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86' 2.5 to 87' 4.0 swap?


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Ok, I am new to jeeps and just picked up a pair of free ones. I got an 86' MJ with the 5spd and the 2.5 (blown motor) and an 87' Cherokee with the 4.0 and auto tranny. I want to take the 4.0 and put it in the MJ. How much of a pita is this going to be? I assume I'm going to have to switch most, if not all of the wiring. Also, how do I know what kind of 5spd the MJ has? I know the ax-15 will bolt to the 4.0, so I' hoping that's what I have.

 

I have wrenched on a lot of stuff, just never jeeps before, so I'm not afraid of doing a swap, I just want to know what I'm getting in to. Thanks a lot!

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86 makes more problems than most as the 4.0 was never available in it. You have to change out everything under the hood including radiator supports and maybe even the hood prop. Firewall may or may not need to be massaged <1" with a BFH.

 

Never done it myself, just repeating information that has been posted before.

 

You will also need all under hood wiring, possibly dash wiring.

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So I'll need all the wiring and the gas tank/sender from the cherokee, and to source an AX-15 (cause auto tranny's are terrible) and that should be it (besides the million things that nickel and dime every project to death). I'm hoping these things are as easy to work on as subarus and toyota 4x4s haha

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So I'll need all the wiring and the gas tank/sender from the cherokee, and to source an AX-15 (cause auto tranny's are terrible) and that should be it (besides the million things that nickel and dime every project to death). I'm hoping these things are as easy to work on as subarus and toyota 4x4s haha

 

 

yup. aside from obviously the engine, cooling system, and other associated necessary parts.

 

you won't be able to use a cherokee gas tank in the stock location BTW...just won't fit. you could go the simplest route here and just get an aftermarket in-line fuel pump and filter and cut them in under the cab.

 

 

you're going to need the 87's entire front core support. this includes the front cross-member, headlight bucket supports (the metal behind the headlight buckets), and upper radiator support. this will require drilling spot welds out on the donor vehicle, and spot-welding them in (after removing the old junk) to the 86. you'll also need the 4.0 hood because the hood latches are different and not interchangeable.

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you need every little part from the 4.0 to swap into the MJ, including gas tank and fuel sender and likely fuel lines.

 

No, you can re-use the stock MJ gas tank, and sending unit, and fuel lines up to the frame mounted fuel filter.

 

What you need to do, is change the in tank fuel pump, and you can use the donors (XJ 4.0) fuel pump, in place of the MJ's 2.5 fuel pump. This it the only difference between the 2 engines, is the psi of the fuel pumps.

 

The MJ's sending unit will work, because your donor is a Renix era electrical system.

 

Everything else that was stated is true, radiator support, radiator, hood latch, and you might even want to swap over the hood itself.

 

Also, the engine mounts will need to be changed. The tranny mount will need to be changed.

 

The complete engine bay harness, and the dash harness will need to be changed, along with all the senors, and ECU.

 

You didn't state if both of these were 2wd or 4wd??

 

You'll need to have the rear drive shaft shorten if your switching from manual to auto.

 

The brake pedal assembly also need to be swapped out, from the manual to the auto.

 

In a nut shell.......every little part from the XJ's 4.0 will need to be transfered over to the MJ. The most important thing is......you have the vehicle there with you, so the swap will go smooth.

 

The only snag you'll run into is the interior harness, leading to the rear, that needs to be spliced in to the correct MJ wires.

 

An easy way of doing the interior harness is, if the donor's dash is in good shape, swap the entire dash over, it's a direct bolt in, and all the connectors are plug and play.

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you need every little part from the 4.0 to swap into the MJ, including gas tank and fuel sender and likely fuel lines.

 

No, you can re-use the stock MJ gas tank, and sending unit, and fuel lines up to the frame mounted fuel filter.

 

What you need to do, is change the in tank fuel pump, and you can use the donors (XJ 4.0) fuel pump, in place of the MJ's 2.5 fuel pump. This it the only difference between the 2 engines, is the psi of the fuel pumps.

 

The MJ's sending unit will work, because your donor is a Renix era electrical system.

 

 

the comanche and cherokee fuel pumps aren't the same size, from all of the ones I've looked at. the cherokee one was half the size of the comanche one...thus not swappable.

 

I suppose there would be no reason for the tank not to work.

 

the rubber lines coming from the fuel tank to the hard lines should be replaced...it is old, and also not rated to the pressure of an H.O. pump.

 

 

You can just pick up a comanche pump from someone on the club (I should have several), or you can buy a new pump, and pop it on the 2.5 sending unit. IIRC the fuel level sender's float is different between the 2.5 and 4.0, but it should still work.

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the comanche and cherokee fuel pumps aren't the same size, from all of the ones I've looked at. the cherokee one was half the size of the comanche one...thus not swappable.

 

The Renix era fuel pumps for the 4.0L XJs and MJs are the same. The 2.5L XJ and MJ pumps are different, although I don't know exactly what the difference is. Probably size. :dunno:

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why exactly does the core support have to change? I'm mostly asking because the cherokee is a rust bucket, and the MJ is clean.

 

 

to make the radiator fit. there is zero way to make the 4.0 radiator fit in an 86 without swapping the core support. it also is what the 4.0 hood latches mount to. it's really not hard...like 13 spot welds each side. and before you ask, nope, can't use an 86 radiator or hood at all...the 4.0 wouldnt even fit with where that's positioned in the engine bay.

 

as far as the front crossmember, it is the lower mount for the 4.0 radiator. you could probably leave your 86 crossmember in, and weld risers with brackets on that for the 4.0 radiator to mount.

 

 

if you're worried about paint on the hood, you could *theoretically* cut the notches for the 4.0 hood latches out in it and tap the two mounting holes for them, without affecting the outside paint (if you're careful).

 

then you'd just bolt the 4.0 hood safety latch to the 86 hood...and yes, that part is a bolt-on.

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ok, Thanks for the info about that. I'm not worried about the paint, because my wheeling rigs have a tradition of Safety orange paint haha. I'll be picking up my donor XJ tomorrow hopefully, so I can start to strip it down and see if that front core support is useable. I'm sure I'll keep this Thread active as I go, hopefully with pics.

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