Stand alone 4.0 for J-10

I just lucked into a fairly nice 82 J-10. Would like to pop a 4.0 in it to replace the 4.2. I know I'll need the wiring harness etc...but what will I need to make it run? Do I just need power for the computer and starter power? Looks like wiring on a 98 goes into the fire wall in 4 places? Has anyone wired one to stand alone before? Didnt see anything on painless wirings web site...should I keep the J-10's auto tranny and 208 tcase or should I put everything from a xj in it?

ummmm, not a bad idea, eventually thats what my xj will be, but im going the other way, starting complete and removing what i dont need/want

Just off the top of my head you will need to address the CPS issue if you use the J10 tranny. I would use the XJ tranny(AW4) if possible, its strong and gives you an OD with TC lockup. It might even bolt up to the NP208, if not use the XJ NP231 with a SYE kit. But to use the AW4 you would have to convert to a floor shift.

BTW the older you go for a 4.0 donor the simpler the wirring gets. The old renix system is pretty simple but any system will be more complicated than just putting power to the computer. All of them use o2 sensors and map sensors as well as monitoring enginge temp and knock.

I can handle all the under hood wiring and sensors fine, its just the wiring that goes in to the xj fire wall that will hang me up. :rattle:

CJ 4.0 swap forum

I found this last night will searching for about an hour. damn I'm tired, been working loooooonnnngggg days...

I really just need to find out what passes through in to the inside of the xj that i need to hook up to make it run. guess I'll have to wade through this cj forum for a while to find it but it seems like they've done this a bunch.

Why?Considering the J-10 is about 2000lbs heavier than the XJ,I think it would suck the life out of a 4.0 and burn the AW4 to the ground.Ive had 2 J- Series trucks and would never own another one.

^^ If it came w/ a 4.2, A 4.0 would be just fine. Im sure the AW4 could handle it, its a good tranny. The yota guys rus it in their 500+ HP Supras without incident.

I would go this route:

http://www.4wd.com/shop/productdetail.asp?c=8&model=cj&subcat=&division=5&category=313&productsku=P5249686AD

It might seem like it costs more up front, but I think would be a better fit for the J-Truck and give you a lot fewer headaches. You could retain the extra cubic inches, and it would not neccesitate any changes to the current transmission and transfer case.

Littlewhitexj said:

^^ If it came w/ a 4.2, A 4.0 would be just fine. Im sure the AW4 could handle it, its a good tranny. The yota guys rus it in their 500+ HP Supras without incident.

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Just because it came with one from the factory doesnt make it right.I had a 327 in one and a 360 in the other.Gutless on a flat road and WORTHLESS on the hills(especially with any kind of cargo load).

RCP Phx said:

Why?Considering the J-10 is about 2000lbs heavier than the XJ,I think it would suck the life out of a 4.0 and burn the AW4 to the ground.Ive had 2 J- Series trucks and would never own another one.

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Hey Travis.


Considering his J-10 has the 258 in it...the 4.0L would be a nice improvement overall.

And the J-10 does not weigh anywhere near 2000 lbs more than an XJ. Curb weight for the J-10 is only a hair under 4,000 lbs. On an XJ it's right around 3200 lbs..that's only an 800 lb difference.

If memory serves from the MJ swap we did...as long as you have the interior harness it's cake. Just a matter of literally 'running' the wiring. Basically the ignition and whatever other sensors it has that are part of the interior harness are all you'd need. Your best bet is to just have the ENTIRE harness. Under hood (ECM), interior, and the power dist block harness. Should be 3 separate harnesses depending on year of the motor you use. (2 harnesses at least).

And while we're at it...why not take the 258 apart and stroke the 4.0??

I dont have time to stroke it. Heck, we were checking out the motor in it today a bit and seems that it may have been rebuilt and has a newish carb. Maybe propane? I dunno...4.0 swap would be nice. Give in an xj heart and some 4.56 gears?

Well shoot...it's not like you don't have the motors lying around...why not let's sit down and piece together a MPI setup for the 258? Don't have time...hah! LOL...you'd have time if you really wanted to.

yellowxj said:

I dont have time to stroke it. Heck, we were checking out the motor in it today a bit and seems that it may have been rebuilt and has a newish carb. Maybe propane? I dunno...4.0 swap would be nice. Give in an xj heart and some 4.56 gears?

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check out the XOTA thread - that guy did what you are talking about - only put the cherokee driveline into a toyota pickup...
http://www.naxja.org/forum/showthread.php?t=69712&page=1&pp=30

yellowxj said:

I just lucked into a fairly nice 82 J-10. Would like to pop a 4.0 in it to replace the 4.2. I know I'll need the wiring harness etc...but what will I need to make it run? Do I just need power for the computer and starter power? Looks like wiring on a 98 goes into the fire wall in 4 places? Has anyone wired one to stand alone before? Didnt see anything on painless wirings web site...should I keep the J-10's auto tranny and 208 tcase or should I put everything from a xj in it?

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I already have a 4.0L from a '93 Grand Cherokee (along with the only year AW4) in my '84 J10. Get a '91 to '96 4.0L EFI system to put in as it's easiest to wire. (all under the hood!) The earlier Renix one will work but with LOTS of extra wiring work! (the computer is in the cab and sensors go all over the place! The '97 and newer XJ one is integrated with the whole harness and PCM computer) Get the CJ V8 conversion 3 core rad (I forget the part number, but the hoses are placed the same as the 6 cyl) for cooling. Since you have a post '78 steering box, you can rebend the XJ lines to fit (O-ring type) Use the 258 6 cyl motor mounts and frame horns (different from V8) and keep the XJ accessories (don't know how the AC will work yet) except the offset fan. I'm using the ZJ fan and pump setup which is centered. So is TJ and late YJs.
The best reason to not run a ZJ setup is the PITA alarm system needs to be bypassed somehow (I tried for 3 months, but my brain is too muddled from a car falling on me in '95 to figure it out. I even bought the factory CD!)
The hardest problem is the brake booster. I have a GM Hydroboost that is getting mounted upside down (to clear the intake) and my motor mount pads are Energy Suspension 6 cyl CJ ones.
Wish I could get at my Jeep to start working on it! (it's buried at the back of a 10' by 30' storage with all my extra parts in, on and around it!)


Oh yeah! The J10's 258 made @135 HP. The HO 4.0L makes close to 220 and my stroker I am building (to run on Propane) will be @280 HP with tons of wheel torque and 4.10 gears with 42" tires makes it the same as stock with 3.08 gears and tires in third (AW4) and the 4:1 tcase will let me churn a little mud with all 4! (ARB front and rear baybee!)

Thanks for the info...great to know its been done. Sounds like something I'll be starting into soon.

I would keep the tall gearing till you decide what tires you are going to be running. I put 4.10s in my '87 Comanche and it SUCKED all the power out of it! (and that's with 33" tires!) The power band is in the low RPM with Renix rigs. I have 3.73 and it works just fine . I even tow FSJs around with mine (clutch is getting a little toasty now after almost 90,000 miles)

You know whats funny my 03 Tundra with 295hp and 314lb of torque has a aw4. Looks just like a jeep trans with a different bellhousing and transfer case adaptor.

Lexus has them in their V8 powered SUVs as well. AND they are in Landcruisers with turbo diesels too!