Why on Earth do people want to disable MDS? (Hemi newb here)

[Matts175]

OK. So I've only had my Hemi for 6 days now. Loving the hell out of this MDS stuff! Why? Because I'm coming from a 2003 with a 4.7 that got an average of 14.6 MPG over almost it's whole life. With this new one, I'm getting a solid 15.0 (I reset it on day 1) and I now have 150 more hp (2003 4.7 is rated at 245 hp). And, I've been "punching it" a lot. I bet that'll go up to 16, once I calm down a bit. So, I'm thinking that this is all because of the MDS. Seems like a win/win. So, why are there Youtube videos/posts on here, etc. showing how to disable it? Why wouldn't you want good MPG? How does it make the truck any faster, seeing how it instantly turns on and off?

Not trying to start an argument here, just trying to gain an understanding.

 

[Mr.AK902]

1)Most folks don't like the "drone" it produces, it is bad with the stock exhaust and magnified with louder exhaust systems.

2)Some feel as if active cylinder technology like MDS leaves you're motor and internals subject to premature wear, Has been a topic among all brands using this technology since its inception.

Personally, MDS doesn't bother me. I could care less wether I have it or not. The only time i could see it being a pain is when towing, but it is deactivated automatically when you engage the tow haul button so that isn't a problem.

 

[chrisbh17]

MDS is fine on the highway. But when you are tooling around the city going from 0-30 to 20 to 30 to 10 to 0, etc, MDS makes the engine feel like its lugging as it engages and disengages. Its not nearly as evident at 60+ mph on the highway because your speed variations are much smaller.

I personally dont like putting such a strain on the engine...it might not make any difference to longevity, but it makes me feel better not lugging it in and out of MDS. Plus I like keeping it maxs at 6 or 7th gear when going around the city, and doing it that way automatically cancels MDS anyway.

@Mr.AK902 at least on my '17, Tow-Haul does NOT seem to disable MDS. I think others have reported that too. The only way for me to disable it is use the Gear -/+ buttons to pick a max gear of 1 thru 8.

 

[1500ram12]

Depending on your driving (city/highway), setup (lift/wheels /tires/exhaust) you may not see any gains and may come on for a second or two multiple times during a trip. If you have an exhaust when mds kicks in it becomes like a muffled fart (for lack of a better discription). For the typical person mds is fine. For most of us it's not needed or wanted.


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[jws123]

1 it saves no gas maybe like a dollar LOL
2 the lifters go bad faster and engine is noisier when it kicks in.
3 its annoying as ****.

its a failed design i took my mds 100% out of my truck put non mds lifters never goin back nor buying another mds vehicle.

 

[Burla]

What is MDS= A mechanical tool that shuts down 4
Cylinders and sends the same fuel to the active cylinders, so you have twice the fuel going to active Cylinders and 4 shut down. And then off and on off and on. It is horse **** on a fkin bagel. If they wanted to have a bullet proof system, they could have given the hemi a PI turbo with a 8 speed that didn't pre heat fluids. Likely would get better gas mileage then anything we have. But that would make sense, so you will never see it. The auto industry wants stuff that are gimmicks with short 1/2 lifes because they need to keep selling them.

 

[Ratket]

^ what burla said.

Also you can not go off of ur dash display for estimated MPG, you will need to hand calculate.

On a long flat low speed drive with a tail wind you will net some better mpg”s, but with real world driving, not really.

 

[MADDOG]

The fuel savings, which are miniscule or almost non-existent which is what I experienced, are not worth the noise, lack of throttle response and engine wear caused by MDS.

But that's just my opinion.

 

[S0CAL]

The fuel savings, which are miniscule or almost non-existent which is what I experienced, are not worth the noise, lack of throttle response and engine wear caused by MDS.

But that's just my opinion.

^ this

 

[BruceMorgan]

I'll have to try disabling it for a while and see if I notice anything different. Most of my driving is city streets and the ECO light is constantly going on and off, and yet I never hear or feel a difference. Throttle response seems fine to me, but it's a truck not my Corvette so maybe my expections are set too low. Bone stock exhaust sounds fine too.

 

[joshuaeb09]

The 2019 rental I'm in right now is way smoother on MDS engagement than my 16 ever was even after the latest updates. That and the horrible drone along with what @Burla has already covered is why it's disabled in my tune. I also get better mileage with it killed after going to bigger/heavier LT E1 tires when doing straight highway driving.

 

[jws123]

I'll have to try disabling it for a while and see if I notice anything different. Most of my driving is city streets and the ECO light is constantly going on and off, and yet I never hear or feel a difference. Throttle response seems fine to me, but it's a truck not my Corvette so maybe my expections are set too low. Bone stock exhaust sounds fine too.

Eco light has nothing to do with MDS mds is gone and mine still comes on. When mds kicks in you will know it truck bogs down like its in to high of a gear is best way to describe.

 

[Matts175]

OK. I get it now. Maybe I'll understand totally when next week on Thursday my buddy is installing a Magnaflow to replace that "hot water tank" that's under my truck right now. LOL

Thanks for the explanations.

 

[MADDOG]

With a bone stock exhaust you won't hear it. But a LOT of Hemi owners, cars and trucks included, don't leave their exhaust stock. In many cases they also remove their resonators. The combination of aftermarket exhaust and no resos tends to bring out the worst in exhaust system resonance on MDS motors.

 

[huntergreen]

My eco is very smooth on my 16. On longer hwy trips, it does give me 1.5 mpgs more than without. Around my rural area, no difference between when it's active or when turned off.

 

[Pull Ya]

I manually shift my truck into "7" and leave it there while driving around town and when driving under about 50 mph. Stops it from "lugging down".
Jay

 

[RLJ10X]

Some guys say it saves gas. Some guys say they do better with it turned off. Who knows? Gas is cheap right now, and there are better ways of saving money than to run a V8 engine on 4 cylinders.

Driving one of these things simply isn't a saving proposition, period. I don't mind spending a little money on my truck.

 

[BruceMorgan]

Eco light has nothing to do with MDS mds is gone and mine still comes on. When mds kicks in you will know it truck bogs down like its in to high of a gear is best way to describe.

You're right! I thought it did. The PDF version of the manual says zero about the ECO indicator, but the web says that it means the computer has determined you are driving "economically". Further, the web says if MDS is enabled, then ECO is definitely also on. So ECO means "maybe MDS, maybe not". No ECO means no MDS.

The manual also says zero about MDS. The general way most people disable it is using the Gear buttons on the steering wheel and set it to 8; the transmission will still use all the gears but won't engage MDS.

I'll have to try that then and see what I think. I've never used the Gear buttons before, and tow/haul only when towing.

BTW my C7 Corvette also has the Chevy version of MDS, enabled in Touring or Economy mode. It will drop the engine into V4 mode at idle or cruising. It's pretty much invisible, never gets in the way, and doesn't cause any sort of bog.

 

[TonyMM]

If you want a good mpg go for the mini diesel!

 

[Hemi395]

MDS in a car does actually save fuel (albeit by a small amount) but in a truck the savings are miniscule at best. It's more to show the EPA that "see were putting that awesome fuel saving system in the trucks too!"

I've had mine turned off for over a year now and I've maybe lost .5 mpg overall. But having the all 8 cylinders ready to go is really nice.