Swapping in an MDS Hemi?

[motorcitydak]

Yes, I searched and cannot find much tech, so I need help.

I want to replace my 3.9 with a 5.7 hemi and its trans. It just seems complicated by the computer. I want to have one with MDS, Ive got my eye on one local from an '08 complete with trans, wiring harness and computer. I saw only a small part of the xtreme show where they did this. I know its drive by wire so I will have to put in the new gas pedal. But what about everything else. I can do the air intake, exhaust cooling and all the mechanical stuff, but suck at electrical.

So what do I do about all the wires? I know the motor wont have an input from a speed sensor, which the PCM mite want. If I get the complete wiring harness and computer, what will it need to plug into that is not on the engine or trans? I know I can get a stand alone harness, but I want to keep the o2 sensors and the MDS. Is there anyway I can have a check engine light working? What about showing when Im running on MDS?

Does the EFI system have a return line? Will my stock pump have enough pressure, or will I be in for a custom fuel setup?

My truck is a 96 so I know the gauges are in no way compatible, but I thinking about maybe putting my temp and oil pressure sensor into the hemi so the stock gauges will still work.

I dont have many specific questions rite now because I have not brought the new powertrain home yet. But I want to start figuring everything out now...

[HemiDak]

I want to have one with MDS, Ive got my eye on one local from an '08 complete with trans, wiring harness and computer.

If you want to mod the engine later, then I suggest getting an engine without MDS.

So what do I do about all the wires? I know the motor wont have an input from a speed sensor, which the PCM mite want. If I get the complete wiring harness and computer, what will it need to plug into that is not on the engine or trans?

There will be a lot of inputs the PCM will want. Here's a few I had to deal with:

ASD relay control
Battery temp sensor
Fuel level sensor
SCI inputs/outputs
A/C clutch relay control
Fuel pump relay control
Brake switch sense
VSS #1
Transmission relay control
Transmission control relay output
Overdrive off sense
Backup lamp feed
Fused ignition switch output
ASD relay output
Starter relay control

What about showing when Im running on MDS?

I doubt it.

Does the EFI system have a return line?

No.

Will my stock pump have enough pressure, or will I be in for a custom fuel setup?

I doubt it will, but I don't know what the older Dakotas put out. I recommend using a 2004+ Ram fuel pump or something custom.

[03DakStampede]

If you want to mod the engine later, then I suggest getting an engine without MDS.


You can actually mod a MDS engine now and tune to get rid of the MDS via the Diablo tuner

[HemiDak]

Plus you still have to get rid of the MDS lifters and/or get a MDS-compatable camshaft.

[03DakStampede]

I didnt think you had to do that if you option with the diablo to turn off the MDS. I think there are a few guys that have turned it off on a completly stock engine.

[HemiDak]

That may be so, although I'm not sure it works out with aftermarket cams even with the Diablo tuner.

[Jasoon]

Yes, I searched and cannot find much tech, so I need help.

I What about showing when Im running on MDS?

...

Just to be clear, I don't think any of the MDS Rams show that you are running in Econo mode, with the exception of the 2009 models that are just now coming out...

My wife's Honda van has the MDS and shows the "econo" mode when 1/2 of the engine is turned off, but I doubt you want to swap a honda Engine into your dakota.

Read the swap info that YellowKoda has posted, it inspires us all that maybe, someday, we'll have a hemi, too.

good luck. post pics if you go down the yellow brick road.

[motorcitydak]

Thanks for the advise, but I really want to keep the MDS working. Thats part of the reason I want to do this swap

[motorcitydak]

Does anyone know of a company that can make me a custom computer and harness for one of the newer MDS 5.7s that will still operate in MDS mode?

[HemiDak]

Yeah, but all the places that can do it will charge you over $1k for it. Why not use the stock computer and wiring?

[motorcitydak]

ASD relay control
Battery temp sensor
Fuel level sensor
SCI inputs/outputs
A/C clutch relay control
Fuel pump relay control
Brake switch sense
VSS #1
Transmission relay control
Transmission control relay output
Overdrive off sense
Backup lamp feed
Fused ignition switch output
ASD relay output
Starter relay control


I would if I can adapt it to run as a stand alone setup, I have no idea how I can fake all those sensors and connections you had to deal with. I just cannot understand why the computer needs a back-up lamp feed, or a battery temp sensor. There are just too many stupid little hookups in the stock wiring. I just want the stock engine and trans to operate as they did in the stock truck, just in mine and without having all those little inputs. It will not be feeding my gauges anyway. My speedo and fuel gauge will still work. If I can adapt the temp and oil pressure sensor to fit in the hemi, then they will be fine too.

[HemiDak]

The backup lamp feed is to activate the relay to send power to the lights. The battery temp sensor is for the PCM to determine how much power it will let the alternator generate for that given temperature.

You can cut out some of the things you can get to work, but I wanted to hook up everything as best as I could, since my gauge cluster has the MIL in it. I didn't want the PCM to throw codes for something simple it doesn't really need--I wanted it to throw codes for something important.

[motorcitydak]

So do you think it is possible to make the factory computer and harness work? Im just thinking it will be so pissed off with tons of things not working correctly that it will not run. Keep in mind that there will be nothing for it to check on outside of the engine and trans.

What is the battery temp sensor anyway? Just a probe on the outside? I saw you have an optima too, so it cannot be something specific to the battery.

[HemiDak]

So do you think it is possible to make the factory computer and harness work? Im just thinking it will be so pissed off with tons of things not working correctly that it will not run. Keep in mind that there will be nothing for it to check on outside of the engine and trans.

Yeah, I think you can get it to work. I do think you'll be able to read the codes as well. You could take an OBDII port out of a newer truck and wire it in yours.

What is the battery temp sensor anyway? Just a probe on the outside? I saw you have an optima too, so it cannot be something specific to the battery.

It's a small sensor that sits underneath the battery in the battery tray. You can take one out of a newer truck and easily put in yours.

[cegpcola]

The MDS motors should be pretty much the same as far as wiring as the older Hemi. The MDS control will be in the Engine harness and the PCM mostly, so that will not require any special wiring as it would be plug and play with factory harness and PCM from the ram. The only other input that would be needed would be from the throttle, which you will have to wire up anyways. Also I have not tried it, but after looking at some of the 2003-2006ish Ram Gauge clusters, I believe that they might swap directly over to the dash of a Dakota or Durango. You might have to get the pigtails that wire into the dash, and rewire them into your wiring harness though. If this works and the signal to show the MDS is active runs through the Bus, then you should be able to see when MDSis on or not. Again I have not tried this nor have I looked at specific wiring diagrams for it, but just my observations. Why overcomplicate the swap though.

As far as modding the Hemi, the MDS motors can not be modded as heavy as the non MDS motors. To swap to aftermarket cams, you will have to replace the lifters with non MDS lifters, and if you find a MDS cam it will more than likely be less agressive then the current aftermarket Cams. Everything down to exhaust wil be a problem for you. You have to remember that the Hemi's firing order determins what the exhaust pulse is, and when you start dropping cylinders, the exhaust pulse changes and changes flow characteristics in the exhaust. It is very easy to loose power and even economy if the exhaust does not flow properly.

If you are worried about fuel mileage, then do like I did and run a non MDS Hemi completely stock. Mine is actually still running the stock Durango exhaust (modded the y-pipe to work with the Hemi), which actually creates more Back pressure and more low end torque. The Hemi is completely stock other then the aftermarket intake and a B&G Flash to get rid of sentury key (SP). This set up gets me 18-20 mpg around town, and 23-25 mpg on the highway. I dynoed at 242whp, and 302wtq, and the Durango ran a 9.70 in the 1/8th mile. Not to shabby when you consider this is all done via a stock non mds Hemi swap.

[motorcitydak]

Im not going to be building up the motor, so im not worried about that. It will have double the HP my stock 3.9 does and with a 3500lb truck, it will be enough for sure. So, I fiugre Id just rather go with the MDS


Josh-Can you Email me the PDF files you got for the hemi so I can know what the harness will need? scalabro86@yahoo.com