Results 1 to 9 of 9

Thread: 4l80e not shifting out of first

  1. #1
    Lifetime Member
    Join Date
    Aug 2012
    Posts
    238

    Default 4l80e not shifting out of first

    This is a 2002 6.0 with 4l80e. It has a digital dakota 8k pulse generator on it.

    Truck originally had a 3 wire dakota digital speed sensor and the shop tapped in the VSS high to the signal wire. I was called out to help diagnose and fix the problem of strange shifting. When I logged the data I noticed the VSS line was very choppy and snapping around 5-7MPH from actual speed. I told them to order a 2 wire DD 8k pulse generator, reflashed for the new pulse per mile. I then get a call that it won't shift out of first now. When I show up with my V2, connect and start logging, we go for a drive and the truck shifts fine. It felt like I came down for no reason. I did notice the speed was off by 15% so i made that correction and went for another drive. Then it was acting like before where it wouldn't shift out of first. I tried a new PCM with a good, known tune. Still same problem.

    I can use DVT and trigger shifts through all gears. It doesn't feel like it's commanding them. I am currently trying to get the Commanded Gear PID to work (It had an X through it and when I validated it and tried to connect it generates an error report when clicking the yellow or red record button, thread here https://forum.efilive.com/showthread...989#post247989)

    I would like to know what to test for IF i can get the commanded gear PID to work and it shows either A) it is not commanding a shift (and why isnt it, what are the triggers to make it command) and B) it is commanding the shift but it is not happening at the trans (despite being able to with DVT)

  2. #2
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003
    Posts
    27,752

    Default

    To determine when to shift, the trans module uses VSS and TP to lookup the shift tables...

    if either VSS or TP are not working right then there will be either no shifts, or all the shifts will happen in rapid succession.

  3. #3
    Lifetime Member
    Join Date
    Aug 2012
    Posts
    238

    Default

    I had a nice smooth VSS line. And TPS signal.

    After banging me head against the wall for a while I figured it out.

    Since the transfer case had a mechanical speedo, they put a 8000 ppm pulse generator on it. I then changed the current PPM to 8000 which I thought I had done before with successful results. Apparently that caused all my issues.

    Instead, I changed the trans pulse per revolution from 40 down to 3.6XX to get the PPM to say 8000. THAT made it all work again.

    I can only think that if the PPM number and the calculated ‘trans output revs per mile’ are off by a few decimal points then it won’t shift out of first

  4. #4
    Lifetime Member Doc's Avatar
    Join Date
    Oct 2005
    Posts
    733

    Default

    What kind of / brand of engine / tranny harness are you using? Had a doh moment a couple of years ago with a LS swap vehicle with a PSI of NC harness. Had similar issues. Called PSI and they had us check / swap the front and back speed sensor harness connections as the harness they supplied had enough slack to do the vice versa. Swapped the connections and it worked. Hope it's something simple like that.

    2000 Silverado Full Size 4x4: Forged 6.2, H/C F1R Procharger
    98A4 Z28: 02 PCM H/C Forged 347, 9" Moser 3.73
    V1 V2 99+up RR COS #5 OLSD Dual Stg N20
    www.eifalchemy.com
    www.greatamericancarwar.com

  5. #5
    Lifetime Member
    Join Date
    Aug 2012
    Posts
    238

    Default

    This was a stock harness so the speed sensors only installed one way.

    It was purely a programming issue. Using a pulse generator instead of the stock 40 tooth reluctor can cause issues if not programmed right.

  6. #6
    Lifetime Member
    Join Date
    Aug 2012
    Posts
    238

    Default

    So, what is the correct way to program for a 8,000 PPM genrator?

  7. #7
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003
    Posts
    27,752

    Default

    The pulse generators I've seen produce a poor quality square wave with lots of overshoot/spiking and ringing...

    have you looked at the signal using a high resolution oscilloscope...

    The VSS signal from the factory reluctor/sensor is very good quality.

  8. #8
    Lifetime Member
    Join Date
    Aug 2012
    Posts
    238

    Default

    What do we do if we have a original cable driven speedometer on an old transfer case behind a electronic trans?

  9. #9
    Lifetime Member
    Join Date
    Aug 2012
    Posts
    238

    Default

    The shop who did the engine swap installed the dakota digital 128k 3 wire sensor for the speedo then tapped the VSS high signal wire into the signal wire in the dakota sensor. That signal was indeed choppy and all over the place. That’s when I told the customer to pull the speed signal directly from the pcm output and get a dedicated 2 wire pulse generator (dakota 8k which is a sine wave signal) to feed the pcm. That signal is smooth as butter.

    It’s when I tried programming for the 8k pulse per mile that we had shifting problems. Not going out of first.

Similar Threads

  1. 4L80E shifting issue
    By TransAm-Z in forum 4speed RWD/FWD Transmission Tuning (incl T42)
    Replies: 6
    Last Post: May 21st, 2014, 01:54 PM
  2. 4L80E WOT shifting problem. 1st-2nd bounce rev limiter!
    By TransAm-Z in forum 4speed RWD/FWD Transmission Tuning (incl T42)
    Replies: 7
    Last Post: August 20th, 2013, 09:41 AM
  3. 4L80E Shifting Soft and Slow (tune attached)
    By LastCall in forum 4speed RWD/FWD Transmission Tuning (incl T42)
    Replies: 18
    Last Post: January 13th, 2012, 07:19 AM
  4. 4L80E shifting soft
    By BlackSS in forum 4speed RWD/FWD Transmission Tuning (incl T42)
    Replies: 0
    Last Post: November 19th, 2011, 03:05 PM
  5. 4L80E rough shifting issues
    By bekmwan in forum 4speed RWD/FWD Transmission Tuning (incl T42)
    Replies: 6
    Last Post: September 26th, 2009, 01:03 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •