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Transplant Question


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I am planning to transplant the drive train fron a 1991 XJ 4.0 auto 4x4 into my 1990 MJ 2.5 stick 2x4. How much wiring will need to be changed? What about the fuel pump? Instrument cluster? What about the rear diff,don't wana go soa? I don't need the ground clearance just the 4.0 and the traction for boat ramps. I just bought this XJ and the wife will be driving it till I get her EXploder repaired. Then maybe later I will get her a nicer newer XJ. :D

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You need to move EVERYTHING.

 

Is your MJ a 4 speed or a 5 speed?

 

And with you referring to SOA, a XJ axle will not bolt directly onto an MJ as SOA. The distance between the perches is also different between XJs and MJs.

 

If your MJ is a 4 speed, chances are pretty good it's got 3.55 gearing, which is what the XJ should have. You will need to get your rear driveshaft cut down.

 

But for the wiring, you need to move everything in the engine bay and dash. Basically strip the MJ to bare bones, and move everything over from the XJ.

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:agree: The entire engine/dash wiring harness, ECU, and TCM needs to go in the MJ. You can keep your OEM fuel pump but if you do not pull the pump and rewire the sending unit potentiometer (easy to do), the gauge will read backwards. :D

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He'll need to change the pump. He's going from 1 injector to 6.

 

One injector in a 1990 2.5L EFI? Don't think so...........

 

The replacement Walbro pumps from NAPA are the same for the 2.5 and 4.0 engines; however the OEM-type Bosch pumps (recommended) carry different p/n's for the two engines, N69301 vs. N69302.

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He'll need to change the pump. He's going from 1 injector to 6.

 

One injector in a 1990 2.5L EFI? Don't think so...........

The 1990 4-cylinder was still a Renix-based throttle body system with one injector. The 2.5L was updated to the multi-port Chrysler system in 1991, the same year the 4.0L was changed over to the Chrysler system.

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He'll need to change the pump. He's going from 1 injector to 6.

 

One injector in a 1990 2.5L EFI? Don't think so...........

The 1990 4-cylinder was still a Renix-based throttle body system with one injector. The 2.5L was updated to the multi-port Chrysler system in 1991, the same year the 4.0L was changed over to the Chrysler system.

 

Crap - I did not know that Eagle, thought the MPI was incorporated earlier on the 2.5L's. My apologies Geonovast. :bowdown: So what about the 2.5L fuel pump? Think it might work w. the 91 HO 4.0L after seeing the NAPA 1990 results? Guess I could cross the two Bosch pumps and check their output pressures and GPM specs.

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My Mj is a 2.5 5 speed the donor is a 1991 4.0 sefi auto 4x4. I am looking forward to the 6 cyl power and the auto tranny. I really don't need or want the 4:10 gears I have now so I will probably install the xj rear and weld new perches in the proper position. The fuel pump is another matter can I remove the MJ pump and replace with an XJ pump? I plan on retaining the MJ cluster so sending unit rewiring won't be a problem. Does the 91 tranny have a cable driven spedo? Man I wish I had this donor when I was building this truck a few months ago. :doh: Now I have to remove the dash again. :fs1:

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You cannot retain the MJ cluster. ALL the dash wiring will need to be moved over from the 91 donor, so you have to use the 91 cluster. I'm assuming you want to keep the 90 cluster because it's a full cluster? You'll need to find a 91-96 Full cluster in order to keep that.

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The XJ has a full cluster also and the cluster it self isnt an issue but I want to keep the MJ spedo if possable cause it has 100k less miles on it and the gages from the clusters don't match.If I have too I will. Can I just get a new 91 fuel pump and install it on the 90 tank unit?

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The XJ has a full cluster also and the cluster it self isnt an issue but I want to keep the MJ spedo if possable cause it has 100k less miles on it and the gages from the clusters don't match.If I have too I will.

http://www.naxja.org/forum/showthread.php?t=921205 Shows you how to change the new cluster to reflect the old cluster's mileage reading.

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