simply fail...

    The second gear start is more along the lines of Limp Home Mode... Read that PCM for codes before you doom it..

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    Oh yeah! Pull the VSS and clean any debris off of it, it could be causing the speedo to go wacky. Just a little buildup of crap can really screw it up.
    -Andy

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  9. #9
    Senior Member SexySilhouette's Avatar
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    Quote Originally Posted by Jr's3800 View Post
    I do want you to check your grounds if you can as well as making sure all of the connections at the PCM are not corroded...

    Now, I will tell you that the 94-95 3800 C/H and U Body PCM is one of the worst PCM's ever... It will never let you know its entering failure mode... It will just simply fail...

    The second gear start is more along the lines of Limp Home Mode... Read that PCM for codes before you doom it..
    Done and done. no codes.
    Jay

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    Have you done anything else to the van or have you replaced the PCM? Just interested to know what the solution was...

  11. #11
    Senior Member SexySilhouette's Avatar
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    Cool

    All I've done is drive it. I haven't even replaced the PCM yet. No problems at all.

    I will get a PCM in a week or so...Just to make my wife happy.
    Jay

  12. #12
    Senior Member Prospeeder's Avatar
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    Sooo id like to know why in the HELL its destroying the vacuum modulators........
    "Pontiac, Of Course"
    1990 Pontiac Turbo Grand Prix 3.1T
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