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Discussion Starter #1
There is likely already a thread on this subject but a quick search didn't turn up anything specific:

I've taken a number of longer trips now in our 5.7 Hemi Commander (200+ highway miles) and this has provided some opportunity to observe the MDS system in action. One thing I've noticed is that it seems unbelievably conservative. The slightest perceivable incline (and even some imperceptible ones) result in the MDS kicking off or not engaging, and anything other than the absolutely lightest throttle application on a completely level or downhill road will result in it not operating.

I assume this is typical, but it seems like common sense would dictate that the programmers could have been just a tinge more liberal with the conditions under which it would activate. However, I do admit that all of this is just armchair engineering speculation, of course.
 

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That seems to be the same I am seeing. Looks pretty worthless to me. I also noticed a change in gearing taking place along with this. With the cruise set, the tach would jump a little, maybe a 150rpm, perhaps the torque converter is unlocking. And this is all taking place with almost no noticable grade increase, running at 70mph on cruise.

Another thing I notice in the gearing is that it does not shift into the last gear till about 64mph. That seems a little high, not sure why.
But at 13.5mpg average, there is certainly room for improvment.
 

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Discussion Starter #3
Do we have a lockup torque converter?

If I reset the mpg meter before a trip I can average almost 16 mpg with a light foot. Now I wonder what it would be without the MDS. Is there any way to purposely deactivate it for a trip?

My understanding is that the MDS systems in new cars are only going to provide about a 15% increase in gas mileage. If you were going to get 14 highway, then I guess the MDS wouldn't rock your world with improvements.
 

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That seems to be the same I am seeing. Looks pretty worthless to me. I also noticed a change in gearing taking place along with this. With the cruise set, the tach would jump a little, maybe a 150rpm, perhaps the torque converter is unlocking. And this is all taking place with almost no noticable grade increase, running at 70mph on cruise.
The MDS does not operate at 70 mph.
 

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I could have sworn it has come on above 70 mph before.
Nope. This is from the Jeep website and is for the 2009 model which has a wider MDS operating range than the previous years.

The 5.7L HEMI® V8 engine features the economical Multi-Displacement System (MDS), which deactivates four cylinders when eight are not needed. When cruising at highway speeds between 40 and 60 mph, MDS uses advanced computer technology and electronic throttle control to transform the HEMI® V8 seamlessly from V8 power to an efficient four-cylinder powerplant in 0.04 seconds.
 

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Discussion Starter #7
On a highway trip, I spend about 99% of my time above 60mph, as does everyone else. That's preposterous. That way it's designed now, it'll only activate when I'm in a slowdown and not accelerating.
 

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Nope. This is from the Jeep website and is for the 2009 model which has a wider operating range than the previous years.

The 5.7L HEMI® V8 engine features the economical Multi-Displacement System (MDS), which deactivates four cylinders when eight are not needed. When cruising at highway speeds between 40 and 60 mph, MDS uses advanced computer technology and electronic throttle control to transform the HEMI® V8 seamlessly from V8 power to an efficient four-cylinder powerplant in 0.04 seconds.
Well mine was sure showing the fuel saving mode at 70mph, off and on. What is the point at 60mph when it has not even shifted into high gear?
Maybe that is why if does not shift into high until 64. Does not make sense to me.
 

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Discussion Starter #9
Maybe the 40-60 mph thing is the sweet spot. I did notice that it came on far fewer times at 70 and above.
 

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I LOVE the MDS ... I do a lot of hiway travle (I did a job that was a 400 mile round trip last Tuesday) and I got a solid 21 to 22 MPG (normal American gallons) on the hiway.

The trick is to drive slower :) and do NOT touch the gas or breaks ... you have to set the cruise at 55 to make it work .. to me that's amazing to get 20 MPG with a 350 hp engin!
 

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I am simply not patient enough to cruise at 55 for a 400 mile drive, let alone have the tolerance to deal with all the people who would speed angrily past me on the NJ Turnpike. If I did, I imagine it might be possible to get up to the numbers you mention.
 

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Has anyone done the LED indicator MOD?????

... I remember seeing it here ... you can tap into a certian wire on the harness and it will go ON when the MDS is operating in 4 cyl.

This is on my list of MODS to do once summer finaly gets here
 

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Discussion Starter #14
ECU update.

I wonder if older model years will be able to flash the system so that we can get a wider range MDS similar to the new models.
 

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I am simply not patient enough to cruise at 55 for a 400 mile drive, let alone have the tolerance to deal with all the people who would speed angrily past me on the NJ Turnpike. If I did, I imagine it might be possible to get up to the numbers you mention.

There you go :) ... I can have the patiance becasue it's so AWSOME drving the Commander :) after SOO many years of driving crappy tiny cars.

Also I get paid based on the job and how far away it is not how much gas I use ... so if I save gas? .. that money goes in my pocket ! :)

I'm also in northern Ontario up here ... once you get out of Toronto there's basicly no traffic ... I can play Yatzee on my phone, do emails and text messages, crank the tunes up .. and I'm there before I know it!
 

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I wonder if older model years will be able to flash the system so that we can get a wider range MDS similar to the new models.
That's a good idea ... maybe someone has come up with a hack .. far as that goes .. there could be a hard wire hack?? ... a wire to tap into along the line of the indicator light? ....... and add a toggle switch you could put on the dash for long trips?
 

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I know for a fact that mine was working when I locked in the CC at 65 mph.
 

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I have the 08 and it has an indicator for the MDS... Mine, does indeed, activate between 40 and 60 mph, but, that is for activation. I've even had it activate at 35 mph, but, very rarely. It remains active at all speeds above 60. I've had mine active at 75 and better.
 

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I'm with webslave. I often engage the cruise control at 31 mph in my neighborhood to prevent getting a speeding ticket and I continually see the "Economy" status come up on the dash. Now... I've got other issues with the smoothness of the MDS kicking in. A noticeable surge can be felt as it goes from 8 to 4 cylinder mode. Going to mid-grade gas helps a bit, and premium a bit more to where at least it's not annoying. But is there a flash or something common to the '08s that make it "less" smooth that other MYs?
 
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