Comanche 2WD to 4x4

Hi guys, I aquired a 88 2wd MJ for pracrically nothing and have always wanted to convert one to 4x4. I got an AX-15 with a NP231 Tcase out of the junkyard for cheap. Did the spring over on the rear with a Chrysler 8.25 and the front axle from a Cherokee bolted right in.Put a Rustys 4.5 set of coils on the front. The guy I got it from said the 4.0 had a blown head gasket which in reality was a busted block. I got a 99 model 4.0 with 77k on it and and my question to you guys is can I run the renix stuff on this motor? IE intake, distributor I don't really want to tackle the wiring conversion if I don't have to. Any advice would be appreciated. Thanks, Mark

no an MJ is spring under, but its not that hard to cut off spring perches and weld on new ones. Also pretty sure that ax15 and 231 will bot right up to your 99 motor.

I have no experience running a newer motor on old equipment.... but I am pretty sure all 4.0 Blocks are basically identical save for a few extra sensor holes, etc. So im betting you can run the 99 block and HO head with all the rest of your RENIX stuff.

Already got the rearend under the MJ. Not only are the perches opposite from an XJ, the width is different too. The trans came from a 98 Cherokee with a 4.0 so I'm pretty confident it will all go back together. Right now my biggest concern is making the late model motor work with the Renix stuff. So far I've noticed the timing chain cover will have to be swapped and one of the holes on the drivers side of the block isn't drilled and tapped for a coolant sensor. No problem on that though, one right behind it had a plug in it.

That guy was a wealth of info wasn't he? I have nothing to add either, so this is just as useless to you. Back to the beer.

Stallacrew said:

Why somebody would want to do this is beyond me...........

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:yelclap:

it would be better to grab the harness and computer out of the same year range as the donor motor. this would increase horsepower from the RENIX crap. it is legal in most if not all states because your putting a newer motor in an older vehicle.

if the price was right for me i would love to get a 2wd MJ and convert it to 4wd as my DD.

Don't have to really have to worry about the legalities here, we don't have to pass any emissions or state inspections. I just wanted to know if it was possible to run the old stuff for awhile. Probably do the wiring upgrade in the future.

I recently had a shop swap a 99 4.0 into my 87 MJ. I asked about the wiring issues and they said its possible to use renix wiring/computer with the 99 motor, but its very complicated. Lots of splicing, testing, re-routing and what not.

It was WAY WAY WAY easier to just swap all the stuff out of the 99 into the MJ.

I got really lucky and found a very nice 99 XJ that had front end damage. I got the whole thing really cheap and the shop swapped everything over. My truck runs awesome now.

If you plan to do the wiring swap sometime in the future .... just do it now - you will be so much happier you did.

It's really not that complicated actually...

Coolant sensor locations are different. Big deal, swap em around and lengthen/shorten wiring harnesses as needed. They are all one or two wire resistive sensors, you have to really screw up to make it not work.

All the other sensors should bolt up just fine. Take off one RENIX sensor at a time, install it in the 99 motor. You won't have a spot to screw the anti knock sensor into (back passenger side of the engine) so either leave it hanging or tap a hole for it, I believe the hole is still there but not tapped. Careful you don't drill into an oil passage or coolant gallery.

The biggest issue will be exhaust/intake manifolds. I believe the intake manifold will match up fine but the exhaust may not, compare the ports in the head and manifold to the gaskets for each year. Your throttle body and manifold sensors are different from the 91+ ones; you will have the easiest time if you simply bolt your intake manifold on but may have to swap your head onto the 99 block for this to work. If your head is fine, go for it.

A few block mounting points for the alternator, AC compressor, PS pump, and idler pulley may be different - I suspect the lower rear mounting point for the idler pulley bracket will be a different height, but can't recall with certainty. Mix and match em till things line up and find a belt that fits.

It's not really rocket science, just a bunch of silly small things.

EDIT: a few other things - rear driveshaft needs changing, as I'm sure you figured out. You may have to modify the harness to make the reverse lights and/or part-time light on the dash work properly, but it's all 12 volt DC light wiring, find the right switches on the TC/tranny and in the wiring harness (check your FSM or Haynes) and splice em and you are done.

Thanks for the info guys, one more thing I ran into is the distributor clamp hole location is different on the 99 block, I think I can just backup 1 or 2 teeth on the cam gear to distributor gear and get the rotor back on #1 on the cap. Everything else seems to be working so far.

stewie said:

this would increase horsepower from the RENIX crap.

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you have no idea what you're talking about.