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cheapXJ give us the lowdown on your 2.5 to 4.0 swap!

rockwerks

NAXJA Forum User
I may have to do this this weekend in my 2x MJ and would like to know what IM up against I have a complete 87 XJ to get parts from and will be swapping 2.5 ax4 2x to 4.0 aw4 4x

TIA
 
xjnation said:
I may have to do this this weekend in my 2x MJ and would like to know what IM up against I have a complete 87 XJ to get parts from and will be swapping 2.5 ax4 2x to 4.0 aw4 4x

TIA

I've done the 2.5L to 4.0L (4.7L stroker) swap in an 85XJ. What year is your MJ?

Lots of things vary depending on the year models.

There are clearance issues and electrical issues. On an early XJ, you have to use a BFH and move the firewall back at a single point on the drivers side rear of the engine where the exhaust comes out of cyl #6. No big deal, there is nothing behind the firewall. On the early XJ, the hood is held down with a single hood latch. In order to use the longer motor the radiator has to be moved forward. This means that the whole front radiator support as well as the welded in sides that hold the headlights has to be changed. I even had to make a support to hold up the radiator since the front crossmember under the radiator is different. Good news, the 4.0L motor mounts just bolted up to existing holes. Once you move all the front sheetmetal then you have to swap the hoods.

In order to simplify the whole wiring thing, I recommend pulling the complete dash with wiring from the donor. That would include the fuse box. Then pull the complete under hood wiring as well. I did a harness patch when I went from carb'd 2.5L to TBI 2.5L. It was a pain and I know vehicle wiring and had both manuals.

When you pull the complete dash, don't forget the tranny computer behind the passenger side dash lower panel.
 
old_man:

I'm going from an 88XJ to an 88MJ so I should run into the same clearance issues you had.

I am more concerned with the wiring compatibilty between the 2.5 and 4.0 harnesses - swapping the hard parts will be easy enough for me I think, but getting the wiring and engine control correct might be beyond me.

Chris
 
NHXJer said:
old_man:

I'm going from an 88XJ to an 88MJ so I should run into the same clearance issues you had.

I am more concerned with the wiring compatibilty between the 2.5 and 4.0 harnesses - swapping the hard parts will be easy enough for me I think, but getting the wiring and engine control correct might be beyond me.

Chris

If they offered a 4.0L in an 88MJ, you should have no sheetmetal issues other than the radiator, I would think. Does your MJ have one hood latch or two.

As for the electrical swap. That should be a walk in the park. Pull the firewall master connect plug that is on the drivers side just under the clutch master cylinder. Compare it to the one from the other vehicle. If they are the same shape, you should be fine. They standardized on the wiring in that plug. Just swap the engine wiring harness, that by the way runs inside the cab and has the computer connected. The only thing you may have to wire is the tranny computer if the pigtail isn't there already. It most likely is there.

I've got to run now, but I probably have the wiring schematics for both rigs in my archive if you need them.
 
old man pretty much nailed that.

the "frame" horns where the motor mounts bolt on have to be swapped, and you'll need to swap fuel pumps. the XJ stuff bolts on to the MJ sending unit with no troubles (pull 'em both out, put 'em side by side and you'll see how it works out)

only other issue is rear driveshaft (unless you have one from another 4.0L/aw4/4x4 MJ)

I REALLY pushed my way through the swap, and basically did it in the span of about 36-40 hours. the ONLY thing that isn't bolt-in is the rear driveshaft.

I wouldn't swap the dashes/wiring unless you absolutely have to. the XJ and MJ use two VERY DIFFERRENT body harnesses. but if you do go that route, the 6-pin connector under the driver's side kick panel is the important one (fuel pump, gas gauge, rear lights)
 
I really don't want to swap the dash and harness. I've heard that you might be able to swap the engine harness at the C101 connector. I haven't found any definite answer, but it's been mentioned here and on other boards.

Anyone have any insight on this?

Thanks,
Chris
 
you have to remove the c101 connector and replace it with the 4.0L version, they ARE different.

all it does is go down the firewall and into the back of the ECU
 
thread resurrection!

Okay I guess it's my turn. My 89 2.5L in my MJ has seen much better days. The body/frame of my 90 4.0L XJ has also seen much better days. So here I am. A good body/frame MJ and a good running gear from the XJ. The only real questions I have are electrical. The best I can tell, I need to use the XJ harness from the bulkhead to the engine bay, correct? This looks like a major pita, like removing ALL the wrap and seperating the wires from where they are wrapped into other wires (where they branch) and then rewrapping and routing. Is that the case or am I missing something? Will my XJ gauge cluster work in the MJ? I assume it just plugs right in. And lastly, the MJ has no a/c. Could the stock XJ a/c compressor make a good air compresssor? Just looking for a quick answer on that last one, I've done NO research on it yet. Thanks for your help NAXJA bretherin!
Dale
 
hey this is what im wanting to do with my 96 xj it has the 2.5 4cyl and i whant to put the 4.0 6 cyl in it it should be even easier for me shouldnt it.what problems will i run into mine is a manual trans
 
Re: thread resurrection!

roXJeepr said:
Okay I guess it's my turn. My 89 2.5L in my MJ has seen much better days. The body/frame of my 90 4.0L XJ has also seen much better days. So here I am. A good body/frame MJ and a good running gear from the XJ. The only real questions I have are electrical. The best I can tell, I need to use the XJ harness from the bulkhead to the engine bay, correct? This looks like a major pita, like removing ALL the wrap and seperating the wires from where they are wrapped into other wires (where they branch) and then rewrapping and routing. Is that the case or am I missing something? Will my XJ gauge cluster work in the MJ? I assume it just plugs right in. And lastly, the MJ has no a/c. Could the stock XJ a/c compressor make a good air compresssor? Just looking for a quick answer on that last one, I've done NO research on it yet. Thanks for your help NAXJA bretherin!
Dale

Hey Man.... I'm in K-town too!!

Right now, I'm looking at 2 88 MJ's.
1) 2WD 6 cyl 5spd (I would want to swap for the 4wd system on down the road)
2) 4WD 4 cyl 5spd (I would want to swap for a 6 cyl down the road)

Both about the same price, so I have been searching the forums about the swap thing myself if I bought the 4 cyl.

Have you done the swap yet? I'd like to check it out/help out, so I can learn to do it myself.


Thanks
Mike
www.jeepjeep.com
 
Re: thread resurrection!

JeepJeep said:
Hey Man.... I'm in K-town too!!

Right now, I'm looking at 2 88 MJ's.
1) 2WD 6 cyl 5spd (I would want to swap for the 4wd system on down the road)
2) 4WD 4 cyl 5spd (I would want to swap for a 6 cyl down the road)

Both about the same price, so I have been searching the forums about the swap thing myself if I bought the 4 cyl.

Have you done the swap yet? I'd like to check it out/help out, so I can learn to do it myself.


Thanks
Mike
www.jeepjeep.com

Cool! What do drive around here that I may have seen? I haven't done the swap yet. It may still be a little while. Personally, I would rather swap the running gear into a 2wd than swap the 6 into a 4 spot. But that's me, although I'll be doing BOTH :doh: Thanks for the link man, looks like it may have some good wiring info on it.
Dale
 
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