1. Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

4l80e help

Discussion in 'All Other Transmissions' started by Wally tavera, Sep 25, 2016.

  1. Wally tavera

    Wally tavera New Member

    7
    0
    Sep 25, 2016
    Oregon
    1991 chevy suburban transmission shift hard 1st and 2nd no lock up in overdrive let I sit for 30 min drive again everything work good can drive for hours until I shut if off and start it up and and will act back up again. And this transmission was rebuilt 1500 miles ago.
     
  2. THEFERMANATOR

    THEFERMANATOR FRANKENBURBAN Staff Member Lead Moderator

    8,480
    1,540
    May 9, 2008
    ZEPHYRHILLS FL
    Sounds to me like either a loss of prime issue when it sits for extended periods, or some electrical issues. I remember there being a problem with the early 4l80e controllers being set to sensitive to loss of prime, and it causing limp mode on a cold start. Drive it through the gears to reprime the trans, shut it off, and when you restart it everything was fine. I'll have to try and search to find it again.
     
  3. Wally tavera

    Wally tavera New Member

    7
    0
    Sep 25, 2016
    Oregon
    I've been looking through all the electrical and I replaced all the sensors. checked the throttle position sensor it seems to be getting all the right volts it needs in there I'm just don't know what to do with it like I said it runs and drives fine down the road as soon as I shut the ignition off turn it back on then it goes into a hard shift and then I shut it off wait a few minutes again maybe 30 and then it works just fine
     
  4. Will L.

    Will L. Well-Known Member

    5,802
    3,138
    Jan 25, 2013
    Boulder City Nv
    Drain fluid and save. Pull the pan and double check the lower harness is not pinched under the pan gasket.

    Just rebuilt- WARRANTY?
     
  5. snarl95

    snarl95 Active Member

    230
    80
    Feb 22, 2014
    Edenton,NC
    Pull the connector on side of trans and see if there is fluid in the connector.
     
    WarWagon likes this.
  6. Wally tavera

    Wally tavera New Member

    7
    0
    Sep 25, 2016
    Oregon
    There was some oil in there once before I sprayed it out with the electrical cleaner
     
  7. WarWagon

    WarWagon Well it hits on 7 of 8...

    7,332
    1,306
    Nov 15, 2009
    AZ
    Ask the computer "why"? Should be a code in it.
     
  8. Wally tavera

    Wally tavera New Member

    7
    0
    Sep 25, 2016
    Oregon
    Well I reset my computer drovp my vehicle around and finally said just one code out of the whole system it shows 85 I think that is the prom error code what is that this thanks
     
  9. THEFERMANATOR

    THEFERMANATOR FRANKENBURBAN Staff Member Lead Moderator

    8,480
    1,540
    May 9, 2008
    ZEPHYRHILLS FL
    Code 85 is undefined ratio error, meaning the actual measured gear ratio by the controller is different than what it should be by to large a margin. I'm still digging for that tsb as I could have sworn code 85 was the one it caused, and the fix was a prom change. But I also found this bulletin that applies to early 4l80e's that have recently been rebuilt.
    https://www.google.com/url?sa=t&sou...FF5kv3wPPlcbTfcFg&sig2=BnWyw-6BKdWUuYYJMT-7og
     
    jrsavoie likes this.
  10. Wally tavera

    Wally tavera New Member

    7
    0
    Sep 25, 2016
    Oregon
    So should I change the prom and see what the heck happens I mean that's the only thing I could see it could be causing the havoc on the transmission no other codes come up
     
  11. THEFERMANATOR

    THEFERMANATOR FRANKENBURBAN Staff Member Lead Moderator

    8,480
    1,540
    May 9, 2008
    ZEPHYRHILLS FL
    Problem is finding one. GM has long since discontinued stocking them last I checked, and just finding part numbers is getting difficult.
     
  12. EWC

    EWC Active Member

    178
    37
    Jun 14, 2008
    Gas or diesel ? 2 or 4WD ?
     
  13. Wally tavera

    Wally tavera New Member

    7
    0
    Sep 25, 2016
    Oregon
    Gas 5.7 4x4
     
  14. EWC

    EWC Active Member

    178
    37
    Jun 14, 2008
    Put a scanner on it and see what the speeds are . The book also tells you to check the PSM ( pressure switch manifold ) , this lets the ECM know what gear is selected .
     
    jrsavoie likes this.
  15. Wally tavera

    Wally tavera New Member

    7
    0
    Sep 25, 2016
    Oregon
    I have replaced that too
     
  16. THEFERMANATOR

    THEFERMANATOR FRANKENBURBAN Staff Member Lead Moderator

    8,480
    1,540
    May 9, 2008
    ZEPHYRHILLS FL
    New doesn't mean good. You NEED to get a scanner on it and watch it when it does it to see what it is doing. Otherwise you're simply guessing at the problem.
     
  17. EWC

    EWC Active Member

    178
    37
    Jun 14, 2008
    Personally I would not reuse a pass thru connector if there was ATF coming out of it . Clean it once or to get you home but not in the long run . They have been redesigned . Your problem sounds like an electrical issue , than mechanical , which is why you need a scanner . Grounds can also be a problem .
     
  18. Burning oil

    Burning oil LeroyDiesel.com Vendor

    10,124
    1,444
    Jan 3, 2009
    Houston
    Seems to be a very common issue on DB2 with 4L80Es. My old 93 to the same thing. I never did fix it before selling it.
     
  19. deejaaa

    deejaaa Well-Known Member

    1,430
    201
    Sep 19, 2008
    Texas
    i converted mine to manual valvebody. it wasn't shifting out of 1st. figured it was a wiring issue and wasn't able to find it. also have TCC manual lockup.
    only problem is it needs a reverse lockout shifter and will need mounted on the floor.
     

Share This Page