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Discussion Starter #1
Ok, generally I haven't had any serious issues with my 05 300C since it came off warranty 30k miles ago. Recently though, some strange things have been happening. I know it's not running right because you get used to what is normal for a car you've owned for a long time - you know what I mean.

The most obvious problem was last night on the highway - 15 degrees out and I could swear that the MDS was coming on when it shouldn't. When going up hills and accelerating, it normally goes off immediately, but I could tell it was staying on because of the obvious change of exhaust sound and the lack of power. My son and I listened to the engine loping up and down when I was trying to accelerate. It was as if the engine was fuel-starved - definitely lagging.

Anyway, when we got off the highway I found a dry spot and pegged it from a slow roll. The car launched normally, so I know fuel pressure and filter must be good. Then, when going slow through our neighborhood, the MDS came on and would not go off. When I tried to accelerate, the car shuddered a little (like lagging a manual in overdrive). I immediately thought there was a problem with the torque converter, but because the MDS was obviously on (definite change in exhaust sound), I am kindof convinced that this is the problem.

Now with all of that being said, I did the smart thing and came here for a visit. I see some notes about an MDS reset after a battery change, which until now, I never heard of. I did have the battery replaced about 2 weeks ago. Bear in mind that I have a scantool and there are no trouble codes at all.

I will try the MDS reset later today, but I am wondering if this really is the cause or if there is something else going on, like a bad sensor or something. I put on the "easter egg" diagnostics when on the highway and checked the TPS % reading. It was a-ok, reading 0 with my foot off the pedal, and ramping up properly, so I can eliminate that.

Any thoughts or comments? Other things I should check?

Thanks in advance!
 

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Do you have a Predator, if so try turning the MDS off and try the car again. This would confirm an MDS problem. Have you changed the oil, too heavy a grade will affect the correct functioning of the MDS system, 5w / 20 oil is recommended.
 

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Discussion Starter #3
Unfortunately no predator. Oil is Mobil 1 5w/20, but I did get stuck about 3 weeks ago and I had to put a quart of slightly heavier Mobil 1. I know one has the green cap and one has the blue cap. That is interesting. I wonder what the relationship is to the oil...
 

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Discussion Starter #5
Ok, just came back from the MDS reset experiment. I think you were on target as I see it.
Before I left, I warmed it up and put my scantool on. Found code 1521 (only code found), but no MIL, so without the tool, I would never know. Reset 1521 and it came back before I left the driveway.

Went out and did the MDS reset - twice (that Hemi is an awesome motor). Noticed a little change the second time. As part of the procedure, I cleared the codes and the 1521 did not return.

Here is what I think this is about... cold weather and oil. I think that based on what I've been reading, 1521 indicates that the wrong oil has been used. I had added a quart of the thicker Mobil 1 instead of 5/20. The consensus is that MDS will not work properly because the lifters can't bleed down fast enough with the thicker oil.

So, if the viscosity of my oil is borderline with this added quart, add in the cold weather (19 degrees right now), then it could well be that the MDS can't bleed down the lifters fast enough when shutting off the 4 cylinders. This could well be where the disengagement problem I noticed is coming from. Not knowing exactly how MDS works, I can only assume from what I've read that the lifters have to bleed down to take the action out of the valve train.

I read a thread in the Dodge forum about a guy who blew his motor because of this. It does surprise me to a great degree that the ECU doesn't set the MIL to alert the driver and disable MDS. This would protect the engine in a case like this and avoid the worst.

So, the lesson is that the oil really is critical! It will sit in the driveway until tomorrow and then right over to get a full change tomorrow.
 

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You can prevent MDS from functioning if you use autostick, ie take it out of D (drive).
 

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Did you think that the MDS reset procedure made any difference?
It also states in the handbook that the MDS may take sometime to return to normal functioning after a battery disconnect.
You could also try disconnectig the battery again for 10 minutes and after that pull fuse 11 for 30 seconds, then road test again.
If you think engine oil is suspect, change oil and filter asap.
 

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Ok, just came back from the MDS reset experiment. I think you were on target as I see it.
Before I left, I warmed it up and put my scantool on. Found code 1521 (only code found), but no MIL, so without the tool, I would never know. Reset 1521 and it came back before I left the driveway.

Went out and did the MDS reset - twice (that Hemi is an awesome motor). Noticed a little change the second time. As part of the procedure, I cleared the codes and the 1521 did not return.

Here is what I think this is about... cold weather and oil. I think that based on what I've been reading, 1521 indicates that the wrong oil has been used. I had added a quart of the thicker Mobil 1 instead of 5/20. The consensus is that MDS will not work properly because the lifters can't bleed down fast enough with the thicker oil.

So, if the viscosity of my oil is borderline with this added quart, add in the cold weather (19 degrees right now), then it could well be that the MDS can't bleed down the lifters fast enough when shutting off the 4 cylinders. This could well be where the disengagement problem I noticed is coming from. Not knowing exactly how MDS works, I can only assume from what I've read that the lifters have to bleed down to take the action out of the valve train.

I read a thread in the Dodge forum about a guy who blew his motor because of this. It does surprise me to a great degree that the ECU doesn't set the MIL to alert the driver and disable MDS. This would protect the engine in a case like this and avoid the worst.

So, the lesson is that the oil really is critical! It will sit in the driveway until tomorrow and then right over to get a full change tomorrow.
Thicker oil might prevent MDS from activating but I don't think it could cause MDS not to de-activate; I guess it would depend on how much thicker as well, but I know that 5w30 for example won't damage anything - - the non MDS hemi's (05 and older Ram 1500's, all Ram 2500 / 3500's, etc. call for 5w30). I'm kinda curious though that you can tell when MDS is on by the exhaust sound; on my 300c I've never been able to detect when MDS is on or off.
 

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Discussion Starter #9
I'll be going for the oil change shortly and I'll update once I've driven it. James, I can definitely hear the difference in the engine's exhaust as it is only firing 4 cylinders as opposed to 8. Interestingly enough, the sound reminds me of the old multiport v6s that they put in the old camaros. There is also a slight rumble in the exhaust system when it is on. This is the way it has always been, and I've got 100k now. This is the first out-of-warranty issue I've had, excepting only to the off-the-highway-fuel-fill-left-turn-canister-stall issue, which only happened once.
 

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Discussion Starter #10
Ok. Oil changed and it seems to be back to normal. Interesting... very sensitive to oil viscosity and cold weather.
 

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Possible MDS solution, 5.7

I read a post, here I think, where the author's MDS stopped working. It turned out the wiring harness had rubbed on something and wore through. Result? Short circuit and engine light (and he had a pix to prove it).

I rather like my MDS, but it is cutting in and out. Knowing the above, I grabbed the harness which goes under the manifold in back and has a connector behind the driver's side head (it's down low and close-in so it's not readily visible), and waggled both the harness and connector then drove it. Whaddya know, MDS came back, though but for a short time until I hit a bump.

I'm going to cage some connection cleaner from my Snap-On buddy and if that doesn't do it, I just may leave it alone. Assuming an MDS disconnected for a long time wouldn't cause FUBAR.

Ah, but I see eBay has a harness off a 2008 for $45. Hey, could be my savior. T/Sgt Ellis, USAF, told me to always check the easy stuff first, so tomorrow I'm going to wiggle the wire and clean the connector. If that doesn't do it, I'll pull the manifold and check out the wiring. If the wire harness is pinched, worn through or corroded, all I'll be out is $45 and gaskets. Of course if the harness is worn, but not too badly, I could just re-tape it and go on my way. I'll seek the council of my Snap-On buddy.

Last thing I want to do is go digging around in the engine (I've learned my lesson).

I'll keep you posted.
 
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