as stated yesterday i tried pappy's method and all went well.still avg 20mpg when i got home from work last night.i did notice that the mds did not go to 4cyl mode as often which is fine by me.the erratic shifting pretty much is gone.i did install a superchips 3815 today so we will see if that effects anything.will post again as soon as todays drive is over.i programmed for the 87oct tune til i burn this tank up then will change to the 91oct tune.

 

Yea i would like to hear the results of the superchips 3815 installed...im thinking about the same mod for my truck. Im hopingit will push my mds engagement further up the rpm band...its still around1200-1500 rpm.

 

Howdy yall. When MDS is engaged, the RPMs will be HIGHER than when running on all 8 slugs. The revs are higher inorder to keep less of a load on the engine while running on 4 cylinders, thus reducing the risk of detonation. Listen and watch the tach while on the freeway. Put the trans out of overdrive then put it back into od while cruising at 65 mph. Watch, more than likely a second or two after putting the od back on, you will see the revs slightly rise and the sound of the motor and exhaust will change. On my 06, I would cruise at 1800 or thereabouts with MDS off at 65 and 1950 or 2000 with it on. Cruising stedily at 45 mph, revs would be 1400 rpm or so in top gear, MDS off, but 1600 or so wth MDS engaged.

IMHO, the dealer is full of crap when they state that the aftermarket exahust is affecting the situation. Sure exhaust backflow is decreased, but only enough to drop torque 5 ft/lbs tops, not enough to send the trans into convulsions. They seem rather uneducated. I quite frankly believe that you are noticing MDS engaging and disengaging more with the more pronounced exhaust. If it was the trans, more than likely the difference in revs would be somwhat higher, maybe 500 rpms. Remember, besides being controlled by oil distribution and collaspable lifters, MDS is also electronically controlled using algorthyms. Throttle imput is a big part, as any more than 10 to 15% throttle imput will keep it running on all 8 cylinders.

 

HemiBoss that has been my observation on the MDS also. Now that I have a MagnaFlow exhaust its easy to tell when it goes in and out of V4 mode. I also found out that any time you let your foot off the gas it returns to V8 mode. Then the process starts over again. I'm having a little fun playing with it. I'm also a beta tester for the Edge programmer and it shows me when its in V8 or V4.

 

I understand all that...what im trying to get info on is...should it engage into 4 cylinder mode at any speed for example 5-10 mph with light throttle....i thought this system was suppose to engage at cruise speed....50-60 mph....mine seems to engage at any speed...soon as i pull into a parking lot and ease through i feel and here it engage and its at a speed that it kind of bogs the engine down slightly. I WANT TO KNOW IS THIS COMMON.

 

Iceman344, My truck deffinatly does not go into 4 cylinder at low speeds (5-10mph). You may have totally isolated problem. Sorry we got away from your initial question.

 

my truck does the same if I am just tooling around ina parking lot.

 

In short, yes, if the load on the motor is not significant. If less than 10 to 15% throttle pressure is being applied, then chances are that MDS will engage. This is true only if on flat ground or not ascending a hill or grade. Its perfectly fine and does not hurt a thing. These 5.7's with MDS were tested for the equivalent of 300,000 miles with radically different heat cycling methods, engaging and disengaging the cylinder deactivation setup. There was no ill affects on any components from the on and off nature of the setup.

The only real reason that I can think of to shut the system off if needed is the possibility that some may not like the 4 cylinder sound that is emmitted from aftermarket exhaust.

 

HemiBoss, you talk like you have a good working knowledge of the Hemi MDS system. You in that line of Business?

I think most of the guys here with MDS just don't like the way the V4 sounds with an aftermarket exhaust system. I have the MagnaFlow SI/SO cat back. I left the front resonator on the keep the drone/noise down. That works for me. It does sound a little like an exhaust brake when in the V4 mode but it is not loud at all. Put you foot in it and it comes to life with a good exhaust note.