[elboricua75]

I have been reading alot about the new 5.7L HEMI with MDS technology but they never say which 4 cylinders shut down. does anyone know which 4 cylinders shut down? and is it the same 4 cylinders all the time? or does it rotate to prevent wear and tear?

[CDN R/T]

Can't answer your question but...

I've been driving one for a little over a week now (~2,000kms) and I can say that if you weren't told that cylinders are shutting down, you'd never know. The shutdown / startup is seamless, power on demand. It IS noticable at the pump. I've been playing pretty hard with this thing and still averaging ~12.9L/100km.

Ok... change 'pretty hard' to 'really hard' !!

[Operator]

Yes, the same 4 cylinders are deactivated. As for wear and tear, I guess these first year versions will have to be the guinnea pigs! I'm glad I bought my truck in '04 and didn't wait because now for 2006 the truck hemi gets the MDS also. Not sure I want a first-year example of a system like that.

[Daytrepper]

I saw a demonstration of this at the detroit auto show-- was very interesting it looks like 2 cylinders on each side cut out simultaneously, and work perfectly in conjunction with the others to keep it all in balance-- and it is always the same 4 that do it-- pretty neat idea, cant wait to see them after 100k miles or so though!!

[cobra65]

Well, it's not a new idea....Cadillac had an engine that did the same thing back in the early 80's I believe.....think they called it a 4-6-8 ....they had alot of problems with them though....of course now the technology is much better.

[Spinnaker]

Yeah, General Motors was the first company to install this technology in the first place I believe. Of course now it works much better.

[moparman]

GM wound up replacing the engines after a class-action lawsuit. My wife's uncle had one. What a pos.

[Dkaos1]

my grandfather owned one of those. Because of that he went from being a caddy driver to a lincoln driver. He bitches about that car to this day!!!

[88pdance]

check this out: REMOVAL
Disconnect the negative battery cable.Remove the intake manifold. (Refer to 9 - ENGINE/MANIFOLDS/INTAKE MANIFOLD - REMOVAL). Remove wiring harness connectors from the MDS solenoids. Remove hold down

[wrench]

The cylinders still get the same wear and tear, the only difference is the fuel injector is not supplying fuel and the plug is not sparking. The valve and still moving. With these new 100,000 mile tune ups, I guess they figure you might as well just replace all eight of the plugs, even if they have not fired as much.

[88pdance]

Theory of Operation
When all criteria has been met, power is supplied to each MDS Solenoid when the engine is making a transition from 8 cylinder mode to 4 cylinder mode. By actuating the solenoid, oil pressure is raised to the pair of lifters that coincide with each particular solenoid. The oil pressure pushes in the locking pins that allows the lifter to collapse, decoupling the valves and camshaft

[adaptabl]

The Hemi is a 30,000 mile tune-up engine and has 16 plugs to change with some very expensive wires. The cylinders do not get the same wear since they are not producing any combustion pressure when shut down. Let hope it goes okay for all the first year guinea pigs.

[elboricua75]

HEHE well you have to remember that the HEMI 5.7L uses 2 spark plugs per cylinder so that is 16 spark plugs every time you do a tune up.

[wrench]

Opps, yeah that is it? 16 plugs. As far as the cylinders wearing due to compression, it is not going to be enough to notice unless you have 1,000,000 miles on it. And lets all be serious, when is the last time you have seen a DCX engine with that kind of mileage?

[Operator]

That's one of my pet peves with this engine. In this day and age, they should be ashamed of themselves for putting 30K spark plugs in an all new engine. I'll be changing mine about once a year if I stick with the OEM plugs.