Vibration when in V-4 mode only

[Tylus]

When burning all 8 cylinders she rides smooth as glass.
When in V-4 mode from about 40-60 mph there is a persistent "rumble" or vibration that is present. Feels kind of like driving on a cobblestone road, just not as harsh.

The second the rumble appears, I can blip the throttle so it shifts to V-8 mode, and the rumble/vibration disappears. This is without changing engine RPM or actual speed.

So in my mind that rules out the usual stuff like torque converter, driveshaft, and/or an out of round/balance tire.​

Anyone else? I keep intending to pin that stupid butterfly valve open in the exhaust to see if that's the culprit. It's been squeaking lately and even my wife noticed it finally. there has also been a weird harmonic in the cabin that is very prevalent when the windows are down and the motor is in V-4 mode. Just need to get home before sundown 1 day to get it done.

TIA. Love the Tahoe in all other respects

 

[ccapehartusarmyINF.(ret)]

there is a knownj issues with AFM lifters going bad i guess most people get a tune and turn of AFM mode

 

[Tylus]

what is AFM?

and there is no way in hell I'm going to pay a dime of my money to fix a motor issue. I'm not against tuning my rig for my own fun, but not to fix a screw-up. especially while under warranty

 

[yukontruckman]

what is AFM?

and there is no way in hell I'm going to pay a dime of my money to fix a motor issue. I'm not against tuning my rig for my own fun, but not to fix a screw-up. especially while under warranty

AFM = Active Fuel Management, but that's not your problem.

Sounds like you may have the "buffeting" issue?

Read through this thread and let us know what you think:

http://www.gm-trucks.com/forums/topic/162779-2015-yukon-noise-in-cabin/

 

[Tylus]

yeah I saw several of those threads earlier this year when I first noticed the vibration...and the damn squeak from the butterfly valve.

I'm hoping the problem is more induced by the exhaust valve vs. the inherent roughness of the motor in V-4 mode

it's pretty damn bad though when it happens. When we initally bought the Tahoe I couldn't tell when shifting from V-8 to V-4 mode. Nor was there any defineable difference running down the highway in V-4 mode. Now though, the second it shifts to V-4 mode we hear the audible flutter noise (when windows down), and the damn thing starts rumbling. I'm hoping pinning the valve open helps out.

 

[Tylus]

so over the weekend I bolted the buttefly valve open to stop the damn squeak.

that worked great.

and the roughness while in V-4 mode has gotten pretty damn bad. My wifes Tahoe only has 11,100 miles after 1yr. It's unacceptable for this crap to occur. Especially after I got a letter in the mail, and today a phone call about 4 recalls my Tahoe has outstanding

 

[Deephaven]

Take it into the dealer and take the service manager for a drive. Tell him you want it gone.

 

[Tylus]

Tahoe is at the Dealership right now. They spent all day trying to accomplish 4 recalls on it.

One of the recalls is for the PCM. The Tech tried 5 different times to update the PCM with no success. Apparently you have to wait 1 hour between tries if it isn't successful in flashing the PCM.

Tomorrow they're supposed to troubleshoot the V-4 crap after they get the recalls done.

 

[Mikef]

How did this story end?????

 

[Tylus]

Nada

Chevy refuses to acknowledge my car is doing it. They also can't duplicate my interior lights doing the flashing thing every time you hit brakes or left turn.

Trying to escalate the issue but Chevy keeps stonewalling me and referring to the Dealership...who of course cannot duplicate