90comancheman Posted August 4, 2015 Share Posted August 4, 2015 I've got a 90 MJ with the 2.5 and two wheel drive that is a nice solid truck but highly underpowered. I've come across a 89 XJ with a renix 4.0 and working four wheel drive that I may purchase. Before I make the financial commitment I want to make sure this swap can be done without any major issues. I know that the renix 4.0 is not as powerful as the HO but I'm just looking for a nice driver, will the renix 4.0 do what I need, i.e.: simple towing, light hauling and every day travel duties? I've noted numerous tech articles on doing an upgrade from a renix 2.5 to a HO 4.0 but I can't find any highlighting a renix 2.5 to renix 4.0 swap. Is this swap plug and play between the wiring harnesses or would I need to remove the wiring harness behind the dash of the 2.5 and replace it with the 4.0 harness? How about the any of the other swap issues, If I go through with this swap my plan would be to swap over the entire drive train from the 4.0 XJ and put it into the MJ. Any insight will be helpful. Link to comment Share on other sites More sharing options...
Pete M Posted August 4, 2015 Share Posted August 4, 2015 If I was doing it, I'd gut the MJ and swap over everything. dash, wires, everything. you'll still need to address the rear driveshaft and rear lighting splices. by the way, the power difference between HO and renix is inconsequential. The big benefits of HO (as I see it anyway) are that it's younger and has a modern computer system. Link to comment Share on other sites More sharing options...
Pete M Posted August 4, 2015 Share Posted August 4, 2015 and take lots and lots of pictures as you go. :thumbsup: there are lots of unused plugs in an MJ/XJ so you'll want to know for sure what goes where and what goes nowhere. and download a factory shop manual for the XJ too. Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted August 5, 2015 Share Posted August 5, 2015 Check out my build thread. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 5, 2015 Share Posted August 5, 2015 by the way, the power difference between HO and renix is inconsequential. The big benefits of HO (as I see it anyway) are that it's younger and has a modern computer system. ^^ This is sort of true in stock configuration if both system are running as advertised. This seldom happens. The HO OBD1 system helps for diagnosing problems and is much more forgiving for "old vehicle" sensor wiring impedance of less than ohm that can make or break a Renix from running well or not at all. But the best advantage of the HO's are most all replacement parts are still available, and simple intake and exhaust bolt-on upgrades from later model HO engines are easy and inexpensive to do w/o interface problems. Link to comment Share on other sites More sharing options...
mjeff87 Posted August 6, 2015 Share Posted August 6, 2015 I did a 2.5/4.0 Renix swap. Pretty much plug and play, but you'll need to replace the underhood harness and ECU. Cab harness/wiring is identical through like model years. Jeff Link to comment Share on other sites More sharing options...
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