MJ to YJ Conversion Q's

[gilman711]

Hey guys (and gals). I just picked up a Jeep I've wanted for years. A 1989 MJ with a 4.0 and 5spd. I have had several XJ and YJ in past but never a Renix based vehicle. 

 

Here is what I have;

 

89 MJ 4.0 5spd 2WD

91 YJ 4.0 5spd 4WD (rolling bad frame)

 

I know I could easily swap the long blocks to HO but I'm curious on swapping the entire engine with harness and ecu. My original harness has seen better days. Also looking to convert to 4WD using the YJ parts (AX15/231 TCase and Dana 30 front)

 

Any recommendations or guidance in what I'm looking to do. I couldnt find definitive answers in my Google searches mainly on the whole 4.0 swap including ecu/harness. 

 

Thank you!

Will be creating Build Post soon!

 

 

 

[DirtyComanche]

Recommendation?  Sell the YJ junk and get an XJ for a donor.

 

YJ D30 is leaf spring...  Waste of time to use one because you need all the 5 link brackets.

 

YJ HO engine could be used, but you pretty much need a HO XJ wiring harness, so again, a donor XJ is a better choice.

 

The YJ trans has the tcase clocked at a different angle, not a bad thing but not always what people want.

 

You will need the XJ tcase shift linkage anyways, or to build your own...  Again the XJ is a better donor.

 

People pay way too much for rusted YJs, while rusted mechanically good XJs are cheap...  If you're sold on using the YJ parts I would keep the Renix fuel injection and just swap the trans and tcase in (or the whole engine too but adapt the Renix controls to it), and then part out the YJ or trade for an XJ front axle.

[kryptronic]

Plus most of the engine accessories and brackets are different XJ vs MJ.  All of what was said above by DirtyComance I'd agree with as well.

[gilman711]

I proposed YJ as I already have a YJ with bad frame/no body but complete drivetrain , harness and ecu. No gas tank either. Complete drivetrain has 88k original miles on it. 

[Pete M]

I'm not saying it can't be done, but it won't be easy.  nothing is shared body-wise between wranglers and MJs so all the components will need custom brackets, other parts won't fit or may not reach where they need to.  It'll be a challenge for sure.  maybe even fun if you're up to the task.  take lots of pictures as you go!  

[DirtyComanche]

Look into the clocking difference on the tcase with the Wrangler transmission.  If you're okay with the potential fitment issues then you might as well steal that engine/tranny/tcase and use them.  I would swap the Renix accessories onto the HO engine, and either adapt the Renix sensors to the HO intake or just throw the Renix intake on (use the Renix intake/exhaust gasket).

 

The bonus of this is you will get to embrace the superior fuel injection system of the Renix.

 

The rest of the YJ just isn't really useful.

[mjeff87]

I did the engine swap for a friend, albeit in backwards fashion.  He had a YJ that his kid blew up the engine in (got it stuck in 4LO one night and drove it home 40+ miles on the highway.......ended up ventilating the oil pan with a con rod about a mile from home LOL).  He sourced a replacement engine from an HO XJ, which I pulled and then swapped into his YJ.  Like kryptonic said all of the front engine accessories had to be swapped between blocks, which added a certain degree of difficulty to the project.  Not impossible, but extra work.