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Thread: 8L90 TCC Locks and Unlocks Every Eight Seconds

  1. #1

    8L90 TCC Locks and Unlocks Every Eight Seconds

    Customer has a 2016 Cadillac ATS-V with 8L90 transmission and 12,000 miles on the odometer. Engine, transmission and tune are all completely stock. The problem is exhibited in cruise control while traveling down a highway. The following behavior is clearly visible while creating a log file while in cruise: while on the (at least somewhat level) highway, set the cruise control to the speed limit. The exact speed doesn't matter much since the problem and replicated at speeds from 50 to 90 mph. Begin logging and monitor the TCC line pressure. One can watch the TCC line pressure slowly begin to 'leak' down. Once the pressure has decreased to some point (about 29 at 70 mph), the torque converter unlocks. This can also be seen as a rise in the engine speed of about 200 rpm or so. TCC pressure is quickly restored (as this only takes about a second) and the converter again locks, the engine speed decreases appropriately and the TCC begins slowly decreasing only to repeat this cycle. This entire process is repeated about every eight or nine seconds indefinitely.

    Customer has spent hours at the dealer, took them for rides to demonstrate the behavior, logged a service incident, and involved the District Manager for "Aftersales" who eventually started dodging his calls. The local dealer has replaced the converter, re-flashed the car, changed to the latest-and-greatest fluids and now states that there is nothing else they can do. As an aside, the local dealer Service Manager also drives one. As soon as the customer demonstrated the behavior in his car, they immediately returned to the dealership and went for a ride in his car. It did the same thing. The Aftersales Manager 'talked to someone in Detroit' who has one, and confirmed the same behavior. Their conclusion was that since they ALL drive that way, they are performing as designed.

    I spent a few weeks working on this from a tuning perspective, and was never able to eliminate the issue. Wondering if anyone else has run across this before and if so, were you able to resolve it with tuning?

    I've attached the stock tune file and a scan clearly showing this issue.

    Thanks in advance!
    Attached Files Attached Files
    1998 Pontiac Grand Prix GTP (first 3800 FWD in the tens), 9.499 @ 145.13 mph
    1998 Pontiac Firebird (first 3800 RWD in the eights), 843 whp, 8.991 @ 152.12 mph, driven by Tim King
    1999 Pontiac Grand Prix GT (first 3800 FWD in the eights), 8.902 @ 154.90 mph, driven by Bob Cook
    2000 Pontiac Bonneville SSEi (first 3800 Bonneville in the twelves, elevens and tens), 10.711 @ 125.71 mph, driven by Ed Morad
    2008 Pontiac G8 (first G8 in the tens), 10.727 @ 129.87 mph
    2018 Cadillac ATS-V, 619 whp

  2. #2
    Tuner in Training
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    I know the 8l90 and 8L45 have an inherent stumble built in. To the point where there is a class action building.

    You should try to find the newly released factory tuning for the 17-19 8l90. I believe their was a recall/update for the 8 speed to help fix some of the shuttering issues. If you can look at the new factory tune and compare it to your factory tune it may give some answers.

    I wish the dealer would load the new tune on my 15i yukon with the 8l90. I have the shudder at 35 mph ish and it seems to drop out of gear when slowing to a stop.

  3. #3
    Quote Originally Posted by fifty
    I know the 8l90 and 8L45 have an inherent stumble built in. To the point where there is a class action building.
    We have heard that's coming. However, we were hoping to find a way to tune around this, rather than having to wait six or twelve more months for a solution.


    Quote Originally Posted by fifty
    You should try to find the newly released factory tuning for the 17-19 8l90. I believe their was a recall/update for the 8 speed to help fix some of the shuttering issues. If you can look at the new factory tune and compare it to your factory tune it may give some answers.
    We are using O/S 24281915, which appears to be the latest factory calibration.


    Thanks for your input!

  4. #4
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    Shudder

    Refer to this bulletin. #16-NA-175: Shake and/or Shudder During Light Throttle Acceleration Between 25 and 80 MPH (40 and 128 KM/H) at a Steady State - (Oct 11, 2018) . The fluid comes in bottles and must be shook up to get the additives settled on bottom of bottle or the problem will not be corrected. Also 200 miles accumulated before re-evaluating shudder. I have repaired a number of vehicles if performed correctly.
    Attached Files Attached Files
    Last edited by DGS; 1 Week Ago at 06:59 PM.

  5. #5
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    Thank you for this

  6. #6
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    There will be an updated bulletin with a new fluid part number and flush procedure in First Qtr 2019. Read red highlight in bulletin. Just an additional heads up.
    Last edited by DGS; 1 Week Ago at 07:24 PM.

  7. #7
    Quote Originally Posted by DGS
    Refer to this bulletin. #16-NA-175: Shake and/or Shudder During Light Throttle Acceleration Between 25 and 80 MPH (40 and 128 KM/H) at a Steady State - (Oct 11, 2018) . The fluid comes in bottles and be shook up to get the additives settled on bottom of bottle or the problem will not be corrected. Also 200 miles accumulated before re-evaluating shudder. I have repaired a number of vehicles if performed correctly.
    Appreciate you posting this. Seems to be specifically targeting the 'shudder' many people with these transmissions report. Do you think this might also help with the TCC locking and unlocking every eight or nine seconds that this customer is experiencing?

  8. #8
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    The shudder that I have noted on test drives prior to repair comes in rhythmic cycles. The computer monitors tcc slip, so the pressure would be adjusted to maintain the spec.. I do know that it has been completely eliminated following the bulletin on most vehicles. I always update the cals when repairing, especially with this issue. Some early vehicles had internal tcc clutch leaks and required a new torque converter. This could explain the symptom you are describing. If the bulletin and cals do not repair, it gets a converter. This affects numerous models, so I can't tell off hand if yours would need a cal update. It's just routine for me to follow what I stated. In some cases, I'm performing updates for free, but I know I'm giving the customer the best outcome. Can't speak for what others do. If you can't get this done right, find another dealer and/or press GM to get resolved. Where I work, the customer comes first. I have also had a number of coil/plug misfires/failures. Put in manual 4th. at lowest speed possible to lug engine and full throttle to load. You may pick up some misfires. I've put multiple coils/plugs on the same vehicle.
    Last edited by DGS; 1 Week Ago at 08:03 PM.

  9. #9
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    As for your 15 Yukon, this should apply. Assuming your under warranty, you should be able to get the updates. If you have complained before and are out of warranty, they should update the cals.. or they should work with you on the out of warranty cost.

  10. #10
    Tuner in Training
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    I wish. I have a friend who over the past 22 years, has worked for the local ford, gm and Chevy dealers (he now works
    For the county corps yard). All five (1 GMC, 2 Ford and 2 Chevy) have management that encourage warranty denial. The mexhanics are happy to do this because they and they service writers get paid more per Job. More book hours and higher hourly rate on a customer pay job. He said the factory reps are happy with this mentality too because it’s less money they manufacturer pays out.

    Sadly it leaves customers with the short end of the stick. Neither of my local Chevy dealers will Work on a/c and I’ve found it’s because the new a/c chemical is a nightmare and the machine is expensive. So the dealers blame lack of a/c in the summer on hot temps. Even when the new a/c lines are corroded and leaking from faulty soldering.

    It’s a two hour drive minimum, no traffic, each way to the next gm/Chevy dealer.

    I was told with my Chevy Colorado zr2, two weeks old, 300 miles on the clock, that they were going to void my warranty ty because I took it offroad (it was dirty on the undercarriage froma fire road). They told me gm instructed them that “Off-roading is abuse” .

    I called gm and they told me that they rely on and trust their dealer network to
    Identify abuse caused failures. (I was there for corroded a/c lines and lack of cold air)

    Flocking bs.
    Last edited by fifty; 1 Week Ago at 08:27 PM.

  11. #11
    Quote Originally Posted by DGS
    The shudder that I have noted on test drives prior to repair comes in rhythmic cycles. The computer monitors tcc slip, so the pressure would be adjusted to maintain the spec.. I do know that it has been completely eliminated following the bulletin on most vehicles. I always update the cals when repairing, especially with this issue. Some early vehicles had internal tcc clutch leaks and required a new torque converter. This could explain the symptom you are describing. If the bulletin and cals do not repair, it gets a converter. This affects numerous models, so I can't tell off hand if yours would need a cal update. It's just routine for me to follow what I stated. In some cases, I'm performing updates for free, but I know I'm giving the customer the best outcome. Can't speak for what others do. If you can't get this done right, find another dealer and/or press GM to get resolved. Where I work, the customer comes first. I have also had a number of coil/plug misfires/failures. Put in manual 4th. at lowest speed possible to lug engine and full throttle to load. You may pick up some misfires. I've put multiple coils/plugs on the same vehicle.
    Very much appreciate you sharing all this information.

    In this case, the TCM had already been flashed with the latest update. I verified this in HP Tuners. This did not resolve the issues, so the dealership replaced the torque converter. When that didn't take care of the issue they changed their tune and said it was normal for the TCC to lock and unlock every eight or nine seconds.