2021 Denali - Vehicle Knock, Stutters, Surges, Rough Acceleration - In Auto Mode, After Lifting Rods Replaced

[jepaul2198]

Then it sounds more like a front driveline/transfer case issue. A savvy dealer should be able to isolate that and/or detect a problem….

I'm 0 for 2 thus far on that. The frustrating part so far is each dealer, when I bring it in, had test driven it first with me so I can confirm they agree there is a problem. Each has agreed there is a problem until they go back to take a look at it and say they can't find anything wrong with it and GMC says to drive it in 2WD anyway.

 

[jepaul2198]

What are lifting rods you are referring to??? Or do you mean pushrods inside the engine?

I might be using the wrong words. But lifting and rods are both in this description.

PIP5776C Chevrolet Technical Service Bulletin

PIP5776C Chevrolet Technical Service Bulletin

www.tsbsearch.com

Maybe I should be saying "Bent or broken rod led to a collapsed lifter?"

 

[WalleyeMikeIII]

If you had the well known lifter/collapsed lifter issue, that issue is resolved by removing the heads, inspecting and repairing as needed the valve train, the pushrods, and the lifters; as well as the cam; if needed.
Sounds like that was accomplished -- that is an engine issue.
If that issue were still happening; you would notice it in idle (Transmission in park or neutral) and while driving (transmission in Drive or Reverse or any of the manual forward gears).

You describe an issue that only manifests itself when you have the transfer case set to "Auto" and you are moving.
Thus, the conclusion is you have a driveline issue.
What you don't mention is whether you have a 2 speed transfer case or a single speed (ie, do you have 2High, Auto, 4High, and 4Lo, or do you only have 2High, Auto and 4 High?)

Regardless...if you can demo this issue to a competent service advisor/tech, and demo that it goes away when in 2High, then that same competent service tech should be able to diagnose.

Your powertrain (engine, transmission, transfer case) are covered under the powertrain warranty to 5yrs, 60k miles...so rest easy.

I can tell you, I have a Denali w/ the 2 speed transfer case, and I can hardly detect a difference in the vehicle between being in 2 High and Auto...and given the winter we have had, I have had it in Auto quite a bit. It's smooth as butter.

For some more details on how this transfer case works, suggest doing a little google search for GM Autotrak transfer case. Here is one article.

How Does 4WD Auto Work? Unveiling The Mystery Behind The Technology! - 4-Wheel Drive Guide

How Does 4-Wheel Drive Auto Work? 4-A EXPLAINED. 4WD auto functions by sending power only to the rear wheels until traction is lost. It engages the front wheels by activating an electric motor mounted on the transfer case which engages a metal fork that applies pressure to a set of friction...

4wheeldriveguide.com

Net, you need to find a dealer who is willing to listen; tell them to drive a pickup or full size SUV from the lot and see if it does the same thing...it should not.

You could have issue w/ CV Joint, TransferCase, Hubs, Transmission (although I doubt it, since it doesn't do it in 2WD), Front Drive Axle, etc...
Stick to your guns, regardless of whether they say you should or should not be driving in Auto, the vehicle in Auto does not tend to bind up, make noises, etc.
If you put it in 4hi, and drive on dry pavement, you could get some of what you are saying <--- don't do this.

 

[Pro299]

OK, now that we understand you were referring to the well known lifter repair (which in your case included at least one bent push rod), we have a real head scratcher. That repair is a "top of the engine" procedure and normally one would not expect that to have any impact on 2/4WD operation. Hard to imagine how the repair and your symptoms could be related. It could be coincidental, or maybe a wire harness or connector got pinched, control module communication was compromised or some other incidental component was accidently hosed during the repair. Unlikely, but stuff happens. I would back off insisting that the repair caused a problem and just treat it like a separate issue. It may take a really good tech to diagnose and I know those are getting hard to find. Good luck.

 

[jepaul2198]

OK, now that we understand you were referring to the well known lifter repair (which in your case included at least one bent push rod), we have a real head scratcher. That repair is a "top of the engine" procedure and normally one would not expect that to have any impact on 2/4WD operation. Hard to imagine how the repair and your symptoms could be related. It could be coincidental, or maybe a wire harness or connector got pinched, control module communication was compromised or some other incidental component was accidently hosed during the repair. Unlikely, but stuff happens. I would back off insisting that the repair caused a problem and just treat it like a separate issue. It may take a really good tech to diagnose and I know those are getting hard to find. Good luck.

Thanks Pro. I appreciate the guidance. Note just 6 days ago a separate post was made with almost identical issues from. Cdip01 - https://www.tahoeyukonforum.com/threads/4wd-auto-problem.139109/

I got the message from the dealer yesterday saying they performed all the recal work and my car is ready. That I should drive it in 2WD as GMC recommends. I pushed back hard asking them to please drive it around the block a few times and then drive one on the lot around. The differences will be impossible to miss. I think, simply my opinion, is the dealer(s) don't know what to do if there are no warning lights, codes, or easy fix that pops up when they search their internal help menu. Because my problem is not so bad that it is loud or severely impacts performance it is easy for them to just say that is how it is in AUTO. But dangit it isn't, as someone else mentioned it should drive and feel approximately the same whether it is in AUTO or 2WD.

 

[jepaul2198]

If you had the well known lifter/collapsed lifter issue, that issue is resolved by removing the heads, inspecting and repairing as needed the valve train, the pushrods, and the lifters; as well as the cam; if needed.
Sounds like that was accomplished -- that is an engine issue.
If that issue were still happening; you would notice it in idle (Transmission in park or neutral) and while driving (transmission in Drive or Reverse or any of the manual forward gears).

You describe an issue that only manifests itself when you have the transfer case set to "Auto" and you are moving.
Thus, the conclusion is you have a driveline issue.
What you don't mention is whether you have a 2 speed transfer case or a single speed (ie, do you have, 4High, and 2High, Auto4Lo, or do you only have 2High, Auto and 4 High?)

Regardless...if you can demo this issue to a competent service advisor/tech, and demo that it goes away when in 2High, then that same competent service tech should be able to diagnose.

Your powertrain (engine, transmission, transfer case) are covered under the powertrain warranty to 5yrs, 60k miles...so rest easy.

I can tell you, I have a Denali w/ the 2 speed transfer case, and I can hardly detect a difference in the vehicle between being in 2 High and Auto...and given the winter we have had, I have had it in Auto quite a bit. It's smooth as butter.

For some more details on how this transfer case works, suggest doing a little google search for GM Autotrak transfer case. Here is one article.

How Does 4WD Auto Work? Unveiling The Mystery Behind The Technology! - 4-Wheel Drive Guide

How Does 4-Wheel Drive Auto Work? 4-A EXPLAINED. 4WD auto functions by sending power only to the rear wheels until traction is lost. It engages the front wheels by activating an electric motor mounted on the transfer case which engages a metal fork that applies pressure to a set of friction...

4wheeldriveguide.com

Net, you need to find a dealer who is willing to listen; tell them to drive a pickup or full size SUV from the lot and see if it does the same thing...it should not.

You could have issue w/ CV Joint, TransferCase, Hubs, Transmission (although I doubt it, since it doesn't do it in 2WD), Front Drive Axle, etc...
Stick to your guns, regardless of whether they say you should or should not be driving in Auto, the vehicle in Auto does not tend to bind up, make noises, etc.
If you put it in 4hi, and drive on dry pavement, you could get some of what you are saying <--- don't do this.

Thank you very much for the detailed response. Note: I have 2 speed transfer case, 2WD, 4WD, Auto, 4 Lo. You've given me some great talking point and they are much appreciated.

Its worth nothing a separate post was made 6 days ago with almost identical issues. https://www.tahoeyukonforum.com/threads/4wd-auto-problem.139109/

 

[R32driver]

Having owned a 2011 suburban for 8 years and now our '21 yukon for 1.5 years I can say for sure these vehicles do not drive the same in AUTO as they do in 2WD. There is a noticeable difference in feel and noise level when these are in AUTO, its like more rolling resistance and some added drivetrain noise. It's not major but the difference is definitely there. 2wd is super smooth always, AUTO is not. I'm not saying yours doesn't have a weird issue going on but in AUTO mode it will never drive the same as it does in 2wd.

 

[DuraYuk]

I don't think you understand what AUTO does. If you are driving in Auto on dry roads just for the hell of it you are prematurely wearing things out. The reason it was smooth before and not now is because you wore some things out a little.

You just noticed after the repair. But the repair should have nothing to do with what your feeling.

When I worked as a heavy line tech for GM we saw many driveline issues from people driving on dry pavement with it set to AUTO.

The owners manual specifies when it should be used and dry conditions isn't one of them.

Good luck.

 

[mb1500]

Find a long stretch of straight road and switch to 4wdHI and see if the issue is still there. Make sure to go back to 2wd or AUTO before making any sort of turn if you’re on dry pavement.

 

[B-train]

Having owned a 2011 suburban for 8 years and now our '21 yukon for 1.5 years I can say for sure these vehicles do not drive the same in AUTO as they do in 2WD. There is a noticeable difference in feel and noise level when these are in AUTO, its like more rolling resistance and some added drivetrain noise. It's not major but the difference is definitely there. 2wd is super smooth always, AUTO is not. I'm not saying yours doesn't have a weird issue going on but in AUTO mode it will never drive the same as it does in 2wd.

Agreed. In all the GM vehicles I've had with the AUTO option, there was/is more drivetrain noise as well as more rolling resistance.

AUTO locks the front dif into 4wd mode and allows the front and rear tires to rotate differently than each other until a threshold of slip is detected. Then the clutches in the TC engage the front driveshaft and send power to the front wheels.

There is no need to use AUTO unless you have a mix of slippery surfaces to traverse. With the stabilitrac system, 2wd will get you just about anywhere without a spin out. Traction control on the other hand is a completely useless feature that will get you stuck more often than not. I would suggest to the OP on familiarizing oneself with the traction control/stabilitrac disable feature should you need actual wheel speed/spin to get put of a stuck situation.

I always laugh when I see a newer 4wd or AWD vehicle in the ditch and the driver waiting for a tow when they could easily press the GO pedal with the idiot monitor turned off and get on with their day. Keep the tires spinning and they will clean themselves and look for new stuff to grip.