Results 1 to 8 of 8

Thread: 4L80E WOT shifting problem. 1st-2nd bounce rev limiter!

  1. #1
    Junior Member
    Join Date
    Mar 2010
    Posts
    26

    Default 4L80E WOT shifting problem. 1st-2nd bounce rev limiter!

    I'm not sure if there is something wrong with the tune or my intermediate clutches are starting to fail... Problem is the 1st-2nd gear shift is not happening soon enough and engine is bouncing off rev limiter. I have posted a log and a screenshot showing that the "GM.GEAR" PID is not switching to 2nd gear until around 63mph or 7440 rpm. The tune I posted shows the 1st-2nd WOT shift commanded at 6200rpm and the part throttle shift should happen at 50mph. Also if you notice 2nd-3rd gear is off from the tune as well. WOT=7000rpm and it is actually shifting around 6465rpm.

    Does the GM.Gear PID represent when the gear is commanded to shift or does it represented what the pressure switch sees in the trans?

    Thanks!

    Click image for larger version. 

Name:	Rev-Limit.jpg 
Views:	370 
Size:	130.1 KB 
ID:	15692
    Attached Images Attached Images
    Attached Files Attached Files

  2. #2
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003
    Posts
    28,403

    Default

    You need to set the WOT downshift MPH below the corresponding WOT upshift MPH...

    i.e.
    - D0925-27 should be below D0910-12,
    - D0930-32 should be below D0915-17,
    - Do935-37 should be below D0920-22;



    also, set the WOT shift RPM's lower than what you have (say 5000 rpm), and then when you do get the WOT shifts occuring bump the WOT shift RPM's back up...

    but note that both WOT shift RPM and WOT shift MPH must be met, so keep either one of them lower than what is needed (but keep in mind what I said above).


    Also, look at some 4L80E files and set B4601 to be similar.


  3. #3
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003
    Posts
    28,403

    Default

    Quote Originally Posted by TransAm-Z View Post
    ...

    Does the GM.Gear PID represent when the gear is commanded to shift or does it represented what the pressure switch sees in the trans?

    ...
    GM.GEAR represents when the PCM switches the solenoids.


    There are no gear pressure switches in the 4L80E or the 4L60E (the pressure switches read the pressures in response to the manual valve, not the current gear).

  4. #4
    Junior Member
    Join Date
    Mar 2010
    Posts
    26

    Default

    Thanks for the fast reply Joecar!

    I am still a little confused though as the "stock" Silverado tune from Holden-Crazy I started with has the tables very similar to mine. (D0910 - D0925)

    What you are saying makes sense to me, I just don't understand why there are multiple tables being used... I assume from what you stated above that the PCM will look at both tables (RPM AND VSS WOT) and shift upon the last criteria meet?

    Click image for larger version. 

Name:	Stock-Silverado.jpg 
Views:	392 
Size:	408.6 KB 
ID:	15696

  5. #5
    Senior Member
    Join Date
    Jul 2005
    Posts
    188

    Default

    Quote Originally Posted by TransAm-Z View Post
    Thanks for the fast reply Joecar!

    I am still a little confused though as the "stock" Silverado tune from Holden-Crazy I started with has the tables very similar to mine. (D0910 - D0925)

    What you are saying makes sense to me, I just don't understand why there are multiple tables being used... I assume from what you stated above that the PCM will look at both tables (RPM AND VSS WOT) and shift upon the last criteria meet?

    Click image for larger version. 

Name:	Stock-Silverado.jpg 
Views:	392 
Size:	408.6 KB 
ID:	15696
    Yess, speed and rpm MUST be met before an upshift will be performed. Kinda like needing a bullet and a trigger pull in order to fire a gun.

    In this equation Bullet + Trigger Pull = Gunshot
    Bullet=Speed
    Trigger Pull=RPM
    Shift=Gunshot

    peace
    Hog
    1997 rcsb stock L31 longblock, Marine Intake with 28# EV6 injectors, L35 2700 stall TC,Hooker LT's 2.007 60ft

  6. #6
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003
    Posts
    28,403

    Default

    Quote Originally Posted by TransAm-Z View Post
    Thanks for the fast reply Joecar!

    I am still a little confused though as the "stock" Silverado tune from Holden-Crazy I started with has the tables very similar to mine. (D0910 - D0925)

    What you are saying makes sense to me, I just don't understand why there are multiple tables being used... I assume from what you stated above that the PCM will look at both tables (RPM AND VSS WOT) and shift upon the last criteria meet?

    Click image for larger version. 

Name:	Stock-Silverado.jpg 
Views:	392 
Size:	408.6 KB 
ID:	15696
    Some of the stock truck files contain "wrong" values (and cheat by using the Throttle Kickdown tables, which interferes with the PT upshift/downshift tables).


    Yes, PCM looks at 3 criteria for WOT shift: WOT RPM, WOT upshift MPH, and WOT downshift MPH...

    WOT RPM and WOT upshift MPH must both be met... and WOT downshift MPH must be below WOT upshift MPH.

  7. #7
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003
    Posts
    28,403

    Default

    lol, cars and guns, Hog has an interesting analogy

    chamber a round = WOT MPH
    pull trigger = WOT RPM

    (or vice-versa depending on which one is met first)

  8. #8
    Junior Member
    Join Date
    Mar 2010
    Posts
    26

    Default

    Thanks for the help! I'll make sure the bullets are in the gun this time=]

    I will test it tonight to see if all is better. Any idea what causes the trans to shift at all when these tables are messed up?

    Amazes me that I haven't blown this thing up yet! This trans has made about 50 passes @ aprox 1000 RWHP...

Similar Threads

  1. 1st to 2nd shift slipping at WOT
    By Mayhem in forum 4speed RWD/FWD Transmission Tuning (incl T42)
    Replies: 5
    Last Post: February 21st, 2012, 04:13 AM
  2. Why does 1st gear slam into 2nd? 4L80E translplant
    By 1SlowHoe in forum Gen III V8 Specific
    Replies: 82
    Last Post: May 22nd, 2010, 08:47 AM
  3. Transmission shifting / Rev limiter
    By zapp168 in forum Gen III V8 Specific
    Replies: 5
    Last Post: March 20th, 2008, 09:42 AM
  4. Hitting the rev limiter on the 2-3 shift at WOT...
    By waveoff in forum 4speed RWD/FWD Transmission Tuning (incl T42)
    Replies: 7
    Last Post: November 14th, 2007, 10:23 AM
  5. Rev limiter problem?
    By 67SS509 in forum General (Petrol, Gas, Ethanol)
    Replies: 5
    Last Post: January 22nd, 2006, 04:51 AM

Posting Permissions

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