I have a complete drivetrain from a donor 1994 cherokee, 4.0/ax15/np231, engine harness, fuse box, and computer. I plan on dropping it in my 94 yj that currently has a 2.5/ax5/231. I've done some extensive searching, but my results have been scattered. I know about moving the frame mounts, and clocking the transfer case. Mostly I'm concerned about the wiring, not sure if I should use the XJ harness, or splice in the two extra injector wires and plug the XJ computer in and be good to go. Just looking to smooth out wrinkles before i begin the tear down. Any help would be appreciated.
Wiring is so easy.
Take a few donor wires from the Cherokee ECM plug and add them to the YJ. Much easier than swapping harnesses.
Overall transfer case will end up about 2 1/2 inches further back then the 2.5, so make sure you double check that it won't be compressed too much.
I have an sye and a driveshaft for the tcase, so that doesn't really seem like a big issue to me. some say fuel pressure will be an issue, others don't even mention it at all. Like I said before, just trying to get all of my ducks in a row before I pull everything apart, as my jeep is my DD. Hoping this will end up being a solid reference thread for people doing similar swaps.
I used an engine from a 98 TJ for my 2.5L swap, and I had to change out the fuel rail. I'm not familiar with the XJ fuel rail, but you'll want to use a fuel rail with the pressure regulator on the rail (it'll look just like your 2.5L fuel rail, but longer). It'll have a gas inlet and return line on the rail. And you'll want to get injectors to match. If this isn't clear or if you need pictures, just let me know.
Fuel pressure regulation might be an issue...didn't the XJ have regulation in the tank like a TJ? If so, the fuel rail swap is the easiest solution.
You'll also want to make sure the injectors match your fuel pressure regulator
A few different options if it isn't regulated at the rail. On my CJ swap I ran an external pump (but would work with internal as well, combined with a WJ fuel filter which has a regulator built in and then run return line to stock return line.