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

[jepaul2198]

Hello,

Apologies ahead of time for my first post being what it is. I'll try hard for brevity, but often my posts are long because I do not have time to make them short.

I'm not a mechanic and can barely change al alternator on a 1993 K5 Blazer, I'll do the best I can.

2021 Yukon Denali
Currently 21,000 Miles
The problem first started at 16,000 miles (August 2022)
Magnetic ride and air suspension

Current Issue: After replacing the lifting rods and cam actuator, the vehicle does not drive right in AUTO mode. Prior to lifting rods being replaced when driven in AUTO mode, the car accelerated smoothly with only a hint of the gears changing. It was smooth at slow or fast acceleration. After the lifting rods were replaced, acceleration is bumpy, rough, and hard when set to AUTO mode. It almost feels like it is shifting ten micro shifts in between each real shift. Some of the "bumps" or "feeling" is hard, like pushing a manual speed into gear. But again, none of this is actually gears changing. It feels like it is surging or stuttering between each gear. It is faint, although some are harder than others and indeed hard enough to feel, and it is continuous. At higher speeds, it's almost like going over micro rumble strips, or the tires are out of balance.

After replacing the lifting rods, I took the vehicle to two dealers. When first bringing the car to them, each dealer test-drove the vehicle in AUTO mode and agreed something was wrong. Only after they have had a chance to look at it will they come back and tell me to drive it in 2WD mode. But there was never a problem in AUTO mode before the lifting rods were replaced.

I have also test-driven other 2021 Denalis, even going so far as to rent one, and drove them around to be sure I wasn't imaging things or being a weird OCD-type customer. There is something wrong that wasn't wrong before the lifting rod repair. I feel like the dealers agree there is something wrong when they first drive the vehicle, but when they can't find any codes or warning lights, they don't know what to do, so they come back and tell me, "GMC says to drive it in 2WD mode". But that isn't the point. It never had these issues before the lifting rods were replaced.

Snap Shot – High-level points over a 6-month period and many visits and calls left out. Total drives to different dealers is 9. The total spent on rentals is $2350. Total time so far +6 months.

The vehicle never had any of these problems before the lifting rods were replaced back in August. Only after that service did these problems in AUTO mode start.

 

[Chad G 1979]

When you say AUTO mode, are you talking about the transfer case being set to auto and not 2 high or 4 high? Is there a reason you drive in auto all the time instead of 2 high? From what i have read in the owners manual, auto is supposed to be used when road conditions are variable, say from dry, to snow covered and back, but not necessarily to be used all the time. If you need auto used all the time, then its needed, but i belive it has the transfer case running in a configuration that makes it quicker to change from 2wd to 4wd vs standard 2wd and may be causing some excessive wearor something is damanged in there. Just my thoughts on it.

 

[jepaul2198]

When you say AUTO mode, are you talking about the transfer case being set to auto and not 2 high or 4 high? Is there a reason you drive in auto all the time instead of 2 high? From what i have read in the owners manual, auto is supposed to be used when road conditions are variable, say from dry, to snow covered and back, but not necessarily to be used all the time. If you need auto used all the time, then its needed, but i belive it has the transfer case running in a configuration that makes it quicker to change from 2wd to 4wd vs standard 2wd and may be causing some excessive wearor something is damanged in there. Just my thoughts on it.

Thanks for the reply Chad.

Yes, I'm referring to the setting of AUTO versus 2wd or 4wH. I understand the point you are making with the manual, its the same point the dealer is telling me. But my point is there was never this issue in AUTO mode prior to them replacing the lifting rods. It ran silky in AUTO prior to that work. My wife doesn't want to have to think about putting the car in 4wd or auto when it might start raining or be a little slick in the mornings when she backs out. She wants it just like the land rover we had where she sets it to AUTO and the car decides what it needs to do, not her. (I want the car doing this also and not her) As far as GMC is concerned lets just assume my road conditions are always variable so I need to always drive in AUTO. I would like the car to drive the same way in AUTO as it did before the lifting rods were replaced.

Thanks for the verbiage on transfer case and wear/damage. Gives me some talking points.

 

[Blackcar]

Why where Lifting rods replaced and clarify what a lifting rod is.

 

[jepaul2198]

Why where Lifting rods replaced and clarify what a lifting rod is.

Lifting rod(s) broke on August 8th. I got the vehicle back on August 22nd.

This happened - https://www.tsbsearch.com/Chevrolet/PIP5776C - In my case a rod broke and the vehicle was not driveable. Specifically I was turning into a starbucks parking lot and BAM something happens and a loud knocking starts and the vehicle limps from there.

And this update to the above PIP - chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://gm-techlink.com/wp-content/uploads/2022/05/TAC-Dealer-Monthly-Tips-and-New-Information-May-2022v3.pdf

And then this was done - https://www.tsbsearch.com/GMC/PIP5794B

Important to still note the current issue was not happening before the lifting rods issue. PIP5794 was an attempt by the dealer to fix the current issue but it did not fix it, so now they say just drive it in 2WD.

 

[Stbentoak]

Does the vehicle exhibit the same problems in 2wd? If not, at least your problem is isolated to the drivetrain. If so, it could be a tranny software issue. It should be driven with a monitor hooked up to is to see what the output of the engine and tranny are under load. Who knows what got changed when you were in for this "Lifting rod" issue...

While technically you "can" drive it in auto all the time and nothing should stop you from doing that, it's really pointless and has no benefit ( And possibly some negatives..) Unless your weather conditions truly dictate this... backing out of the driveway or a little rain doesn't dictate Auto. I've drove mine thru blinding rains in 2wd and I'm more concerned about hydroplaning on crappy stock tires than wheel slip on interstates. This vehicle is pretty heavy, and in 2 years of 4 season driving, I've probably had in in auto 2-3 times max.

 

[jepaul2198]

Thanks for your reply ST. It does not have these same symptoms in 2WD.

Of course you are correct that manually switching from 2WD based on conditions is optimal, a smarter man than me can have that conversation with my wife. Who just wants to set it and forget it just like her lovely little Discovery did that I fought to trade in for this because I wanted more room. "We never had to think about when to switch things in the Land Rover", Wife

I just want the vehicle to drive like it did before the liftin rod issue. Regardless of if/when I shoudl have it in 2WD my point with GMC is that the vehicle drove great before, so I would like it to drive like that again. It happened at 16,000 miles, full warranty.

Does the vehicle exhibit the same problems in 2wd? If not, at least your problem is isolated to the drivetrain. If so, it could be a tranny software issue. It should be driven with a monitor hooked up to is to see what the output of the engine and tranny are under load. Who knows what got changed when you were in for this "Lifting rod" issue...

While technically you "can" drive it in auto all the time and nothing should stop you from doing that, it's really pointless and has no benefit ( And possibly some negatives..) Unless your weather conditions truly dictate this... backing out of the driveway or a little rain doesn't dictate Auto. I've drove mine thru blinding rains in 2wd and I'm more concerned about hydroplaning on crappy stock tires than wheel slip on interstates. This vehicle is pretty heavy, and in 2 years of 4 season driving, I've probably had in in auto 2-3 times max.

 

[Stbentoak]

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….

 

[Blackcar]

I would go to different dealer engine should operate same in 2wd as in auto, which is transfer case and not engine operation now in 4-wheel low it will cause transmission to operate differently.

 

[Z15]

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