Tuning MDS, Actually tuning it for highway operation only...

Hi, Yes an MDS thread, but NOT a how do I turn it off thread...

I am actually interested in seeing if the MDS feature is actually tunable.

In the Rom under Fuel > Lean Fuel Saving > MDS you have 5 tables:
MDS Active/inactive Switch
VSS Min MPH
VSS Max MPH
ECO VSS Min
ECO VSS Max

Stock values are:
Enabled
8 mph
128 mph
9 mph
128 mph

I tested and set the VSS min for MDS to 55 and the ECO VSS min to 56, and it never activated.... Almost as though the subroutines with these specific VSS tables are either not defined, or the tables themselves might be mislabeled and other subroutines don't see this as actual Vehicle Speed... Also, maybe there are other switches or tables that need to be adjusted to understand the new minimum speed settings...

So I am curious if anyone has tried to tune it, so that it is used only on the freeway above 65 MPH...

Thanks in advance

GM sure gives a lot more. Bet this info is available for MOPAR.

https://i.imgur.com/RgQ7EQZm.jpghttps://i.imgur.com/CSfuBq8m.jpg

I seen some other people report on this, yeah if you make it anything over 45mph I think, it just won?t come on. The subroutine or something hard coded won?t accept anything past a certain value.

I've been messing with MDS on my 2010 Jeep Commander with the 5.7. One thing I noticed is that mine can't really stay in MDS above about 55mph. Looking at with the VCM Scanner, this is about the point where the Manifold Air Pressure (MAP) reaches 95kPA and above, and I believe this is why the MDS shuts off.

I think this it has to shutoff MDS once the MAP is near atmospheric, this is essentially wide open throttle...the engine is getting all the air that it can, and developing all the power it can....once it reaches that point, it has to put the other 4 cylinders in or I could foresee the engine would start lugging and break something.

I do have to say its pretty crappy for this Jeep to be running on 4 cylinders, and they are getting full atmospheric pressure (an engine size the equivalent of 5.7liters/2=2.85liters) and it can barely keep this Jeep cruising steady-speed on a flat interstate at 60mph...lol.

I also noticed mine is picking up knock, and pulling as much as 4deg LTKR off an on when in the 4cyl mode. I put in some 93 octane and KR didn't go away, at this point, I believe its false KR, or noise from the non-driven pistons sloshing up and down, because there is no pinging noise, or stumbling. Out of frustration, I raised the knock voltage sensitivity on all 8 cylinders to max (5V) at both 1000 and 1800RPM (between these RPMs is where MDS operates in 5th gear below probably 80mph)...thinking that mine might have trouble developing proper power in 4cyl mode with the timing being retarded off and on by this false KR. So logging again it runs smooth as glass, just like before, absolutely no KR is accumulating, but unfortunately it changed nothing, and the Jeep still can't run in MDS near or above 60mph.

Out of curiosity, since MDS is only useful if it improves fuel economy, I created a custom PID to total all 8 cylinder injector PW values. The idea being, this sum of total injector PW is an indicator of fuel consumption. We should find the sum of 4 cylinders is less than 8 at the same speed/load if the fuel economy is going to be any better. I find (if anything) the sum of 4 cylinders is either equal to or greater than all 8 cylinders ... which is to say, the 4cyl fuel economy is either equal to, or worse than 8cyl mode. At 30-40mph I find its 30% WORSE in 4cyl mode than 8cyl mode, lol.

Have you logged your MAP pressure when you are in 4cyl mode? Depending on how close it is to 100kPA, you can get a guess as to how close you are to maxing out the capability of 4 cylinders at that speed/load.

P.S. I'm not sure what you are using to verify when you are and are not in MDS. There is no "MDS active" PID or equivalent that I could find in mine. I show it by logging and charting Cyl 1 injector pulsewidth. Since when MDS goes active you can observe cyl's 1, 4, 6 and 7 drop to 0msec, while you observing cyl's 2, 3, 5 and 8 jump up to double or more at same operating speed/conditions.

Quote:

---

Originally Posted by coanan

GM sure gives a lot more. Bet this info is available for MOPAR.

https://i.imgur.com/RgQ7EQZm.jpghttps://i.imgur.com/CSfuBq8m.jpg

---

What do the values look like in your "Disable Vacuum" table? Just curious...

Quote:

---

Originally Posted by ngc1068

What do the values look like in your "Disable Vacuum" table? Just curious...

---

We have Zero (0) Tables like yours. We only get the tables I listed under the initial post...

Quote:

---

Originally Posted by raceghost

We have Zero (0) Tables like yours. We only get the tables I listed under the initial post...

---

Yes, in the right collumn near the middle you have a table "Disable Vac", i'm curious what are the contents in your tune in that table. (sorry, ignore this was talking about coanan's post)

Quote:

---

Originally Posted by ngc1068

What do the values look like in your "Disable Vacuum" table? Just curious...

---

https://i.imgur.com/6bnogQKm.jpg

Quote:

---

Originally Posted by raceghost

We have Zero (0) Tables like yours. We only get the tables I listed under the initial post...

---

HPT has a better grasp on tuning GM.

There has to be the same tables in MOPAR, just not shown in tune software.

Attachment 111823

This is what I have...

No other vacuum tables to speak of.

Updated with copy of stock rom, while this is a Police Interceptor Rom, can verify it looks like the R/T roms of same year, this is 2009.

Bump for anyone still playing with this.

There is no doubt tables exist that govern MDS that we cannot see in HPT. I guess we need to put in a formal ticket and see if anything is done.

I have worked with HPT support on this years ago and they found it locked for the most part but for the minimum activation being limited to 20mph.

MOPAR allows the dealerships this small window mostly for trucks that go to larger diameter tires to the point they lug in the lower speeds w/MDS on so they allowed the bump to 20mph.
Like HPT the dealerships tool is limited the same.

What would really help is to involve the transmission somehow in the MDS operation. Since the engine cant produce enough torque/power in 5th at cruise above 50-60mph, it would help ALLOT if the transmissiom downshifted into 4th, for example. You notice 4cyl engines are already geared to run a higher RPM at a given cruise speed than larger displacement 6 or 8 cyl engines. Of course as the MDS arguably already causes hesitation, I’m sure an odd down/upshift thrown in there would really have made owners pissed off…but i think this would be the only way to get the 4cyl’s to produce enough power/torque so that MDS has a chance to stay active at higher speeds. Unfortunately if you use the autostick to downshift, it turns off MDS…and there seems to be no way to adjust the MDS to stay active and available after autostick is shifted to “manual”…the two are mutually exclusive…*sigh*

Yeh, I was into it after installing a Corsa Sport CatBack it sounded like a lawnmower when it came on @9mph when just lugging around town. The bump to 20mph minimum relieved lots of that.

No matter now as I have an EForce Blower on her now with MDS tuned out. I have a post here asking if anyone has left MDS enabled with a blower install. I know there is no way it will be in boost on 4cyl but I cannot find testimony on anyone trying it.

2009 5.7 Jeep GC. My MDS never stayed on past 1100rpm
I never did figure it out and shut it off for the time being.
I've been meaning to look at it again.