I'm posting this for a friend so I don't have every little piece of info so I apologize for that. He's at the end of his rope with this issue so I hoped someone here had heard of this problem. Truck has 80K on it and started running horribly at all speeds. He had it to a local mechanic who said it's an MDS problem. My buddy goes down there and says he watched as the guy had the valve cover off and with all coil packs unplugged, engine cranking... all valves move up and down. with coil packs connected the minute the engine starts the exhaust and intake valve on just one cylinder stop moving. The assumption is that the MDS is shutting these valves down. It is throwing a code but I dont know which one but I can find out.

He then took it to the dealer thinking hed get bent over and dry humped but at least it would be fixed. they said they have to yank the head and change the lifters in question...They think. They said they aren't even sure if that's the problem. they told him the book calls for 1200 for the job but if they end up having problems getting things apart, like exhaust manifold apart (which I guarantee there will be because he lives in the rust belt) that sounds fishy to me.. I mean.. he doesn't get a refund if the job takes less time than the book calls for, but gets upcharged if it takes longer? that's not the core issue though. It's that after dropping all that cash it still may not be resolved. I'm no mechanic but it bothers me a little that they want to change lifters that clearly operate properly under one set of conditions and not another. Maybe it's because I'm not versed in how the MDS lifters work but hearing all he had to say it sounds like some sort of computer or wiring issue. I don't expect the problem to be miraculously solved on MOPARTS, but alot of you guys drive these trucks and maybe someone has seen this?

My 05 Magnum started running like crap due to MDS,turned out it was a Solenoid,they sit right under the intake and break very easy when trying to pull them.
My car was throwing a code so I knew which one,replaced it and it ran fine.

The PCM controls some solenoids in the eng and the solenoids control a bleed to the lifters. So when it cuts a cylinder out the solenoid lets the lifter bleed right down and keeps the valves closed. Also turns the injector off on the cylinders it shutdowns. So it could be :

1. lifters
2. solenoid
3. wireing between solenoid and PCM
4. or the PCM itself , Ron

My 2007 Ram developed an MDS problem at 56,000 miles. One dealer thought that one of the solenoids was bad and replaced it. The problem came back on the drive home, so I returned to that dealer. Then the idiots thought that maybe the wiring may be to blame since they found rat turds at the back of the intake. They thought that rats may have chewed the wires.
In frustration, I took the truck to the dealer where I had bought the truck. Their store was further away which is why I chose the other dealer first. The second place digged deeper and determined that a faulty lifter was to blame. They found that cylinder #4 MDS lifter had a bent link pin that was supposed to alternate between working normally and switching to MDS mode. Because it was stuck, the truck had a cylinder # 4 misfire code and it ran as if I was trying to accelerate uphill with 3 flat tires: Shaking and stumbling. They pulled the head and replaced the lifter. They had to pull the #4 piston and hone the cylinder due to carbon buildup. New rings, a bearing, gaskets, oil, and MDS lifter plus labor added up to $3700 which was covered under warranty.
The truck now has 181,000 miles and I've had no other problems since.

thank you all for the info, much appreciated!


whats got him head scratching is that the lifters work fine while crankiing and only bleed down when it is actually running.

If you put it in tow the MDS is cut off.
See if it runs bad like that.
How many miles are on the plugs?