Do I have an Mds Issue?

hello everyone just wordering if i have an issue with my mds it seems that i cannot keep it in mds at highway speed unless im on a slight downgrade i have a 3.92axle and 17" inch rims at 60mph and no wind i can sometime get it to stay in but even the slightest breath of wind or slight uphill (and i mean slight) its out. At 70 mph it will not go in unless im going downhill.

At those speeds the engine has to work hard to keep the speed your going against the air resistance that is being created. So any slight uphill grade or increase in wind makes the truck work hard enough to maintain speed to kick it out of MDS.

^^Lol sounds like you joind the 11-12 mpg club

But ya what they said

I had the same issue with mine, constantly kicking in and out at the slightest change. Plus with the exhaust, it sounded like crap when the mds did kick in. Because of those two things, I got superchips and disabled it.

Couple things to consider:

1. What are "highway speeds" ? Could be anywhere between 55 and 75 MPH which is a big difference. The MDS will run more frequently at 55 than 75.
2. How many miles on the truck? I had a few Hemis with MDS (2 Chargers and a Ram 1500) and found the more miles on the ODO, the more the MDS ran.

The rule of thumb I remember learning was that MDS operates at 20% or less of throttle.

lol ya i guess im actually getting about 14 right now thankyou all for ur reply's just wanted to see if my truck is in line with everyone else sometimes i see a post from ppl saying there doin 70 in mds or there getting 29mpg just makes me wonder if theres something wrong with mine lol

i got 2400km on it now thats about 1700 mile i think but dont quote me i usually drive about 65mph\108km\h

PostalTwo said:

lol ya i guess im actually getting about 14 right now thankyou all for ur reply's just wanted to see if my truck is in line with everyone else sometimes i see a post from ppl saying there doin 70 in mds or there getting 29mpg just makes me wonder if theres something wrong with mine lol

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Yeah - I'm not convinced those guys are entirely accurate when they say that.

I get 26-29 going about 45mph. Other than that, I'm super happy with 18-20 at highway speeds.

So I saw Chaney said mileage with it off averages better than on... Are they a few other people out there who can corroborate this information so we can make it a more accurate statistical analysis? lol

Your biggest issue is the 3.92 gears with the 17" wheels which is making you run higher rpm than a ram with 20" wheels with the same gears and same speed, so you're not in the sweet spot for mds as much

Chaney said:

^ I noticed that upgrading from my 3.55s MDS never comes on at any cruising speeds really anymore... It comes on all the time (If I don't have it turned off) from 30-55 no problem and stays on. How ever driving that speed in texas you will get run over I'm sure you know

So I can see what your saying.

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Haha that's for sure. Some days around here 85 in a 60 will get you run over. There's some days I'm coming home from class cruising at 80 and I get two cars on my ass, get over and they go flying by so I say screw it and follow them at like 95 lol. My R/T could have mds kick in at around 70-75 and 80 on a slight decline but that truck is lighter too. This truck I'm not too sure

Mine kicks in all the time I do have it disabled below 50 as I hate it in town and in traffic on the freeway.

My MDS kicks in very randomly, just under 4kmi on my truck so far, seems to be kicking in less and less now. Maybe the fairly sudden dropping change in temp in my area has an effect on the air/fuel ratio and the way its being consumed needs the mds less or more now? Over the summer seemed to kick in a lot and in the past two weeks upstate NY has gone from 65 degrees to 35-50 degrees. I noticed my mpg was much higher two weeks ago. probably 2mpg's or more. I have 3.92's with 20" wheels and stock tires.

garner said:

Your biggest issue is the 3.92 gears with the 17" wheels which is making you run higher rpm than a ram with 20" wheels with the same gears and same speed, so you're not in the sweet spot for mds as much

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I doubt that matters? I have 3.92's with 20" wheels, but the tire size should keep the gear ratio the same, the wheel size doesnt affect the gear ratio if the tire sizes differ making the tallness of tires the same between a truck with 17" wheels and another with 20" It ultimately boils down to gear ratio and overall wheel/tire size not just wheel.

Easy example a 35x12.5x20 may be the same as a 315x65x17...its in the sidewall of the tire not necesarily the wheel size.

Now plus side for your post against mine, is i have no idea if the stock tire sizes make up for or go along with the wheel size on the new rams. Meaning if the dodges with 17" wheels come with a (just for example) 265x60x17 and the 20" wheels come with a 285x75x20 then the 20" wheeled truck will have a taller tire making the gear ratio less even if both vehicles have 3.92's.

As most of you I'm sure already know, first number is width, second is sidewall and third is wheel size in metric measurement; and in standard like the 35x12.5x20, the first is overall height second is width and third is wheel diameter.

smiley3303 said:

Mine kicks in all the time I do have it disabled below 50 as I hate it in town and in traffic on the freeway.

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How do you disable/program mds, need a tuner/programmer or can this be done from vehicle controls?

How do you disable/program mds, need a tuner/programmer or can this be done from vehicle controls?[/QUOTE]

Manually downshift into 5th or 6th and the mds will not come on

yes using tow\haul mode or shifting at least to sixth

i noticed shifting on your own will shut it off... I've also noticed the manual shifting doesn't really work very well. Truck still pretty much does whatever it wants lol

I doubt that matters? I have 3.92's with 20" wheels, but the tire size should keep the gear ratio the same, the wheel size doesnt affect the gear ratio if the tire sizes differ making the tallness of tires the same between a truck with 17" wheels and another with 20" It ultimately boils down to gear ratio and overall wheel/tire size not just wheel. {quote}

IT matters my tires are 1" shorter diameter so im at 1750-1800rpm at 60mph where ur prob close to 1500rpm's

17" wheels come with a tire which is about a 31", 20" wheels have about 33" tires
Why they don't put a 285/70/17 on stock, idk!

paulycoppola5 said:

i noticed shifting on your own will shut it off... I've also noticed the manual shifting doesn't really work very well. Truck still pretty much does whatever it wants lol

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mine will hold the shift but shifts whens its ready to so it dosent happpen right when i hit the button