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Motor Swaping With 86 an 90 MJ... WILL IT BOLT UP??

MJEEPMAN

NAXJA Forum User
Location
Kentucky
I own a 86 MJ thats I4,TBI,4 Speed Manual, and 4wd. I am looking at buying a 90 MJ that I6,FI,Automatic, and 2wd. My question is will my 86 drivetrain allow me to bolt up a 90 I6? And does the wire harness on the I6 an Automatic have anything important runing into the tranny?.. Or Will there be other things I need such as... Wire harness from I6,AT, and 2wd to I6,Manual, and 4wd... PLEASE HELP!!! THANKS
 
In short No. That would be a major undertaking. Firstly the XJ/MJ engine compartment changed in '87 to accept the 4.0, the I6 won't fit in your engine bay without major modifications. You'd need the entire I6 wiring harness including the engine and transmission controllers. Your five speed won't bolt up, your t-case may or may not mate up to the auto but even if it will (I don't think) it's the much less desirable NP207. Also the TBI injection on the I4 only runs at about 17psi whereas the I6 multipoint system runs in the 39psi range, so you'd need a fuel pump as well (I have heard that the TBI pump will run the MPI system but it wouldn't be ideal as the pump would be working well beyond it's intended flow rate). Don't get me wrong it is do-able and some on here have done it I think. If you think you might be up for tackling a project of this magnitude the information you need is defineately on these forums do some searching and if you've still got questions I'm sure somebody here knows the answer.
 
I did the 1-4 to I-6 swap. While it has a few steps, it is definately doable. You end up swapping the front radiator support and the hood. You also have to peel off the side supports where the headlights feed through and swap them from the donor. If you are good with sheetmetal, it is a 2-3 hour job. You end up moving the firewall back about a half inch with a BFH at one small spot. A two minute job.
 
The reason I want to convert my 86 to I6 is because it is in the best condition that I have ever seen a comanche. Plus I have recently added a 6 in lift an 32 in tires and want more power!! lol Like I am sure everyone on here wants!! But thanks alot for the help!!
 
Okay that makes sense. Aside from the complications from the differences in the engine bay I was going to try a similar project myself. I have an '89 2.5 5spd 2wd MJ that I was going to convert to 4wd and then eventually swap in a '91 4.0. I only abandoned this project because I found a cheap MJ that was already 4.0 4wd. I still have almost as much work to do though as this truck has major engine compartment wiring issues and the trans an t-case are far from what I want in it (3spd t-flite, NP207). I encourage you to do what it takes to get your truck the way you want it. The swap shouldn't be that bad if your buying the whole '90 truck but you'll be swapping over a lot of wiring and such. As I said though you can't keep your manual, it won't bolt up to the 4.0. So, you'd either need to find a suitable manaul trans or the 2wd auto can be used if you can find a t-case and a tranny output shaft I think. One bonus is your axles, they are the same as what would be under a 4.0 4x4 except that they are 4.10 gears rather than the 3.07's or 3.55's of a 4.0. The 4.10 gears would work nicely with a 4.0 and 32's. You will also need new driveshafts, which brings me to a question. Can you measure your rear driveshaft for me? I'm selling the 2wd MJ and if the buyer is interested I have most of the parts for the 4wd conversion excluding a 4.10 geared front axle (I have one but they can't have it) and a rear driveshaft. I've never come across a 4cyl 4wd MJ and the parts came from an XJ so the rear shaft won't work, I'd like to be able to tell them what lenght rear driveshaft they would need for the swap.
 
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