There has been mention of MDS in a number of threads but I thought this subject deserves its own thread to make research easier. I will collate some of the info from other posts. I hope no one minds.
From the Magnum Glossy.
Multi-Displacement System:
1. Four solonoids stop oil flow to unique lifters that prevents intake and exhaust valves from opening.
2. With the valves closed trapped exhaust gases in the cylinder are under high preasure acting as an extremely effiecient compressible air spring.
3. Two cylinders on each bank are always active in 4 cylinder mode (every other cylinder)

MDS could be contributing to an annoying hesitation. se SCHMISL's "Hesitation in the Hemi" thread

originally from kra: Don't forget that the MDS can only work for six minutes at a time. The engine will revert back to 8 cylinder mode to maintain correct temperatures. Once the temperature requirement is met, the MDS will kick in again if driviing conditions merit.

 

Originally from MagnumRT: As I have stated elsewhere on this forum, it would be cool to have a dash light to indicate if it is in 4 / 8 mode. Also an override switch would be nice, for mountain driving or hauling a trailer.

The light should be a simple mod. A relay activated by the same signal that controls the lifter solonoids could easily be wired in to light a dash light. Hopefully the relay will minimize the additiional load on the signal and not cause any problems.

Disbabling MDS might be possible by interupting the signal to the lifter solonoids and running them through a switch. However,disabling MDS may not be that simple since this method could set codes in the computer.

 

I wonder about the long term maintenance and longevity of the MDS. I'm assuming that it will always be the same cylinders deactivated.
From the tuning aspect this means that 4 injectors will be used more than the other four. Will this be enough to make a signifcant difference over time? Will it be a good idea to switch the injectors around every 20k miles or so?

 

I was wondering, since everything on this car is controlled or monitored by a Computer, do the Cylinders alternate from shutting down. Ex: 1, 3, 5 & 7... Then after auto shut down for Temperature, the other Cylinders shut down. Ex. 2, 4, 6 & 8 If it does not work like this, why?

 

Only cylinders 1,4,6 and 7 are MDS cylinders. They do not alternate. This is the best working example of multi displacement engine ever used, it also the 1st time that only 4 cylinders were affected. Ususally all 8 cyl are alternated as needed. Maybe DCX knows something everybody doesn't.

Jerry, fuel injectors have a lifespan of around 200K or so, maybe the MDS injectors will go 300K or so and the others will only go 200K. If you really want to go through the trouble swapping injectors I guess you could. The danger of tearing/losign an oring and causing a fire are far worse than 4 injectors wearing before the other 4. I have never in my career had to replace all the injectors on an engine at the same time for wear and tear.

 

" I wonder about the long term maintenance and longevity of the MDS."
One of the reason I got an SXT.

Merry Christmas - Also I am no longer politically correct.

mike