Getting vibration when AFM is active.

[Adrian92]

Hello everyone, before anything, thank you for taking your time to look at my post and chiming in. Truck is a 2010 Tahoe 5.3L PPV with 188k miles.

As the tittle says, i am getting a vibration whenever my truck has the AFM active. I keep my cluster in the “Instant Econ V4/V8” mode. I’ve been monitoring this for the past week or so. Between the speeds of 30-55mph when the V4 mode is on, i feel a vibration on my gas pedal and steering wheel. But between the speeds of 60mph+ the vibration on the pedal is faint but the steering wheel is the same. However, the moment i tap the gas pedal even in the slightest, that the V8 mode kicks in, all vibration goes away. I have no check engines, no performance issues, no misfires, fluids and oils are perfect, nothing.

This is not something that seriously bothers me like at all, i am just curious what could be causing this and if anyone else has encountered this and found what the cause was. I do have a 2008 and 2016 Yukon XL both 5.3L too and the AFM don’t vibrate like mines does when ON. Looking up online the one thing that comes up the most is motor mounts, but in my experience with bad motor mounts, this doesn’t feel like it’s that, especially since is only when im driving and when im stopped at a light or at idle, there’s no vibration coming from the engine or anything, no kicks either, but i could be wrong. I also know my car is a PPV vehicle so i am not sure if this is also normal. Any opinions/suggestions are appreciated!

 

[Foggy]

Probably the torque converter clutch locking/unlocking and they are known
to go bad in stock configuration by about 110K
You can get some of that tuned out with a reputable tuner who can
turn off the DOD AND make some changes to your transmissions shift tables
and lock up tables that will make your 6L80E SO much more enjoyable to drive
The torque converter "may" already be worn: it throws its clutch material thru
the entire trans requiring a full rebuild if not replaced as preventative maint.

You also could just have vibrations due to needing standard prev maint:
Plugs, wires, Clean TB, Clean MAF, Air filter, dirty engine oil ... etc

 

[tom3]

Our 2019 is also starting to do this but just slightly, 33k miles. When new I couldn't tell it was in 4 or 8 cyl. mode without actually looking at the DIC. I've read that when in 4 cyl. mode those cylinders will run almost at full throttle until the V8 mode comes back on. Can't be good on those parts I think. I'm pretty much living with it until the extended warranty runs out.

 

[j91z28d1]

while it might be normal, afm in general is a failure waiting to happen. I would have to turned off in the ecm as soon as possible.

 

[Marky Dissod]

Our 2019 is also starting to do this but just slightly, 33k miles. When new I couldn't tell it was in 4 or 8 cyl. mode without actually looking at the DIC.
I've read that when in 4 cyl. mode those cylinders will run almost at full throttle until the V8 mode comes back on. Can't be good on those parts I think.
I'm pretty much living with it until the extended warranty runs out.

When in Engine 1/2@$$ - when the ecm decides that 4 cylinders is better than 8 -
the throttle blade does open further than it would if all 8 cylinders were sharing the work equally.
IN THEORY, the wider the throttle is open, the better the BSFC. Whether or not this is true,
in practice, there are several sacrifices made that erase this benefit over time for the end user.

Think about this. Prior to Engine 1/2@$$, all 8 cylinders always worked together equally.
When in Engine 1/2@$$, 4 part time cylinders take a break and cool off,
while the full time 4 cylinders work even harder than when all 8 are working equally together.
Think about this long enough, you'll disable Engine 1/2@$$ mode at your first opportunity.
HINT: why were early Hemis with Engine 1/2@$$ cracking blocks?

The vibration you're feeling is the torque converter clutch wearing out.
GM locks the TCC differently in V8 mode vs V4 mode (PulseWidth Modulation I think)
so that no one inside the vehicle feels or notices V4 mode.
But the TCC pays for this, and when it finishes wearing out, it takes out the rest of the 6L80 with it.

6L90s which are never coupled to engines with V4 mode tend to last longer than 6L80s.
Hopefully your extended warranty covers your 6L80.