Vibration with 4 Cyl/MDS

[meechy6ix0]

Hey all, I saw that there was an old thread about a vibration with MDS, but I wanted to check with if ya’ll have any more input. Specifically with a vibration at very light throttle while MDS is on. During decel, there is that loud boom everyone knows, but is anyone else getting a sound and vibration through the pedal when very slightly accelerating which keeps the MDS still on?

 

[Tank2112]

Think what you are experiencing when MDS engages is normal.
I also can feel a very slight vibration feel and slight exhaust tone difference when 4-cyl mode engages.
I have Magnaflow Street exhaust.
If you have a late 22’ year model or newer, as you’ve probably read before, Off-Road + mode should lock out MDS. As does use of paddle shifters or manual shift mode.

 

[stumblinhorse]

I guess I am lucky, I can’t ever tell when MDS engages. I don’t cruise with the exhaust open or in OR+. But I get no sound or anything on either hemi that have. And mine must be on a a lot, since I get 26 and 20 MPG in my 5.7 and 6.4 respectively. But truly I have never noticed it. Last time out I put up the correct display to see it engage and asked my passengers if they noticed anything. Nothing…

 

[Robr651]

I guess I am lucky, I can’t ever tell when MDS engages. I don’t cruise with the exhaust open or in OR+. But I get no sound or anything on either hemi that have. And mine must be on a a lot, since I get 26 and 20 MPG in my 5.7 and 6.4 respectively. But truly I have never noticed it. Last time out I put up the correct display to see it engage and asked my passengers if they noticed anything. Nothing…

I get 20mpg when I fill up, reset the MPG and drive one block without pressing the gas pedal beyond half way… after that it’s consistently 13.5 mixed driving. I notice a definite change in pitch in the exhaust when it’s in MDS with the exhaust open but I also have a Borla Atak installed.

 

[DCWarGames]

You'll hear the difference when MDS kicks on with the exhaust valves open. Sounds like absolute ass. The vibration your feeling is likely due to the way MDS works. It closes off the exhaust valve and lifters, creating a small air gap that the piston uses to "bounce" just like it would after detonation, so while not producing power in the cylinder the pistons and cams can continue their rotation.

Reminds me that blacksmiths always hit the hammer on the anvil to keep their rhythm going, it's the same in the MDS system. I assume the extra vibration we feel is due to this.

I can confirm on my 24' while in 4cyl mode that I get vibrations under load, while still staying in 4cyl. What you're experiencing is normal MDS Hemi. The only thing I can think of is if there was a lifter failure and it's now making contact with the cams. The vibration could be from them hitting and overtime creating a flat spot on the cams which would cause irregulararities in detonation.

 

[meechy6ix0]

You'll hear the difference when MDS kicks on with the exhaust valves open. Sounds like absolute ass. The vibration your feeling is likely due to the way MDS works. It closes off the exhaust valve and lifters, creating a small air gap that the piston uses to "bounce" just like it would after detonation, so while not producing power in the cylinder the pistons and cams can continue their rotation.

Reminds me that blacksmiths always hit the hammer on the anvil to keep their rhythm going, it's the same in the MDS system. I assume the extra vibration we feel is due to this.

I can confirm on my 24' while in 4cyl mode that I get vibrations under load, while still staying in 4cyl. What you're experiencing is normal MDS Hemi. The only thing I can think of is if there was a lifter failure and it's now making contact with the cams. The vibration could be from them hitting and overtime creating a flat spot on the cams which would cause irregulararities in detonation.

Thanks for the insight. This is my first vehicle with cylinder deactivation so I’m not sure what to expect. What I’m feeling is very slight, mostly through the gas pedal and auditory.

 

[DCWarGames]

Thanks for the insight. This is my first vehicle with cylinder deactivation so I’m not sure what to expect. What I’m feeling is very slight, mostly through the gas pedal and auditory.

You can rest assured that this is normal! Drive in peace, with a giant smile. If you want confirmation that's tangible to your own experience not second-hand, go test drive another 392 or 2 or 3 at the dealer/carmax.

 

[Willhonkforparts]

Yup, 100% normal. It's not just the 392 either. Most V8 vehicles which drop to 4cyl at low load suffer from this. Sounds like garbage and producing a different frequency of vibration that is noticeable. Heck, my 2007 Chev Avalanche had this same issue.