AA 1990 MJ v8 swap questions

[AA1978]

Evening gentlemen. New to this forum and not a lot of good advice on social media. but long and short, bought this MJ 5 years ago with my Pop. He’s since passed away from cancer and was a Jeep guy and machine head and passed along his legacy to me. Along with his OCD. Built a CJ and a few XJ’s thru life so I’m familiar.  Engine swaps. Never worked on an LS to AX15 to NP231 in an MJ or am I a motor guy. Bought this super clean 90, 4.0, 4wd, AC, 109k all original, no rust with intentions of turning it into my driver for my electrical contracting business. My front clip swap, suspension, brakes, steering are complete.  And I’m left with this pig of a renix with a sloppy auto trans that barely runs. Can anyone recommend a turnkey 5.3 LS that’ll fit under a stock hood operation in the northeast that returns phone calls? Novak wants 20k+ for a complete powertrain. Appreciate anyone’s thoughts 

[89 MJ]

Welcome to the forum. I don’t know if you’ll be able to find a turkey LS for this. You’ll have to do a fair bit of other work. 
 

Why not keep the Renix 4.0? They can be dead reliable and easy to work on. 

[Pete M]

can't say I can think of any turnkey packages available, but there are a bunch of v8 swaps in the Epic Tech forum you can peruse for ideas.  

 

https://comancheclub.com/forum/41-mj-hardcore-tech-epic-journeys-to-greatness/

[Comanche SS]

There are many of us who have done the LS route. Myself being one. “Comanche Fun-Runner”

Although my build is a bit more extreme than what you mentioned, these builds will be more up your alley:

Search these users in the epic forum:

@Limeyjeeper - “Comanche Dawn”

@ghetdjc320 - “Project Tomahawk”

and @70barracuda - “Driving on the street to street truck”

Are all great builds to reference also. Some of the most documented LS or LS/AX15 builds on the site.

[AA1978]

Appreciate the information. Still getting used to

this forum and how to respond. All my experience with the 4.0 in these Jeeps didn’t involve a renix system and it seems incredibly complicated, especially since nearly every line or vacuum canister is dry rotted and there aren’t many people knowledgeable on it I can bounce ideas off of. And I love the idea of LS power with a 5 speed and having this truck as my driver for the next 20 years. 

[89 MJ]

The Renix system is really not very complicated at all. If you pick up yourself a Renix Engine Monitor (REM), you should be able to solve any issue it has or at least it will give you information to post and the forum here can help you solve pretty much any problem. I don't think there is an issue that the people here cannot solve.

 

I love the idea of LS power too and considered it for mine at one point, but there is a lot of custom work that needs to be done, all of which can be shown by any of the threads listed by Comanche SS. I believe it was @ghetdjc320 that said that just the parts for a properly done LS swap will run north of $5k. If you're not much of an engine guy and would have to pay a shop to do this work, you will be way upside down in the truck financially. That's not necessarily a big deal though if you plan on keeping the truck forever.

 

You can swap an AX-15 into your truck without a ton of work if you want a 5 speed. If I were you, I would consider getting the Renix running properly (use this forum as a resource, most of us here have quite a bit of experience with Renix), swapping in a 94+ external slave AX-15, and gearing the axles appropriately to the tire size if you haven't already. Maybe you'll like the Renix 4.0, but if you don't, you won't be out much money, just a bit of time.

 

I'm not trying to talk you out of doing the LS swap. I've considered it and maybe I'll swap my truck someday in the future, but I just want to make it clear that it will be expensive and you'll have to do a lot with your accessory drive and intake manifold.

[knever3]

I thought about an LS swap, I know it would have been work either way.  I wanted to keep the stock gauge cluster and I didn't see anyone making something that would work with the pre-96 cluster so I went stroker.  If I were me then I would go LS.  Times are way different than back in 2009 though.  I would love an LS, my Renix 4.7L stroker is a dog and there's not tuning it.  Just add some injectors and adjust fuel pressure, sure you can tweak the MAP to fool it a bit controlling pulse width of the injectors, but it will never be like OBD2 or a stand alone injection system with fuel tables and such.  It has grunt, I have the 12CW crank so it revs slowly, but runs out of steam at 4k rpm.  There should be someone here that can help pick out a nice setup and piece it together for a decent price.  

 

You have to think of all the stuff you want to keep, it looks like you don't really care about stock looking, are you doing the interior swap?  I think they make an LS computer to work with the CAN bus gauge cluster of the XJ/MJ.  If you go that route it would be nice, or you can get the display for your gauges.  So many options!!!!  Motor mounts, cooling, driveshafts, nearly everything is different going LS, but if you can get a parts list to compare that will help.  The motor is the cheap part.

[Flexj]

I have a running driving LS swapped Comanche, its not the most complicated swap by any means, but as previously stated if you want it done "right" IE not having a motor poking through your hood, if you even had a hood, then yes you get north of 5k pretty quickly... Here is a vary BASIC price breakdown of what I did... 

4.8 LS with wiring harness and computer - 700
NV3500 5 speed pulled from Junkyard  - 250 
Had the NV3500 rebuilt at local shop   - 1200
adapting jeep t case to chevy trans  -  160
LS6 intake/injectors/fuel rail   - 550
ICT Accesory relocation -3 (corvette style) - 300
Camaro power steering pump and pulley  - 150
Headers  -  200
Exhaust/muffler if done yourself  -  300 
Fuel pump (spektra)  - 100
F-body water pump  - 120
F-body harmonic balancer/crank pulley - 100
Flywheel/clutch   - 250
Slave cylinder  -  75
Master Cylinder - 50
Misc AN-4 for clutch and AN-6 for fuel  - 100
Radiator amazon special 3 core with e fans (can't fit mechanical fan) - 200
Computer tuning if you can't do it yourself  - 150
OKBD Motor mount kit - 250


We're over 5200 and we havnt even gotten into fluids, consumables, tools, replacing gaskets while the engine is out, freeze plugs, adapting gauges to motor, all the misc stuff we end up getting like coil pack brackets coolant overflow res etc. Granted there is plenty here that can be cut trying to save a few pennies, but do you really wanna do a LS swap and try to save a few pennies?.. If your willing to drive with no hood or a huge hole in your hood and go with an automatic transmission I'm sure you could keep the swap below 2k, Ive done three swaps besides my Comanche on full side chevies and they are super cheap and easy to swap simply because everything fits... However then youd have to do drivelines also which is another fairly large expense. With me using the LS and a nv3500 manual transmission my drivelines actually fit right back! I was very pleasantly surprised with that one. 

My personal opinion, if you can't set 8K aside for the swap, then I would fix the 4.0... The renix 4.0 is my favorite generation, it may feel complicated but its truly the most simple reliable design when maintained correctly... Like others have said don't try to build it because its a pain to piggyback the computer, but for a stock application that is the generation I would choose. If you wanted to do like a stroker or something like others said previously I would want a OBD-2 BUS for that for the tunability... Good luck man let us know what you end up deciding to do! 

And please take my prices with a grain of salt, I'm going off of memory not receipts sitting in front of me, thats too much work for an estimate.