Easy way to upgrade OBD I to OBD II

Magnum Engine Swaps

  1. Wolfstar

    Wolfstar New Member

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    Hello,

    I know this site is for A bodies only but I was recommended this site by a friend at the dodgeforums.

    I have a 95 Dakota with the 5.2L and I want to do some engine upgrades (new heads and cam). Unfortunately the OBD I system has very limited options for tuning it.

    I’m considering upgrading to an OBD II harness and PCM but it looks like a pretty ugly job. Are there easy ways to do this? Anyone converted a magnum engine from this era to carb or a standalone system?
     
  2. Bobzilla

    Bobzilla Well-Known Member

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    Upgrading from OBD1 to OBD2 on a Magnum equipped truck or conversion project is easy because most of the connections are the same for sensors and outputs.
    Basically, just get an entire harness and the ECM from an OBD2 donor truck and install it on yours, then add whatever is missing, such as downstream O2 sensor.
    Take pictures of all connections on the donor vehicle as you unplug them, and maybe even use masking tape to mark each connection for where it goes or connects to.
    The biggest thing to watch is if your engine has an egr system and the donor does not, or your truck is hydraulically controlled transmission and the donor has the electronics.
    Syked ECU tuning appears to have easier to use menus than SCT, but I have not personally tried Syked ECU tuning yet. I know that SCT can turn off the electronic transmission controls.
    Finally, figure out what injector style (the connector itself) you want to run with your modifications and get a harness that has those connectors already on it, to save some work splicing or using the adapters that are available.
     
  3. DionR

    DionR Well-Known Member

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  4. 93ragtop

    93ragtop Well-Known Member

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    That would be me that sent him over here.
    My thoughts were a little different. And let me explain why.
    Wolfstar had stated he was going to be replacing his heads and cam. He also stated the AC was gone from the truck.
    Based on that, my suggestion was to go with EQ heads drilled for the LA style intake and maybe something like the Edelbrock pro flo 4. Or a carb intake , with a Holley Sniper, Fitech etc.
    My thoughts were, in the end, the self tuning systems would work better and probably be cheaper then converting and getting a Mopar System tuned.
    But again, I know on this forum there is a lot of experience swapping magnums to Carbs, LA to FI, and lots in between.
     
  5. TrailBeast

    TrailBeast Slightly Twisted Member

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    95 Dakota should be a hydraulic controlled trans, and if this is the case your suggestion is probably a good one.
    The electrical connector on the drivers side towards the rear of the trans main case will have three wires if it's a hydraulic controlled.
    If this is done there will have to be some system for applying OD and lockup.
    This can be shifted manually with a switch, by buying an aftermarket trans controller or building a hydraulic pressure switching system like I built for my Dart.

    This would apply even if he went with an EFI system instead of a carb.
    (I'm kinda thinking in Montreal the self learning EFI would be the ticket)
     
  6. toolmanmike

    toolmanmike FABO Staff Staff Member FABO Gold Member

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    Nope. Not a plug and play modification
     
  7. Wolfstar

    Wolfstar New Member

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    For this truck the transmission is the 46RH, which is indeed hydraulically actuated. I'd prefer to keep the EFI system if at all possible as it gets very cold here in the winter. I've been trying to call Edelbrock and other places but keep getting put on hold for long periods of time, so I'm already starting to question the level of support for a project of this nature.
     
  8. Wolfstar

    Wolfstar New Member

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    That is interesting. Thanks for the link.

    What would be wrong with fabbing up a custom subharness to covert the plug for an OBD I to an OBD II system, then adding extra wires as necessary?
     
  9. DionR

    DionR Well-Known Member

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    I'd bet all they do with the conversion harness is cut the plug off and crimp new ends on the wires for the new plugs. Might even be that the pins are the same and you could de-pin the OBD1 plug and stick them in the OBD2 plugs. Oh, and add missing wires for things like the transmission controls.

    So, I would say that yes, you could build a custom sub-harness to convert it. I see similar setups for all kinds of other makes, and I think there used to be one for Mopars. Trick will be finding a male plug that fits the OBD1 female plug.

    Only hang up I can see is injectors. Wiring should be the same at the ECM, but Mopar changes the injectors several times over the years, and they don't all take the same connector. Wouldn't be an issue, except that the flow rates changed over the years, so you will want to match injectors to the ECM which could require conversion harnesses to plug the injectors in. I have seen those as well, so I am sure you can buy them.

    One other issue to be aware of is the method of control for the cruise control module. It's not the module and plugging it into the ECM that is the issue, it's that the ECM has a different method of being signaled. In the OBD1 setup, the cruise switches worked different pins on the ECM to tell it on/off, set/resume, etc. The OBD2 ECM uses just one or two pins and variable voltage through the switches to tell the computer what to do. I think the way the conversion harness solved this was to add resistors into the wires in the harness and then gang the outputs to the pins as required.
     
  10. jos51700

    jos51700 Well-Known Member

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    Just rob the harness and pcm from a 96 dak, asking with any sensors that had connector changes, and you're done.
     
  11. jos51700

    jos51700 Well-Known Member

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    Mopar actions scat dak gave the basics on why they started with a '96.
     
  12. DionR

    DionR Well-Known Member

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    Might add that if cruise control was important, you might be able to swap the switched in the steering wheel and avoid the whole "resistor" fix. I think that is what the guy did on his swap in the first link I posted.

    I have a 91 Dakota that I plan to swap a 5.9 into and was looking into how to do an OBD2 swap at the same time. My steering wheel won't allow for swapping the switches and (as I recall) I can't swap wheels either. Thus the research into how it worked.

    In the end, I am going to just convert to a '95 or so ECM for the 5.9, which has it's own share of problems like a returnless fuel system on the 5.9, change to the speedo output on the trans and no speedometer cable so the need to convert to a 95 instrument cluster with it's associated pin changes.
     
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