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Discussion Starter · #1 ·
Hi,
I am new to your forum, and since the Magnum and 300 share many of the same components, I thought I tell you all about I mod. I've done to my RT, and figure some of you may be interested. If the 300C is the same under the hood, and similar in the lower dash area, this mod. could easily be done. For what it's worth:

I decided I wanted to know when, how often, and how long the MDS system works on my RT, so I hooked up an MDS indicator light. Easy to do. I used an illuminated rocker switch for the light. This way, when it is on I can monitor MDS activity and turn it off when I don't want to monitor. The most difficult part of the installation was routing the wires into the car and finding a suitable mounting location. I ended up putting it under the ignition key. It is fairly inconspicous, easy for the driver to see and does not glare at night. What I have found after several test drives is that MDS doesn't even work until the engine is at about 130 degrees. It is extremely sensitive to throttle application. The slightest touch and it goes off. The latest it shut off when coasting down was 20 mph. Accelerate and just take your foot off the throttle didn't always make it come on??? On the highway it is very predictable and works almost continuously on level ground at cruise above 40-50 mph. I don't know all the parameters required to make it work, but by testing and trial and error I know the following have some bearing on when the MDS is active and when it is not. They are, engine oil temperature, engine oil pressure (haven't seen it work with less than 45 PSI oil pressure), gear selector position (must be in "D"), coolant temperature (haven't seen it on when temp. is below 130 degrees), vehicle speed, Manifold Air Pressure (MAP)/throttle position, and perhaps outside ambient temperature. There may be more, but most of these I am fairly certain have some impact on how/when the MDS works. Today I think I broke the code on low speed operation. It must be in "D" and 3rd gear to make it work between 20-28 mph. About 28 mph it shifts to 4th and immediately shuts off. I could not get it to come back on in 4th until about 34 mph, but slow back down below 30, back shift to 3rd and then put it back in "D" and the light comes back on. Kinda interesting to tinker with. I think a little experimentation will allow me to figure out how to get better in town mileage, now that I know for sure when the MDS is working and when it is not.
 

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Welcome Magnuman. Many of us visit dodgemagnum too. In fact, when you posted over there one of our members mentioned it here pretty quickly. Lots of good info here too.
 

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Hey Magnuman, thanks for the info. I read your instr. the other day and hooked my 300C up. It's set up the same way as the Magnum, and operates very similarly to the way you described. I also compared my mpg. in 4th and drive with mds off/on and noticed a big difference in mileage. At 50mph in Drive with mds on it's 10mpg better than in 4th with it off! I've also found that with the indicator I can coax the mds to come on a little more often. :)

Arnie
 

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Discussion Starter · #8 ·
arnoldw,
You got it with the "how to". At the same time I did this mod. I did the Fuel Mixture thing also. Not sure it will work as well, though. The MDS light does work great though and is definitely helping me get better mileage so far this tank. I am at about 170 miles at 18.5, in town/little rural. I am just above half so probably have another 100 miles or so to go. Don't know if it will maintain though. I just figured out the secret to 22-28 mile MDS operation though. I've pretty much got the 32-39 mph figured out and above 40 is easy. There seems to be a dead zone between 29-31. I cannont get it to work there at all. It will be nice to compare notes with someone, like yourself, that has done the mod., as I am not sure mine is working the way it is suppose to. Let me know some of the parameters as you discover them, and I'll pass mine on back. Kinda neat though.
 

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Discussion Starter · #10 ·
cmego said:
Around here most local streets are marked 30. Damn! Either have to go slower or SPEED...
Really, that's just perfect. I broke the code on how to get the MDS working from about 22-28 mph. Has to be in "D" and in 3rd gear for the MDS to work in this speed range. The trans. upshifts to 4th at about 29-30 and the MDS immediately goes off. There seems to be a "dead zone" between about 29-31 mph where I have not been able to get the MDS to work at all. You'll have to get it up to about 36-38 mph to get it to come back on. Then it's good from about 32-38 when it upshifts again to 5th and turns the MDS off again. At the slower speed (22-28) you can coax it into MDS (if it's not coming on or it's in a higher gear) by back shifting manually into 3rd momentarily and then put it back into "D". It will almost immediately go into MDS mode. If you have a lot of stop and go though, you're probably pretty much out of luck. I've driven mine on a "slow street" for almost 2 miles with the MDS on, but sometimes, in traffic, I just get it into MDS and then have to stop. Well worth doing the mod. though, IMHO.
 

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JustForFun said:
THANKS!! That was exactly what I was looking for!

NOW...has anybody done this in a 300C yet?

Thanks for the link AND the mod guys!

JFF:D
Hey JFF, I did the mod on my 300C...it's the same as the Magnum ;)
 

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Discussion Starter · #16 ·
Hey Arnold,
Have you been able to figure out any of the parameters that make the MDS work? How do you like the mod.? I am now trying to figure out if I can rig an on/off switch to turn the MDS on when I want, but not disturb the normal PCM activation of it. Do you have any thoughts on whether it might work or not? Any potential problems with the PCM, other components, DTC codes, MIL indications, etc.? Any input you, or anyone else can provide is welcome and appreciated.
 

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Hi Mag,
I like the mod, it's nice to know when it's actually working. Mine works pretty much the same as yours. I used a 15ma. green LED with switch and mounted it in the dash bezel just above and behind the cruise control stalk. I also installed an inline .25 amp fuse at the PCM just to be safe.
Everything works fine....no DTC's or MIL's.
As far as enabling/disabling the MDS, I'd rather leave it alone as it works quite well IMO. I could see potentially overloading those 4 cylinders if accelerating in 4cyl. mode.
BTW, your guidance for this mod is much appreciated. It saved me a lot of time trying to figure it out ;)
 

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Discussion Starter · #18 · (Edited)
Arnold,
I like where you mounted yours, and at 15ma it's probably not offensive at all. How tough was it to get to the dash bezel? I also like your in-line fuse idea for that extra "ounce" of protection. Your info. on the MDS is the kind of stuff I am looking for. It's hard to think of the multitude of things that could, and probably would, go wrong. So far, I am getting more nays than yays. I am still keeping an open mind though. My thought was a parallel circuit to the MDS solenoids and diodes in each cylinder's stock solenoid activation wire to prevent feedback to the PCM. It wouldn't affect normal operation of the MDS, just override it in some cases.
 

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Mag,
That bezel (or cover) is the one that the ignition switch is in. Pry the trim off around the lock cylinder, then the rest of it pops off. There's enough room in behind for the light, the switch and the wires.(I believe the Magnum panel may not be the same however)
 

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MDS Light doesn'r come on!

I hooked up the light and did the test to test the light, but the light doesn't come on! Apparently the MDS isn't working? Wouldn't this trigger a :confused: warning light on the car? My mileage mostely in town stop and go) has been poor averaging 12- 13.7mpg. Any thoughts?

Thanks
 
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