My '12 Durango R/T has a slight, but noticeable "bump" at speed that can be felt through the seat and floor. It happens about every 5-8 miles, and the tach makes a little fluctuation at the same time. Kinda feels like the A/C compressor cycling, but firmer. It happens with the climate control off or on, with tow button off or on, and it's not the economy mode (cylinder cutout) cycling, as the "eco" indicator remains on. 22000 miles on it. I noticed it before, but have had to start using the car for my new business, so lots of highway driving now, making it more noticeable. I've searched on this forum with no luck. Any ideas?

 

hmmmm, I've had an issue that might be similar but I'd describe it as more of a pulsation, but I could see it as a bump, too. For my truck it's at say 50 - 60 MPH sustained. If I'm cruising at 70+ I don't feel it. I can also make it go away by pulling the truck down to 4th gear if I'm riding at the slower speeds. I've kind of assigned my issue to the vehicle working toward the higher gears too quickly, probably in an attempt to improve fleet mileage. At 50 MPH in "D", RPM's are barely above idle which is really not enough, kind of lugging the motor I guess, especially if there are hills. Any of that sound like your truck?

 

if it was mine i would have the rear axle checked out. the spider gears might be going bad. if it needs work i would put a posi in, in my 2001 dak the factory 8 1/4 calls it powr-lok. i had a dana/spicer locker put in. 84852 , install kit drk303b, 75W90 synthetic gear lube vv975. have been in 30,000 miles, no trouble. best $1600. i ever spent.

 

Just because the ECO light is on does not mean MDS is activated. You need to hook up a scanner and watch it switch between 4-8 cyl mode, you will notice that very small throttle inputs will cause the system to switch back to 8cyl mode (the bump) but your ECO light stays ON untill you increase the throttle marginally or decrease it dropping it back into 4cyl mode. Mine does this (checked with my scanner) and I noticed that if you look really close at the fuel bar it drops by a couple MPG corresponding with the "bump" but the ECO light is still on. It's hard to tell if you haven't driven another MDS Hemi if what your feeling is truly the MDS engagement or another problem. See if you can borrow a scanner or have your dealer diagnose it. You should still be within your powertrain warrant. Good luck bro

 

Fullslp- That may very well be what it is. It's done it since new. You gotta pay attention to feel it, but it's there. Got plenty of warranty left, so I'm not too worried at this time. I also try to drive for the best mileage, and have noticed that the rpm is the same at 55 or 65, but lower at 60, and that's also where the mileage is best, at around 22-23. I have had another MDS Hemi, a '08 Charger R/T, but don't recall the same feel. Maybe my memory is failing...

 

That sounds just like the MDS kicking in. I do wish they corrosponded the ECO light and MDS. That seems pretty logical to me.

 

Hey TOOLZ, was giving this some thought yesterday and found it strange that it wasn't the same feeling you were getting with your 08 charger when MDS engaged. On your next cruise use the manual mode with the shifter placing it in
Top gear Not "D"rive... 5th for you I believe. Now MDS will not engage and see if you can duplicate the bump feeling. If you can't reproduce then it's MDS for sure. If it does happen it may be your torque converter lock/ unlocking. Which it should not do during steady throttle - equal load cruising. That would be a problem worth looking into.

 

That is how I tested mine when I felt that weird feeling and all was well, that MDS can really be felt sometimes dependent on road conditions
STEVE