[tlkemp]

I recently bought a new 2007 GC Limited 4x4 HEMI. Had 17 miles on it when I bought it, and now has 2500. I have searched the forum but have not seen any posts that describe what I "think" I am sensing. I am pretty sensitive to vehicle ride and performance.

It seems to me that when cruising at highway speeds, I can sense a bit of surge in the engine. Have taken it in, even took the service manager on a test drive with an engine monitor plugged in. He can't feel anything and the computer does not show anything. He says it is just the suspension and the road, and I have honestly wondered if it was a bit of "buck" due to the short/tight suspension and the roadway. I have always had heavy sedans before.

However, on a recent trip on flat freeway, I watched the odo and could sometimes see it vary about 150 rpm while at 65 mph. On flat ground on cruise, I would think rpm would be consistent, no? Wondering if maybe it is oscillating in and out of 4 cylinder mode or something, or if the transmission is just not right. However, if their diagnostics computer is not programmed to sense what is wrong, seems I am out of luck with the service department.

[Texas WJ]

I believe what your sensing is the transition from four to eight cylinders. I've noticed it too on mine, but I'm also hyper-sensitive when it comes to my vehicles. I don't believe that it's a transmission issue, just the MDS doing it's thing. It is slightly annoying though.

[PropDr]

RPM changes at steady speed, is caused by the locking and unlocking of the torque converter.

[tlkemp]

Originally Posted by PropDr

RPM changes at steady speed, is caused by the locking and unlocking of the torque converter.

If this is true, am I destined to hear "it is performing as designed", or is there a fix if they can actually see it happen?

So far I have not been able to get a service manager out on a stretch of road where this can be witnessed.

[PropDr]

Sorry, I was not implying that it was normal.
I had a similar problem on my 98 5.9, and it was corrected by replacing the throttle positioning sensor.
Your Jeep has a fly by wire throttle actuation, so I don’t know if it has a similar cause.
Maybe the mighty Merlin will chime in.

[tlkemp]

Originally Posted by PropDr

Sorry, I was not implying that it was normal.

I hope not. I have just seen many posts of folks that had what they considered an issue and Chrysler/Jeep said it was normal or by design.

I'm getting it ready to tow behind my motorhome right now, so think I will wait and take it to a dealer in a less populated area, hoping there will be open roads more suited to them experiencing the issue.

[PropDr]

On a 2000 mile trip I did not experience this problem once.
Good luck finding a competent service center and let us know the outcome.

[merlinTec]

Hi
Not had any complaints of this myself but there are two TSB’s for the 5.7. one is 18—27-07 for an EGR fault code and the other 18-004-08 for catalyst efficiency fault code.
Both an EGR fault and an 02 sensor fault could course you fault but is not going out of running parameters so it’s not bringing up a fault code but you are sensitive enough to feel it.
When you went up the road with the service manager and he had start scan plugged was he looking at the MDS system as star scan will say when the MDS is in 4 cylinder mode so you know if it is MDS related.
First thing I would do is get them to update the PCM with the latest software.
Regards,
Merlin

[bob2375]

I have the same problem but is more pronounced and does it at almost all speeds when the pedal is steady, it is very evident on smooth surfaces and even got the Jeep mechanic to agree that there is a problem but they have not been able to fix it, it is like the engine is bucking or some gremlin is running the engine lean off and on, the engine runs like a champ when cold but the instant it warms up the gremlin does its thing. Any clues would be great.

[wrenchbendr]

man i thought i was being to sensitive to my jeep. this is exactly what my 05hemi is doing. if anything is found please post it here.

[icecreamman]

Same issue here. I bought it and drove it home 300 miles during which I noticed an almost imperceptable "surge" at 41000 mi. I drive for work and it steadily got worst now at 42500 (two weeks later) the transmission is DEFINITELY not behaving normally. On the way home I experienced the following symptoms:

-Erratic shifting when cold (20 deg ambient temp), sometimes too high sometimes too low
-Hard upshifts 50% of time
-A new one today: Hesitation (1-2 seconds) engaging from a slow speed coast with a hard catch and sling shot with <25% throttle
-strange non-stop engine vibration in second from 1500-1800rpms for as long as I maintain speed, then disappears as soon as I give it a little gas
-driveline shock (snap) with any change from no throttle to throttle application
-RPMs go DOWN as throttle is applied at highway speeds until about 50% when it BANGS down two gears 100% of the time
-Random inexplicable stutters on smooth highway

So I think I've read in this and other messages that this is a common problem with an electronic torque converter sensor. Anyone care to elaborate as this is ruining my Jeep experience.

[acsimon]

"Texas WJ" is correct. You are experiencing the MDS system. Sometimes on the highway with the cruise on you hit a stretch of road (slightly hilly,etc.) and the MDS is constantly slipping from 8 to 4 back to 8, etc. You can diffiently feel the surge. It's annoying, sorry, the price you pay for saving a little money at the pump. If it's impossible to bear, increase your speed to around 80, and the system won't come on.

[jeepfan30]

Or shift from "D" to "5" when you drive. MDS is not active unless you are in "D".

[RFisher]

I found that by pressing the gas pedal just slightly will keep it from shifting from 4-8-4-8. when I let it coast with no pedal pressure, it shifts erractically that way. seems that she likes to have some rpms while in 4 cylinder mode to keep it from shifting back and forth. I am not using synthetic oil, not sure if that maters. Just what the dealership adds, it is non synthetic.

[tlkemp]

Here I am almost 2 years later and this is still annoying the hell out of me. Had it in 4 times to different dealers. First three said they did not really notice anything, but then they did not drive it in conditions where it is most noticeable. Just wrote an online letter to Chrysler asking for help resolving it. If they are not able, lemon law arbitration is next.

Lately I have had it on I-75 (Alligator Alley) across Florida a few times. You can't find a much more flat, straight section of road that goes on for 100+ miles. Ridiculous a high tech vehicle can't find a constant speed/RPM setting in those conditions.