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Discussion Starter #1
Had semi performance mufflers on my 2014 Charger SRT and no resonators. Recently I had Powersticks installed and these are very close to straight through pipes. I'm now noticing that the MDS (switching to 4 cylinders) almost never comes on. The only time I'm noticing it turning on is when I'm decelerating. It used to come on all of the time when I was maintaining my speed (above something like 30mph). That does not happen any longer. Does anyone know if something like back pressure might trigger the MDS to kick on? It is certainly related to the change in the exhaust as it was working fine the day before and the day after it changed.
 

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I don't know for certain...But I always thought that the back pressure is 'needed' for 4 cyl running...something to do with proper combustion in the head, EGR functions etc..Maybe a engineer will chime in..
 

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Back pressure has zero effect on MDS. Speed, Throttle pedal position, engine load, oil temp, oil pressure are the main factors in it's function.

Do you tell MDS is on by sound or are you going by the light (ECO). Cause the ECO light where it shares a few same operating parameters is not a MDS indicator.
 
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Discussion Starter #4
Do you tell MDS is on by sound or are you going by the light (ECO). Cause the ECO light where it shares a few same operating parameters is not a MDS indicator.
I have a 2014 so it's not the ECO mode that you mentioned (i.e. it is only MDS). I go by the MDS light as this lights when the engine goes into 4 cylinders. As mentioned, it use to come on when I was just touching the pedal light enough to maintain a speed above something like 35mph. Now, when I do this to maintain 45mph or 70mph, it does not come on at all. It only comes on when I release the pedal completely and I am coasting. This happened the day I changed the mufflers and nothing else.
 

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Since when is there an MDS light?
 

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That doesn't mean MDS. That just means you're below some threshold of throttle.
 

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MDS is the car going into 4 cylinders. Aka. Eco...
 

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Discussion Starter #9
Since when is there an MDS light?
I stand corrected. I meant ECO light... but the difference is that the 2014s don't have ECO mode like the newer models... ECO on the older models is switching to 4 cylinders only.
 

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Eco does not mean it's in 4cyl mode. There are times where Eco is on but still on 8. Not the other way around though.
 

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Discussion Starter #12
It is difficult to know who is replying to who without quotes. I think I lead to some confusing but to get past ECO and MDS mode, here is the information from the manual on the ECO light and MDS mode:

There is an ECO icon between the Compass and Outside Temperature info at the top of the EVIC display. This icon will appear whenever the Multi-Displacement System (MDS) (if equipped) allows the engine to operate on four cylinders, or if you are driving in a fuel efficient manner.

Dodge changed what ECO mode is in later models and this leads to some confusion. In the 2014 model the ECO light only means it is MDS mode.
 

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I still believe Tcope is "correctly" noticing that eng will no longer go into 4 cyl mode when he is driving in the same exact conditions...And I still think it is exhaust related...lack of back pressure....My wifes older GM car had it's muffler removed ...straight pipe...and it refused to allow EGR function..[electronic control module pulses [sq wave] based on back pressure....Her computer sets the "service eng soon " light...There have been articles on late model advanced combustion techniques ...jibberish to me, about flame spread and such...and how backpressure , now, is a Needed thing....seems obvious, Dodge engineers [along with EPA requirements] took it into consideration on software that allows 4 cyl operation...IMO
 

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Im curious how the ECO light and MDS mode are interrelated as appears from some comments.

When I select ECO drive Mode my ECO icon is illuminated whether or not the car switches in or out of MDS. All ECO mode does on my car is start out in second gear, has less response to throttle input, and shifts gears slower. I can disengage ECO my going into another drive mode, or moving the selector from auto to auto-stick.

MDS will work whether of not ECO Mode is selected but if I am not in ECO mode, MDS will not activate nearly as often as when I am in ECO Mode where the car is sluggish.

If I scroll down to Fuel Economy on the center console it will read 4 cyl when MDS activates

As far as what algorithm is used to activate MDS; I doubt anyone knows except the software engineers that program it.


EDIT: I now read post #12 about 2014 model year. I was busy smashing the keyborad before it was posted.
 

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My MDS operated perfectly without mufflers. Backpressure has zero to do with MDS. There is no connection. Also, ECO light still does not mean MDS is working. Read it.

This icon will appear whenever the Multi-Displacement System (MDS) (if equipped) allows the engine to operate on four cylinders, or if you are driving in a fuel efficient manner.

You can have one or the other, or both. Both share same operating parameters but can operate separately. I have MDS removed on my Pursuit and I still get a ECO light. I could also before when I had MDS be in 4 cylinder mode and cause the ECO light to go off with heavier throttle position.

Chances are with louder exhaust been throttle it a bit more or in sport mode and it stays off. Although with different exhaust you should really tell when it is in MDS due to sound change for sure.
 

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I still believe Tcope is "correctly" noticing that eng will no longer go into 4 cyl mode when he is driving in the same exact conditions...And I still think it is exhaust related...lack of back pressure....My wifes older GM car had it's muffler removed ...straight pipe...and it refused to allow EGR function..[electronic control module pulses [sq wave] based on back pressure....Her computer sets the "service eng soon " light...There have been articles on late model advanced combustion techniques ...jibberish to me, about flame spread and such...and how backpressure , now, is a Needed thing....and Dodge engineers [along with EPA requirements] took it into consideration on
software that allows 4 cyl operation...
There were only a few models of our cars that had the back pressure sensor. If his had one and that was the issue, the CEL would be on.

My '13 5.7 had 3" straight pipes from the cats back and my MDS still functioned normally with no CEL.

Sent from my moto z4 using Tapatalk
 

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Backpressure is one of those buzzwords that people toss around. An engine is an airpump, resistance to airflow is not a good thing. That's why people put on equal length headers and x pipes, for the scavenging/vacuum effect.
 

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Tscope, it is highly possible that IF you have a pressure sensor on your exhaust, that the sawzall on the exhaust vibrated loose. Again, you SHOULD have a check engine light if that's the case, but it wouldn't hurt to check and see.

If you have one, it'll be attached to the driver's side exhaust and you'll see a steel tube going down that side of the engine.

Sent from my moto z4 using Tapatalk
 

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Discussion Starter #19
You can have one or the other, or both. Both share same operating parameters but can operate separately. I have MDS removed on my Pursuit and I still get a ECO light. I could also before when I had MDS be in 4 cylinder mode and cause the ECO light to go off with heavier throttle position.
So we'd agree that the MDS light will come on when in 4 cylinder mode (and you state it also comes on when getting better mph). Regardless, it use to go into MDS mode when using the accelerator to maintain speed. Now it will only come on when removing all pressure from the accelerator. The only thing I've changed is the mufflers. It was working that way an hour before install and the next day it was not working that way.
 

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Punisher69 relates to a backpressure sensor that may report to the computer...I believe it is Not necessary to have the sensor...I feel the software notices a loss of Torque...and realizes too much strain on the eng dropping to 4 cyl..[very heavy car]....therefore prevents MDS...I found this statement in a PDF file of engineers discussing backpressure:
"it depends on what you are trying to do. It will change the torque-horsepower curve. In simplistic terms, reducing the backpressure will decrease torque and increase horsepower. So what is it that you are looking for? Reducing the pressure to zero, by removing the exhaust system completely is going to cause problems, as is restricting it so much that the engine can’t rev. Compromises are made to find the proper operating condition "
 
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