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4.0 Swap ?


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Hi new to the fourm and my 88 lwb mj. It has the 2.5l in it now but its been ran hard and the ax5 is starting to make some noise. I am wanting to swap in a 4.0l ,aw4 setup. I am wondering if you guys can give me some info and insite on what all would i half to change if i went with a motor and trans from a 97+ xj. I have been told that i would need to change the hole dash and heater setup to do it. Is there any truth to this? Any help or info would be great

Thanks

Ben

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The short answer:

 

Complete "bastardized" (High Output to Renix) wiring harness.

Shortened driveshaft.

Firewall massaging to fit the 4.0.

Radiator supports for the 4.0.

 

IIRC; there should be many topics on this if you search through the tech forums.

Also, sorry for X2 post.

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I have done some searches and none of what i find are useing the obdII system from a 97+ xj. I also read that the fire wall was changed in 87 mj and no fire wall mods are needed

As far as radiator i would be using the support from the donnor and building a drive shaft is no big deal.

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If youre changing from a 4 cyl, to an 6 cyl, youll probably need to pull the dash anyways to swap computer wiring. That and there are also differences in regular dash wiring between years as well, with different connectors and pin locations... etc. The dash isnt that hard to pull, and once its out, its nothing to swap the HVAC box seeing as how the coolant is drained already anyways for the engine swap. That will also give you a chance to clean the thing out as they get pretty dirty over the years. When I swapped mine out for adding AC, it was full of mouse house and what have you. I cleaned it all up and doused the whole thing with Lysol to make sure it was all disinfected. I also cleaned up the blower motor and lubed the bearings in it at the same time. If you can swap anconvert engines and such, pulling a dash is nothing. You can keep the same outer dash, just change the electronics underneath and update as much of that as possible with your newer donor. If you get a 96 plus, youll have OBDII, and easier diagnostics for later on. Seriously, its not that much more work to do it all the right way the first time instead of trying to match up stuff piece by piece. Let us know what you figure out! And good luck!

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Since you are starting with a 4 cylinder MJ, you might be better off using the "BIGHEEP Method"

http://comancheclub.com/topic/36506-semi-ho-swap/#entry365458

 

 

Nope, you can use the same under dash harness. You just have to repin the blukhead connector to match the MJ. I swapped a 93 XJ 4.0L into my 1988 YJ with a carbed 4.2L and I used the same under dash harness. You can actually swap in the new engine, hook up the fuel and get it to run by just splicing in 5 wires.

 

^^I haven't done a harness match up swap like BIGHEEP did,

so he'd be the best to ask,

but would assume the way to start would be with a 91-95 engine (easiest to swap) & under hood harness/computer.

Seems like you could get it to work without the HO gauges,

but I'd also want to grab the 91-95 XJ gauges & a 91-92 MJ fuel tank sending unit (otherwise your gas gauge will read backwards)

 

 

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ok thanks for the info on this so far. the repinning of the harnes shouldnt be a big deal as long as i can find the pin outs for both (Its what i did to put the mpi on my cj) the other thing is finding a donner in my area that i can afford. does anyone know what all problems would i run in to using a zj as a donner?

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You wouldnt have all necessary parts if you use a ZJ as a doner. The reason you find an XJ is so you can get the radiator, the core support, and all the correct placed and length wiring. That and youll have a bunch of other spare parts and possible upgrades as well. Most XJs had power windows and locks, so that might be another possible upgrade for your MJ on top of getting the drivetrain. And the 97 up models had one peice door windows and better mirrors. This is something you could do in a weekend after getting all the other stuff done, and if you do the whole dash and dash wiring, it would be plug and play! If you want a NP242 transfer case too, youll need all the shift linkage from the donor as well. Full time 4x4 would be a nice upgrade and a reselling point if it ever comes to it. A whole XJ is just a better option for doing this, theres no other way around it. Why waste all time repinning harnesses when you could just swap it in complete and be done and ready to go? Just sayin. It would save you a ton of headaches later on doing it this way.

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  • 3 months later...

ok so I am moving forward on this and  have picked up a 98 Xj. there are a few questions that I have before I start pulling parts and one is the fuel pump/sending unit. I seen somewhere on here that I can cut a hole in my gas tank to drop in the 98 pump using some ring but can't seem to find the ring anywhere. the other is my mj has crank windows and I am not sure if I can use them with the new dash any info o these would be great. Thanks

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Here's a tip from a fairly new comanche owner/comancheclub member: Head over to the "Your Project MJs" section and read a few of those builds thoroughly. We will always assist you if needed, but a lot of those threads will give you a lot of knowledge and a majority of them contain an engine swap of some sort.

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The ring I bought. However, I never liked the way it all worked. I could only use about 3/4 of my gas tank because the pickup for the fuel pump doesn't reach the bottom. What I did was replace it with a Dakota 22 gallon tank and pump/sender assembly. The fuel gauge reads more accurately, reaches the bottom of the tank, and gives increased capacity. There are a few threads floating around here on the subject. I also have some highlights in my build thread I think.

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ok so motor mounts? it looks like there is two sets of holes on the frame that they can be bolted to but do I need to move them or not in the link that 87warrior put up there is a pic that shows the mounts and mine look to be in the same spot. but I am not sure if that is right or not. any info on this guys?

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  • 7 years later...

I am doing the swap I have a 89 mj with a 2.5 and a manual trans. I already have the doner vehicle 95 xj sport with a 4.0 ho and a automatic trans. I am deep in this project already. I got the motor and trans pulled from doner and the motor harness , dash and plan on keep going after reading yalls forums. Any thing else I should know about this swap like anything tricky about these years, or models ?

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