MDS Noise / Vibration - engine and trans mounts ? exhaust ?

[MarineBSP]

My apologies if the answers to my question(s) are out there and my searches missed them.

My 2018 RAM 5.7L has 134K miles, and over the past 7 to 10 days I have been noticing a new growl or rumble and a subtle vibration in the driver seat when MDS 4-cylinder mode engages under load. It doesn't do this if in a downhill coast - only on the flat or slight uphill. The rumble stops the instant the engine goes back to all eight cylinders.

I'm suspecting worn/hardened mounts on engine or transmission that no longer isolate the coarser 4-cylinder mode vibrations. It's definitely not valvetrain related. Could be exhaust hangers or positioning. Any other thoughts ?? I don't think my truck has a diverter valve in the exhaust that triggers with 4-cylinder mode - I know some manufacturers do that, but I've never seen any mention of one on our HEMI's.

I'm hoping someone with similar truck and miles has already experienced this and fixed it.

Thanks for ideas and simplest things to check first.

 

[Daw14]

Have you put new plugs in it ever ? 100,000 miles recommended.

 

[Mojo88]

A lot of folks would call this perfectly normal behavior for MDS system. I have 2019 5.7L and the MDS (with symptoms like yours) drove me nuts, so I turned it off using the gear selector on the steering wheel each time I got in, and eventually turned it off permanently in the tune.

I like the idea from @Daw14 above, maybe new plugs. Maybe try some super-duper fuel injector cleaner too. Possibly some sludge buildup in oil, or lifter wear, affecting the MDS valvetrain operation.

 

[Sherman Bird]

A lot of folks would call this perfectly normal behavior for MDS system. I have 2019 5.7L and the MDS (with symptoms like yours) drove me nuts, so I turned it off using the gear selector on the steering wheel each time I got in, and eventually turned it off permanently in the tune.

I like the idea from @Daw14 above, maybe new plugs. Maybe try some super-duper fuel injector cleaner too. Possibly some sludge buildup in oil, or lifter wear, affecting the MDS valvetrain operation.

If the strategy is akin to GM's, the Torque converter turns on at ridiculous low speed for "CAFE"... yeah! Brilliant, eh? NOPE! Make sure the trans fluid isn't overdue for a change.

 

[joesstripclub]

Mine will on occasion make a terrible sounding noise the first time it engages in the morning. Not sure if its cold oil or something else that causes it. Doesnt do it again so I haven't decided to worry too much about it yet.

 

[MarineBSP]

Plugs were replaced at 73K miles (NGK Iridium) - probably do again this Spring or Summer. Transmission pan and new Mopar fluid at 93K miles (a 2X drain & fill - estd ca. 75% new fluid).

I know some owners seem to have noise/vibration like this from nearly new, but this has only become an item for me in the past two weeks or so. As I have time, I'll be checking exhaust and engine/trans mounts. I will update this thread with my findings.

 

[haleme]

@MarineBSP Curious what you found. I have the exact same noise on my 2018 2500 6.4, but it sounds like it is coming from the passenger side near the rear of the cab. It started around 80K and the dealer re-flashed the MDS module to resolve. It worked for about 2 weeks.
Now that the truck has 95K, the noise is happening off idle acceleration in addition to MDS load. I replaced the spark plugs this afternoon to see if that would resolve the issue. While it is significantly better, the vibration persist, but not all the time.

 

[haleme]

I think I figured out my vibration. The intermediate pipe to muffler clamp is loose. I was able to push up on the muffler this afternoon and could see the pipes rotation on each other. The muffler has also pulled out about 1/2" from the intermediate pipe.
The clamp has rusted pretty badly, so it may need to be sawed off, but I am hopeful this will resolve the vibration.

 

[haleme]

I love being right. The loose exhaust connection was causing the rattle when MDS engaged. New clamp and the problem is solved.

2500 Exhaust Rattle