IS IT EASIER TO SWAP OUT THE ENTIRE POWERTRAIN OR JUST TAKE THE 94 HIGH OUT PUT HEAD / WIRE HARNESS AND USE IT ON THE 89 4.0 BLOCK  

Do you have the '94 vehicle complete?  

i have the complete 1994 donor vehicle  

Definitely use the engine wiring harness, including the computer from the '94 and swap the whole drivetrain. I'm not sure the swap would be worth the effort if it's just about performance of the HO vs the non HO.  

i just thought that swaping the ho head / updated injection ,wiring harness & computer would be basically the same h.p. and output of the 94 without having to pull an entire motor out.
im new here...just looking for some easy solutions
thanks.
anchorage , alaska  

Chasing down the gremlins by mixing and matching is very frustrating. The more complete the swap the less gremlins. I'd think you could pull the motors in about the same time it would take you to remove two heads, clean one up and reinstall it. The first motor might take all day, but the second would take an hour or two.  

Also, the '89 has Renix (crap). It is a Renault engine management system. Some really hate it and go to great lengths to get rid of it. If you'd said "get rid of my Renix", my answer about effort would change. But how to go about it would not. Do it complete. There's too many little things that could get you. Also, think about emission testing. Is that going to be a stumbling block?? Meaning if you don't get it just right, it won't pass. Sometimes it is hard enough to get the check engine light to stay off when everything is compatable (looking for that gremlin). That is why I asked if you have the whole '94 vehicle. That way you can take everything.  

Also the cam shafts are different between the engines. The fuel maps in the newer computer woud not be in sync with old cam profile. Swaping the cam would involve some doing also. The cam bearings and the lifters are matched and broken in with the specific cam. The lifters are broken in to their respective bore locations in the old block. So, you would at least want to install new cam bearings and lifters. When lifters get re-aranged, cam lobe failure could result.  

your points are well taken.alot of issues i had not even considered ! thanks a bunch for your knowledge and input.
i'll definetely use the 1994 donor jeeps complete drive train and electrical.
sincerely ron davis
anchorage , alaska  

The newer computer and wiring harness and head will work on the older 4.0.

It won't be right, it won't make as much power as the 4.0, but it will run.

I'm in the middle of updating a 88MJ to 97-up XJ stuff, and its a bear.  Awol, why are you looking at doing this in the first place?  I guess that's the first question I'd ask.  I mean if the Renix vehicle is running, do you really want to completely strip two XJ (I'm assuming they are both XJs) and rebuild one of them?

I don't know about 88 to 94, but I know from 88 to 97 everything changed.  Hole locations in the firewall for fluids, pedals, heck, even the HVAC unit are all different.  I'm going for that "out of the factory" look, so I'm probably being more detail oriented than needed... but there is a bunch of stuff that I am sure will pop up unexpectedly.  

I remember back to my first swap when I was 16. A Mazda with a Rotary converted to a piston engine.

Boy did I learn a lot.

The nice thing was that the car wasn't worth any less after I got done with it. Still about 200 bucks. I drove it for two years and the girls loved it. At least that's what they said at the time.

Anyway, enter into it with the right attitude, you'll learn a lot. It won't be a piece of cake but you'll be able to hang your hat on it. Or maybe up there you have some Moose horns to hang your hat on.  

basically,i was just trying to update it a bit.whenever i try to buy up grade engine parts ,there is never anything really avilable!
i dont care about perfection as far as the firewall holes go.
my xj is a 1989 full fledge convertiable,that i cut the top on.it has a black canvas top to cover it.
its painted o.d. green with a big white star on the hood.side mounted jerry and ammo can.full roll cage
desert rat black stenciled onthe door from when i lived in arizona.and xj1989 on the fenders.o.d canvas front and rear quarter panels.it was in 4 wheeler mag back in approx. 1990.painted black--they called it a cheromanchee.i lived in california at the time.
thanks guys.  

Wow! Definitely do it. It sounds like a lot of fun. I'm in Phoenix and have visited Alaska. People here know how to get crazy, but people in Alaska know how to be free spirits. Have fun!