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  1. #1
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    Engine Stutter in MDS Mode

    I know this has been discussed before

    Irregular engine sound - hard to describe

    but my 92K mile '08 Magnum RT has just started to stutter below 1500 rpm in MDS, engaging Auto-Stick or accelerating to 1500 stops the stutter. Changed oil and cleaned the throttle body but little difference. Not showing any codes.

    I know this is a common ailment but what's actually causing the stutter? Is there a problem in one of the cylinders that remains running in the MDS mode? Or in the MDS system itself?



  2. #2
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    I was having what I described as a vibration, or at least sounded like it, though it wasn't anything I could feel through the wheel...but couldn't point to if it was motor mounts just transmitting more noise through when in MDS mode or a problem with MDS. Seemed more pronounced when traveling a lower speeds and felt like the MDS system was not disengaging as fast as when new.
    Or to put it another way, I was much more aware of the MDS system operation where when the car was new, I couldn't tell when it kicked on.

    With no real answer to the issue, along with the expense and its not an easy job to remove the MDS solenoids, I decided to simply turn the system off.
    I've found only on ave. 1-2 mpg difference and not worth the $$ savings in fuel to spend the time or money to mess with in my situation.

  3. #3
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    The upside has been a much more responsive engine at low speeds, so maybe the MDS system was getting lazy in mine.

  4. #4
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    Turn off the MDS with a tuner? My state has emissions testing and tuners are iffy.

  5. #5
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    Quote Originally Posted by Root66 View Post
    Turn off the MDS with a tuner? My state has emissions testing and tuners are iffy.
    It won't bother emissions testing at all.

    Sent from my XT1650 using Tapatalk

  6. #6
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    Brings a question I have wondered about..' with high mileage on engine, if MDS is engaged, can it be possible those 4 cyl that now do all the work, aren't as healthy [ring/valve ware] that they use to be, and you can now feel the struggle engine has in propelling this heavy car...?? Has anyone ever performed a compression test on all 8 cyl of MDS eng...with high mileage..? Would seem to me...ware should be different between the pairs of 4...But, I'm not a mechanic...

  7. #7
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    Quote Originally Posted by punisher69 View Post
    It won't bother emissions testing at all.
    From what I hear it will show up in the OBD port and trigger a failure. I'll ask on the forum.

  8. #8
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    I'm telling you, I just passed OBD2/emissions testing (with MDS off) without even putting the stock tune back in and it doesn't hurt anything.

    There are too many people with it disabled in tunes to be a problem.

    Sent from my XT1650 using Tapatalk
    Last edited by punisher69; 03-18-2019 at 02:03 PM.

  9. #9
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    Quote Originally Posted by Root66 View Post
    From what I hear it will show up in the OBD port and trigger a failure. I'll ask on the forum.
    I had my NYS inspection done at the end of January - I'd been running the 91 CAI tune all year with the MDS off and switched back to the stock tune the morning of inspection.
    While I passed safety, I failed emissions because the "OBD Readiness Status" was "Not Ready." The shop guy asked if I had disconnected the battery, as doing that will cause the same issues. I didn't tell him that I had a tuner and put the stock tune back on, but I guess that also causes the OBD to reset as well.
    The shop guy said to drive it for a couple of days and that should give the OBD enough data to be determine the readiness of the evap and O2 sensors and then be ready for inspection.
    I drove the car normally for 3 days and brought the car back and it passed in emissions. There is a thread in here somewhere about all of this, or search "OBD Readiness."

    So, tuners can be used and will not necessarily trigger emissions failures - just don't add, modify, or change a tune immediately before inspection. Do it a few days, to a week, prior.

    As for the engine running rough while MDS is engaged, my car has about 105,000 miles on it and I can easily tell when it's engaged during low RPM - it runs a bit rough. During highway cruising I can't tell and, for me, the couple of extra MPG doesn't hurt on long drives.
    My plan is to keep the MDS on during the winter because the AWD lowers the MPG and turn it off during the summer for those fun times!
    Brilliant Black 2010 300C, 5.7, AWD. Currently all stock except for lower intake silencer removal and home-made CAI, black plasti-dipped exterior trim and all interior lights replaced with LEDs, Intune i2. More mods when more $...

  10. #10
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    Quote Originally Posted by OlGeezer2018 View Post
    Brings a question I have wondered about..' with high mileage on engine, if MDS is engaged, can it be possible those 4 cyl that now do all the work, aren't as healthy [ring/valve ware] that they use to be, and you can now feel the struggle engine has in propelling this heavy car...?? Has anyone ever performed a compression test on all 8 cyl of MDS eng...with high mileage..? Would seem to me...ware should be different between the pairs of 4...But, I'm not a mechanic...

    Any Comments ?

  11. #11
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    HWDan is offline 2005 Magnum RT amd 2017 Charger SRT 392!
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    Quote Originally Posted by OlGeezer2018 View Post
    Brings a question I have wondered about..' with high mileage on engine, if MDS is engaged, can it be possible those 4 cyl that now do all the work, aren't as healthy [ring/valve ware] that they use to be, and you can now feel the struggle engine has in propelling this heavy car...?? Has anyone ever performed a compression test on all 8 cyl of MDS eng...with high mileage..? Would seem to me...ware should be different between the pairs of 4...But, I'm not a mechanic...
    Anyone who notices this, do you still have a stock exhaust? I would really consider mine having a very mild 'flutter' at low speeds which goes away as soon as I touch the gas or go up an incline enough, or even a bend in the road to switch off MDS.

    At one time, I was pondering the same thing. Until I got an SRT 392 in 2017. The 392 goes into MDS more often and sooner (at least so it seems) and it has the exact same MDS 'flutter' at low speeds as my old 5.7 but only only more pronounced due it's poor excuse of having stock mufflers that don't do much 'muffling'.

    Maybe the old exhaust is doing a little less muffling due to it's age, now making MDS at low speeds that much more noticeable that before ? I don't feel any difference at highway speeds but I know when MDS is on on the 5.7. With the 392, it's always obvious at any speed.
    Last edited by HWDan; 03-18-2019 at 10:56 PM.
    Hot Wheel Dan


    2005 Magnum RT and 2017 Charger SRT Maximum Steel!

  12. #12
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    Quote Originally Posted by OlGeezer2018 View Post
    Brings a question I have wondered about..' with high mileage on engine, if MDS is engaged, can it be possible those 4 cyl that now do all the work, aren't as healthy [ring/valve ware] that they use to be, and you can now feel the struggle engine has in propelling this heavy car...?? Has anyone ever performed a compression test on all 8 cyl of MDS eng...with high mileage..? Would seem to me...ware should be different between the pairs of 4...But, I'm not a mechanic...
    I'll give it a shot OlGeezer2018 . First, I wonder who is the "older" geezer, you or me? I have two somewhat modified 5.7's, an 05 Magnum with 87K on it and an 06 Jeep Grand Cherokee Overland with 113K on it. Both are modified exactly the same, except for cam advance, and run MDS friendly Sidewinder cams. I am not sure what you're calling high mileage (I am but I don't think either of mine are), but I've done compression checks on both within the last year. I pulled the heads on both to have all the valve seats replaced and, while they were off, I had them ported/polished and .030 in. milled off them to increase the compression ratio by about a half point. After all, a little better performance never hurt anyone. I did before and after compression checks, mostly to see how much difference there would be after they had new valve jobs and were milled.

    The Jeep's "pre-head removal" compression pressures ranged from 160-175 PSI with the MDS cylinders (1, 4, 6, 7) running 170, 170, 160, and 175 PSI respectively. The "after upgrade" compression pressures ranged from 175-200 PSI with the MDS cylinders running 185, 190, 175, and 200 PSI respectively.

    The Magnum, "pre-head removal" compression pressures ranged from 178-184 PSI with the MDS cylinders running 184, 182, 181, and 184 PSI respectively. The "after upgrade" compression pressures on it ranged from 200-215 PSI with the MDS cylinders running 208, 215, 200, and 215 PSI respectively.

    Right now I have my 06 300C SRT8 (obviously no MDS) with 165K on it torn down doing a cam/kit and valve job and, to give you an idea it's before compression pressures ranged from 154-175 PSI. It'll be interesting to see how much the pressures change when it's all back together. You can also see that the before compression pressures are not drastically different from the before pressures on engines with a lot fewer miles on them.

    By the way, I am about to catch 76 and been messing with cars since I was about 16.
    06 300CSRT8, stock, 06 Jeep GCO and 05 Magnum RT both modded almost the same, MDS "ON" Lt, Fumoto Drain Valves, BT Catch Cans, SRT8 CAIs, AFE Filters, Sonnax Trans Line Press Booster, SC, DS and HP Tuners, Transgo Shift Kit, ARH Long Tube Hdrs w/3 in Magnaflow/Xlerator AP Exh Sys, Bilsteins, SRT Springs/Sways, Cust Eng Cvrs, SRT8 frt/rear bumpers, FRI Sidewinder Cams advanced (Jeep 6*/Maggie 10*), 6.1 valvetrain, SLP 25% UD Pulley, BBK and Arrington 90mm T-Bodies, SOS Ign Coils,TEA ported/milled heads w/new valve seats, SRT Reps.
    Thanks OlGeezer2018 thanked for this post

  13. #13
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    Yup....You are the "Older" Ol Geezer...By a little...I turn 74 in few weeks...Your info is perfect answer...My first Charger, first Hemi...[but not first muscle ]...and MDS is something I never thought I'd be owning...Back in the days...engine ware always showed up [Comp loss] between cylinders , more so than with today's engines...Nice to see that MDS does Not become a concern...Thnx

  14. #14
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    Quote Originally Posted by HWDan View Post
    Anyone who notices this, do you still have a stock exhaust? I would really consider mine having a very mild 'flutter' at low speeds which goes away as soon as I touch the gas or go up an incline enough, or even a bend in the road to switch off MDS.

    At one time, I was pondering the same thing. Until I got an SRT 392 in 2017. The 392 goes into MDS more often and sooner (at least so it seems) and it has the exact same MDS 'flutter' at low speeds as my old 5.7 but only only more pronounced due it's poor excuse of having stock mufflers that don't do much 'muffling'.

    Maybe the old exhaust is doing a little less muffling due to it's age, now making MDS at low speeds that much more noticeable that before ? I don't feel any difference at highway speeds but I know when MDS is on on the 5.7. With the 392, it's always obvious at any speed.
    Dan, I see you joined the forum a month after I did back in 2004. I haven't been around much for the last several years....life sometimes gets in the way. Anyway, back when yours and my 05's came out, remember the Hemi's with MDS were "big mysteries" and there were no aftermarket parts available. Many members on here loved to experiment and tinker to try and figure things out, The MDS was one of them. I don't know if you've added the MDS "ON" Light that I came up with back in early 05 (Installation of a MDS ON Indicator Light) when everyone still pretty much had stock exhausts and tuners were not yet available. (I've since removed the switch and moved the position of the light.) If you haven't installed it and still have a "quieter" exhaust on your 05, you may want to consider adding it. It helps you learn how/when it turns on/off, how you can "coax" it to come on, and can help gain better fuel economy IF that is of interest to you. My 05 Maggie (with my mods....see signature) with more than 100 hp. more than stock normally gets 27-29 mpg (once in a while 30) on the highway and around 15-17 mpg in town depending on the amount of stop and go driving.

    Neither of my 5.7's have the flutter you folks are talking about, but I have tuners on both......original Diablosport Predator on the Magnum and original Superchips Flashpack on the Jeep, both augmented and modified with the HP Tuner. I can't imagine what could cause this?? Does it appear to be like "flat spots" or jerking?? The tuners take away some of the smoothness and make you "feel" the MDS kick in, mostly at lower speeds, but they also allow for much more MDS "on" time. I think the stock smooth transitions also adversely affect the amount of on time. I've run mine stock and it's absolutely terrible, IMO. On the highway (level), the Magnum MDS active time is more than 95%. On it, I also have a Getrag 3.06 LSD, modified the shift schedules, torque management and torque converter lock up settings which I believe all make slight improvements too.

    Your 392 more than likely gets more MDS "on" time because it has more horsepower and torque. One of the main parameters that turns the MDS on is engine load. On both of mine, at elevations of 2500-4000 ft., anything below ~31% engine load will allow it to come on. At sea level this %age raises to ~35%, because at sea level they make more power/torque. Most completely stock early 5.7's can't climb even the slightest incline without the MDS shutting off.....not true with a tuner and more power.
    Last edited by magnuman; 03-19-2019 at 01:01 PM.

  15. #15
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    To add a little more to this thread dealing with the engine stutter/flutter in MDS mode, a member (don't know if he's still on), magnumrt, back in April of 05 gave a little insight into the complexities of the MDS and the many things that impact its operation. As I said, we all liked to tinker and experiment with the unknown back then. Here's the quote from one of his posts in a thread I started when I was going to try and override the PCM and turn the MDS on/off as I desired. The thread is titled, "MDS ON/OFF Switch" and here's his post:

    "The MDS system is much more complicated than most people realize. The design of the system took MANY more years than you may think, I actualy started working on this system back in 01 in some DC concept vehicles. Trust me, there were many issues to try and get it right. One of the requirements for this system was the electronic throttle controll. When you deactivate 4 of the 8 cyls, you get about a 50% reduction in air requirements meaning that when you hold your foot on the gas at 25%, in V8 mode, the throttle blades are at about 25% open, but when you go into 4cyl mode, we need to immidiatly adjust the throttle to about 15% throttle without YOU fealing it. This is an extreamly complex algorithm and is QUITE heavy in closed loop feedback with the MAP sensor, Crank/Cam position sensors, Input/output shaft speed sensors, etc. Also when you move from 8-4cyl there is obviously less vacuum being drawn by the motor. Lower vacuum to the MAP sensor is translated normaly as a higher load on the motor, but you need the PCM to realize that this is not the case at this particular moment. Now, as far as your question of why the motor doesnt stay in MDS longer to give you better fuel mileage? That is another compicated story that has been tuned quite extensively to give the best overall gas mileage without issues. When the lifters cut out and trap exhaust gasses in the cyl, that gas acts as a spring to keep the motor from wasting energy while the inactive pistons are going up and down. This gas begins to loose it's energy because the cyls will tend to leak a bit (through the rings and through the valves). The motor needs to re-initialize the cyl to allow the spent gases to escape. Now, the question is, why do you not re-initialize right away to save more gas? Simple, you gotta keep the engine's temperature equal so that you dont have 4 cyls working at a different opperating temperature than the others. The 4 cyls that are not firing will get cold as well as the valves, intake runners and specificaly the exaust pipes. Cold exhaust pipes dont flow as well as hot pipes and therefore you get an imbalance in those 4 cyls when running in V8 mode. The timing has been optomized for all these conditions to occur as transparently as possible. Extending the MDS time or frequency would end up creating more problems than are apparent to most.

    So yeah, in conclusion.... It aint easy to do, there wont be any way for quite some time for you to increase the amount of time the MDS turns on for the simple fact that the design aint simple ;-) Not to mention the strategy has been developed to be as optimal as it could be. Trust me, the goal was fuel economy and transparency, TONS of time and effort went into making it as good as it can be."
    Last edited by magnuman; 03-19-2019 at 01:57 PM.

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