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2020 2500Hd feels like it is surging when towing a hill


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  • 4 months later...
On 3/16/2021 at 8:37 AM, Michael Hickman said:

I have a 2020 Silverado HD with the 6.6L gas and mine surges as well.  I notice it more when in 6th gear and I give it just enough gas to not downshift coming up hills.  Did you find a fix?  

Same here but it does it in most all gears. Really noticeable in 2nd to 4th between 1450 and 1700 rpm. 
 

No fix for it yet. Complain to your dealer and get it booked in otherwise gm will never look into it. 

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...

 

Quote

 

#20-NA-142: Shudder/Surging While Driving - (Feb 9, 2021)

Involved Region or Country

North America, Russia, Middle East, Israel, Palestine, Chile, Columbia, Ecuador, Paraguay, Peru and Thailand.

Condition

Some customers may comment that a surging condition is felt when driving.

Some technicians may find during diagnosis or performing PIP5504F, may identify the surging as a torque converter shudder.

Cause

This condition may be caused by additives in the transmission fluid may have been depleted during vehicle operation.

  • Some of these additives assisted with regulating a consistent slip rate of the clutches.

Correction

  1. Raise the vehicle.
  2. Remove transmission pan.
    • If metallic debris is present (similar to graphic above), remove transmission and replace the torque converter and replace the transmission filter. Refer to Torque Converter Replacement in SI.
    • If metallic debris is not present drain and clean the oil pan and reinstall transmission oil pan.
  3. Fill the transmission with 6 quarts of DEXRON VI Transmission Fluid following published Service Information.
  4. Lower the vehicle to a safe level on the hoist and operate the transmission through all 6 gear forward ranges, reverse and neutral.
  5. Remove transmission oil pan and drain, reinstall the oil pan.
  6. Fill the transmission with 6 quarts of DEXRON VI Transmission Fluid following published Service Information.
  7. Lower the vehicle to a safe level on the hoist and operate the transmission through all 6 gear forward ranges, reverse and neutral.
  8. Remove transmission oil pan and drain, clean pan and replace the transmission filter.
  9. Fill the transmission with 6 quarts of DEXRON VI Transmission Fluid.
  10. Set the fluid level following published Service Information.
  11. TCC SLIP CONTROL TEST RESULT

    TCC rpm slip peak to peak (at steady throttle)

    ACTION

    Note

    Normal (Callout 1)

    Below 20 rpm.

    Do nothing.

     

    Damaged (Callout 2)

    Near 0 to 100 rpm - erratic.

    Inspect transmission further

    Inspect transmission pan magnet for excessive metal accumulation.

    Degraded (Callout 3)

    Near 60 rpm - repeating.

    Flush transmission fluid. Refer to bulletin 20-NA-142.

    Shudder, surge, fish bite likely.

 

 

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Mines definetly not converter shudder. I’ve felt it before and it’s a fairly quick acting action (multiple times a second). The surge I feel is like  once or twice a second-if this makes any sense to others with the complaint. And has an audible rpm change. Is this what y’all are describing also?

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On 3/18/2021 at 1:50 AM, Another JR said:

Are you talking about heavy surging that is very noticeable, or about a very subtle oscillation? 

I wouldn’t call it heavy surging but it is noticeable.  I can’t see a change on the tach or feel it but I can hear it.  If I’m in a hard pull it’s fine I only notice it at part throttle usually in 6th gear when I give it a little gas but not enough to downshift. I had to take it to the dealer to fix a couple of  noises it was making and one was a loose bolt on the battery tray and they had to unhook the battery to fix it.  After picking it up and driving it a couple days I think the surge is better so I might be worth a try to unhook the battery and reset the computer.  

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I asked that question to try to rule out the torque converter shudder issue or a serious engine operating issue.  I have not experienced the TC shudder in a newer truck, but researched it heavily when researching for my new truck purchase.  Every description I read seemed to convey that it was not a subtle symptom. 

 

From what you describe it sounds very similar to something I notice on my 2004 Yukon XL with the 5.3.  When climbing a particular gentle hill near my home at about 40 mph, the throttle is clearly just slightly going up and down regularly at slightly faster than once per second even though I am holding the gas pedal at a fixed position.  It's very subtle, and passengers would not notice it unless I made them really listen for it.  It can barely be felt, but can be heard in the exhaust tone more easily.  My Yukon has 140k on it and it has done it since new, always on that one hill, and occasionally I'll note it in other similar gentle 35 to 45 mph climbs.  It does not occur on steeper climbs or at highway speed where the torque is higher.  I never remembered to ask the dealer service people about it in the times I've been in for service because it hasn't really bothered me, and because I think it's a normal characteristic of a control system design that is not perfectly optimized. 

 

I work in analysis and testing of aircraft engine control systems, both piston and turbine, so I know something about the design of digital engine control systems (although I would not claim to be an expert).  I have always assumed that what I was noticing in my Yukon was a slight instability of the throttle control loop that controls steady state operation (my Yukon is a fairly early throttle by wire design).  This would likely be due to the software not adequately matching the dynamic characteristics of the throttle plate actuator or the engine response, and either having slightly to much control loop gain or not enough of a damping provision.  That's just a mental model, of course, but it's the only thing I can think of that would cause that very slight throttle oscillation characteristic.  The characteristic on my Yukon is clearly not transmission or torque converter related. 

 

 

Edited by Another JR
clarify explanation
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On 3/19/2021 at 10:32 AM, Another JR said:

I asked that question to try to rule out the torque converter shudder issue or a serious engine operating issue.  I have not experienced the TC shudder in a newer truck, but researched it heavily when researching for my new truck purchase.  Every description I read seemed to convey that it was not a subtle symptom. 

 

From what you describe it sounds very similar to something I notice on my 2004 Yukon XL with the 5.3.  When climbing a particular gentle hill near my home at about 40 mph, the throttle is clearly just slightly going up and down regularly at slightly faster than once per second even though I am holding the gas pedal at a fixed position.  It's very subtle, and passengers would not notice it unless I made them really listen for it.  It can barely be felt, but can be heard in the exhaust tone more easily.  My Yukon has 140k on it and it has done it since new, always on that one hill, and occasionally I'll note it in other similar gentle 35 to 45 mph climbs.  It does not occur on steeper climbs or at highway speed where the torque is higher.  I never remembered to ask the dealer service people about it in the times I've been in for service because it hasn't really bothered me, and because I think it's a normal characteristic of a control system design that is not perfectly optimized. 

 

I work in analysis and testing of aircraft engine control systems, both piston and turbine, so I know something about the design of digital engine control systems (although I would not claim to be an expert).  I have always assumed that what I was noticing in my Yukon was a slight instability of the throttle control loop that controls steady state operation (my Yukon is a fairly early throttle by wire design).  This would likely be due to the software not adequately matching the dynamic characteristics of the throttle plate actuator, and not having enough of a damping provision.  That's just a mental model, of course, but it's the only thing I can think of that would cause that very slight throttle oscillation characteristic.  The characteristic on my Yukon is clearly not transmission or torque converter related. 

 

 

I feel you’re on point with your personal assessment. It’s almost as though the new DI control isn’t able to fine tune itself enough at low rpm, higher injection quantity when compared to it’s throttle signal input and is hunting to keep it within the parameters it wants. Could even be emissions related trying to keep it running clean at higher pulse widths so it’s constantly adjusting. 
 

If these damn tuning companies like HP or EfiLive would get off there asses and release some tuning capabilities it would be nice to get it on the dyno and log it to see just wtf it’s actually doing. IMO I feel even just changing some of the shift points and making other trans shift changes would go a long ways with driveability. 
 

I’m just glad I’m not the only one that has been experiencing this. 

Edited by L8T
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I edited my explanation of what i think is going on to recognize it's more likely the lag in engine response itself rather than lag in the throttle plate response that causes slight instability of the throttle plate control loop. 

 

 

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  • 6 months later...

Sorry everyone. I know this is an older thread but I have been searching for weeks and came across this today which almost describes my situation perfectly.  Looooong time reader (5 years or more) but I have never joined up until today.  

 

But I was hoping for some insight from anyone on this post or familiar with this issue.   

I have a 2021 2500HD  6.6 gas.  I pull a fifth wheel of around 11,500 lbs.   My issue is when I am accelerating while towing I start getting a jerking/misfire "fishbite" feel starting around 3000 rpm up to about 4000 rpm.  This started at about 12,000 miles on the truck.  It mainly happens in 3rd gear between 3200 rpm and 3800rpm but has started doing it in the end of 2nd gear and even 4th occasionally.     

 

I brought the truck to the dealer with the trailer attached and the tech rode with me. He felt it as well.  He brought along a laptop that was connected to my truck. He recorded some snap shots of all the data while it was doing it.  The data was submitted to GM and they noted that the slip speed was more than tolerances allotted. They recommended replacing the torque converted and inspecting the trans pump.  My pump had a few cracks so he replaced the pump rotor and torque converter.    I was hoping for it to be over.   However once I hooked to my trailer again, it was still there.   Just as bad as before.   We did another test drive and recorded the data again but he and another tech seem to be at a loss as to what is going on.    

 

Just FYI  it does it with or without tow/haul engaged, cruise on or off, air conditioning on or off, stabilitrac on or off... none of it matters.   I have even pulled it without the trailer plugged into the electrical to eliminate any trailer brake malfunctions...      It happens around the same RPM every single time.     I have pulled 4 other trailers the heaviest of them weighing about 7000lbs all bumper pull.  No issues present on any of them.       

 

I am waiting to hear back from the dealership still but looking for answers on my own 

 

 

Thanks!!   

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It very well could be torque converter shudder. However they replaced the torque converter under warranty and it is still doing it.  So idk what the odds of both of them being bad are.  I also installed timbrens last week to adjust the ride height thinking it may be drive line vibrations from the load changing the angle.  Although it handles better and doesn’t squat as much now, it’s still jerking at that rpm range.  

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