2021 6.2 Sierra 1500 Denali rough idle and engine vibration at ~1500 rpm

[Rob Spector]

Good morning,

I know the rough idle topic has been well discussed here but I have yet to see a resolution or even someone who had the motor mounts done fixing the problem. When my truck is completely warmed up after driving for 10 minutes at idle in park or in drive it misses pretty bad. You can see the engine vibrating and can really feel it through the seat and floor. Lately, after fully warmed up there is a vibration that can be felt through the steering wheel and center console at around 1500 rpm, like what you feel on a 4 cylinder motorcycle at certain RPM. It isn't severe but on long trips on the highway it gets pretty annoying. I have an appointment scheduled for next week and was wondering if anyone had any insight I can share with the dealer when I drop it off. It seems to get significantly worse when the gas tank is near empty, but that may just be me or there is less mass there to absorb vibration.

 

I use 93 octane fuel

Truck has 10k on it

Fuel trims at 1500 RPM are near zero. Short term stays around +- 5% long term is a bit lower.

No codes

Fuel pressure at idle is between 20 and 40 psi

Rail pressure is much higher between 600 and 2k depending on throttle application.

 

Any suggestions?

Thank you

Rob

[GMCustomerService]

On 9/2/2022 at 10:57 AM, Rob Spector said:

Good morning,

I know the rough idle topic has been well discussed here but I have yet to see a resolution or even someone who had the motor mounts done fixing the problem. When my truck is completely warmed up after driving for 10 minutes at idle in park or in drive it misses pretty bad. You can see the engine vibrating and can really feel it through the seat and floor. Lately, after fully warmed up there is a vibration that can be felt through the steering wheel and center console at around 1500 rpm, like what you feel on a 4 cylinder motorcycle at certain RPM. It isn't severe but on long trips on the highway it gets pretty annoying. I have an appointment scheduled for next week and was wondering if anyone had any insight I can share with the dealer when I drop it off. It seems to get significantly worse when the gas tank is near empty, but that may just be me or there is less mass there to absorb vibration.

 

I use 93 octane fuel

Truck has 10k on it

Fuel trims at 1500 RPM are near zero. Short term stays around +- 5% long term is a bit lower.

No codes

Fuel pressure at idle is between 20 and 40 psi

Rail pressure is much higher between 600 and 2k depending on throttle application.

 

Any suggestions?

Thank you

Rob

This is certainly not what we like to hear, Rob Spector.  Please know, customer satisfaction is extremely important to us. Our team would be more than happy to take a closer look into the concerns with your truck. To do so, please send an email to [email protected] with ATTN: Rob Spector/GM Trucks in the subject line.

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[Denali Driver]

Hello,

Could your concern be the dynamic fuel management deactivating cylinders? I have a 2019 5.3ltr Denali 1500 and i noticed more so lately with a sort of like hesitation or vibration at highway speeds. Can also see the tachometer fluttering @ 1500 rpm. Also recently, yesterday as a matter of fact replaced all 8 spark plugs because i had an ignition alarm code come upon cylinder # 8. The spark plug was fouled badly. Tested my truck today and it felt a little better.

I  also have a burning oil concern on my truck average 1 quart / 1000 kms.

[Rob Spector]

Well, unfortunately the GMC dealer treated me exactly how I figured they would, no codes, no problems.. I brought it back yesterday as I was driving by and the engine was really rough that day, the "head truck tech" came out with his scan tool, told me no codes, no problem, they all idle rough, its valve overlap due to AFM.. At the same time a heat shield was rattling because the clip came loose (due to the engine vibrating). So now I don't know what to do, I've had it in 4 times and 4 times they tell me that they don't see a problem, even when they are watching the engine miss... They have not done the test with the Pico for vibration and don't intend to with no codes. Its a sad day when you can't get a dealer ship to troubleshoot anything past plugging it in.

[AvgJoe]

2021 AT4 with 6.2l and I also have the shimmey and vibrations when idling. I have 40,000 miles on it and it has done it since I purchase it a year ago. Got extended warranty and everything and yes, no codes = no service apparently. I can’t understand how they can turn them away knowing something isn’t as advertised. I feel like GM needs to write this as a disclaimer on the sticker

 

Attn: most likely to shake and vibrate when new, but it’s perfectly fine and still charge $70,000 for the truck and see what sales look like. Love my truck. This is the 2nd GMC truck I’ve owned and I’ve had the dynamic fuel managemEnt turned off since I bought it. I def feel like it’s the motor mounts yet they won’t throw a code. Tough to force a dealer to honor their “Certified” bumper to bumper when there is no code for them. It’s BS is what it is.