My MDS System in my 2011 Ram 1500 5.7 recently has started to rattle a lot and it’s causing some concern. Is there any suggestions as to the possible problem or solution?

 

Are you sure it's the MDS system and not due to broken exhaust manifold studs?

-Rod

 

Rattling stops when I disengage the MDS System

 

Okay, yeah, that would seem like a pretty good indicator that it's the MDS. Fortunately for me, I have not yet had a need to look into the failure modes and symptoms of the MDS yet so I'm not going to be of much help, but I'll certainly be interested in following this thread.

-Rod

 

Doesn't MDS just cut oil pressure to four lifters? I can see how that would induce a rattle..... but, didn't dodge have some method of avoiding that? (no, I am really not as familiar with MDS as some would like. )

 

LMAO......guess no one knows the "S" in MDS = System. Watching everyone basically saying Multi Displacement System System 🤣🤣🤣

Quite the opposite. MDS lifters (cylinders 1, 4, 6 & 7) have specific pins in them. When the system engages the solenoids send oil to the ports that line up with those pins, collapsing the lifter. This is done after a combustion event so that it traps exhaust gas in the cylinder, acting like an air spring. Unlike GM's more complicated and even more problematic DOD, MDS only ever uses the same four cylinders. Occasionally I can feel a vibration, moreso if it's an aftermarket exhaust.

OP, if it doesn't do it when MDS is not engaged then it likely isn't a lifter, at least not the roller bearing portion. Contrary to popular belief (internet), MDS wasn't the issue with these engines or hundreds of thousands of engines prior to 2010 would have had lifter issues. The later engines the MDS is programmed a little more aggressively; my 392 will shift from 4th to 5th gear in MDS and if it engages below 90 mph (the cutoff) it can be made to stay engaged above 90. Without any amplifying info it sounds like it was trying to stay in MDS too hard in relation to the load level. That's when I would normally hear/feel some vibration then it would give up and pop back into normal mode.