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4BT Cummins Diesel MJ Comanche. Will it work?

C

cbow_snow

NAXJA Forum User
Location
Southern NH
HI I just picked up a 1988 Jeep Comanche Pioneer 4x4.
It has the junk ba-10, although rebuilt 2 months ago, still junk lol, 5 spd, and a tired 4.0L 6cyl.
Has about 150,000 miles,
BUT the body is completely RUST FREE!
Which brings me to thinking, This would make a great start for a project MJ.
My main question is, Can a Cummins 4bt fit in the bay, and would it be worth it? Or should I just put an AX-15 alone and keep a 4.0 in there?
I just really want this thing to last and I know deisels are power houses and long lasting.
Now, I know that the 4bt is about as heavy as a big block chevy but could bigger springs in the front fix any sag and still perform?
Just figured I'd ask, cause i havent seen a thread on this and It just makes me wonder, CAN IT BE DONE?
 
I'd bet that a 4BT is heavier than an SBC. A 6BT is over a thousand pounds, I'd expect a 4BT to be 600 to 700. And, it's a tall engine. You'd need more than heavier springs, a lot of other reinforcing would probably be necessary.

Me, I'd probably go through the 4.0l and put an AX15 behind it.
 
cbow_snow said:
HI I just picked up a 1988 Jeep Comanche Pioneer 4x4.
It has the junk ba-10, although rebuilt 2 months ago, still junk lol, 5 spd, and a tired 4.0L 6cyl.
Has about 150,000 miles,
BUT the body is completely RUST FREE!
Which brings me to thinking, This would make a great start for a project MJ.
My main question is, Can a Cummins 4bt fit in the bay, and would it be worth it? Or should I just put an AX-15 alone and keep a 4.0 in there?
I just really want this thing to last and I know deisels are power houses and long lasting.
Now, I know that the 4bt is about as heavy as a big block chevy but could bigger springs in the front fix any sag and still perform?
Just figured I'd ask, cause i havent seen a thread on this and It just makes me wonder, CAN IT BE DONE?
Click to expand...


Its been done. There's a few videos on Youtube.
 
well, I really dont wanna have to do tons of mods to make it work. especially fab mods. im not THAT mechanically inclined i guess. id love to learn but dont have much time.
I guess i should go with the 4.0L with an ax-15. Ive heard its a rock solid combo.
Thank you guys for your input, great site here, lots of useful info.
 
It'd be more cost effective to just do an ax-15/4.0.

The 4bt, is very tall, and you have to lift it a lot to allow it to fit.

Not to mention all the fab and wiring.
 
ChiXJeff said:
I'd bet that a 4BT is heavier than an SBC. A 6BT is over a thousand pounds, I'd expect a 4BT to be 600 to 700. And, it's a tall engine. You'd need more than heavier springs, a lot of other reinforcing would probably be necessary.

Me, I'd probably go through the 4.0l and put an AX15 behind it.
Click to expand...
Jeff, the 4bt is closer to 900 fully dressed out. I like the idea but that heavy ass motor in an MJ or XJ is just too much, not to mention the lift you would need to fit it under the hood! :eek:
 
cbow_snow said:
well, I really dont wanna have to do tons of mods to make it work. especially fab mods. im not THAT mechanically inclined
Click to expand...

Definitely not the swap for you! My buddy is prepping to do this swap in his 68 bronco. He has to lift it 5.5" total so he can avoid cutting up the hood. You'll have to fab motor mounts, adapter plates, and massage some metal to stuff it in there. Not for a beginner.
 
Alright. I think im def goin with the ax15, 4.0. I have an 88 4.0, but i heard they're better after 1996, cause of the fuel system.
Is my 1988 stock 4.0 with 150,000 miles worth rebuilding or should i get ahold of a newer motor?
 
I'd just get a running 90 or older 4.0 and swap it in. It'll be the cheapest, easiest, and IMHO the best way to do it. If you wanna spend more money on the motor as in hp upgrades, etc.. start with exhaust(headers and pipes) intake swap, head swap.. and stay with your factory wiring/computer setup. You can do all the upgrades after you get it running with the replacement motor.
 
dan89XJ said:
I'd just get a running 90 or older 4.0 and swap it in. It'll be the cheapest, easiest, and IMHO the best way to do it. If you wanna spend more money on the motor as in hp upgrades, etc.. start with exhaust(headers and pipes) intake swap, head swap.. and stay with your factory wiring/computer setup. You can do all the upgrades after you get it running with the replacement motor.
Click to expand...

So anything '90 or older will pop right in? Do I need to do any mods to fit an ax15 in the MJ? Like mounts or something?
 
Go with a late model GM LS/LQ 5.3L (or larger) swap.
 
Johnnie Walker said:
Go with a late model GM LS/LQ 5.3L (or larger) swap.
Click to expand...

That would be sweet man! Im just gonna stick with the 4.0 I think, keepin it simple and reliable. I got two kids and a gf to support and still have my toy. So I wanna do all I can to have fun and still support my family.
With that swap I'd easily need suspension mods, metal fab, and axles.
Just dont have the cash for THAT sweet of a swap.
If u wanna hook me up with a donation 5.3l that would be a start.
HAHAHA lol. Just kidding, thanks for your input though.
 
I hear you on the $$$, I'm still browsing to see what I can find a deal on. I now work at a GM dealership, so we'll see what I can find. (=
You would need new susp. etc for the 4bt swap as well. BUt if you ever decide to do a swap I think the LS/LQ is the best bang for buck.
Since you are going to swap to a x-15, I would suggest converting to an external slave vs the internal that the older units had.
 
cbow_snow said:
So anything '90 or older will pop right in? Do I need to do any mods to fit an ax15 in the MJ? Like mounts or something?
Click to expand...

yep.. everything should be compatible, sensors, accessory brackets, intake, etc.. if you go 91+ you can make it work.. but you may run into minor problems getting everything all finalized.. which could cost you more money. Also.. you have a tired 150,000 mile motor ? I swapped in a motor with more miles than that in my XJ. It dosent feel tired to me.. it runs good. So, my point is you may not find a good low mile motor of this vintage, but a 150k+ could be a great running motor. Maybe you are saying yours is tired because it smokes or something ? You probably will need to get new motor mounts and trans mount as well. Very common age issue.. and you may not even know its a problem until you pull your motor and see it up close. check out brown dog for motor mounts.
 
I looked into this swap a couple years ago, and after seeing the prices on USED 4BT motors, I quickly realized that my old 2.5 4 cylinder will be just fine. Like was said, youd need to do an entire drivetrain swap to make it usable, axles and all. That and frame (unibody) reinforcement, lift, and tons of other fab work. Your old 4.0 might just need tuning up to be a good motor again. If you have good oil pressure, and good compression, everything else can be fixed. You may just need new injectors and a tune up, as these motors will run forever if taken care of.... hell even if they arent taken care of real well, they still last real well. Sounds like youre on the right track, though.
 
Thanks, maybe I just need to check it out more. I know the 4.0 is a good motor. I guess i'll be askin a lot more questions soon. Also, the motor I have needs lifters, I think the head gasket might have a small leak too. with these problems fixed, im sure i will solve a lot. Hey thanks guys so much for all your input.
 
yeah I heard stuff about renix ones being impossible to upgrade. You need a chrysler setup after 1990. also heard they are way better after 1996. is this true?
 
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