Join Date: Sep 1999
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Re: Swapping from a XJ to a CJ-7 (need advise ASAP)
I have done this exact swap (91 XJ 4.0 into 83 CJ-7) so here are some things to think about.
I ended up using the mopar kit wiring harness, computer, and some various other items, air filter kit, throttle cable, and distributor( a 95 item, different from the 91).
I had to buy a flywheel from mopar, as I had already swapped in a t-18 and I was keeping it.
I also bought a different harmonic balancer, to use a front mounted crankshaft positioning sensor, much better than trying to adapt one onto the bellhousing.
The water pump has to be changed out for a YJ piece so you can bolt a fan to it (look at the motor and you will see what I am talking about.
The 258 motor mounts bolt right onto the 4.0 block, except for tapping out one hole, the boss is in the block just needs tapped, had to a buy a metric tap just for it.
I kept the delco alternator and had to do some fab work on the alt mounts, it's been so long I can't remember exactly what i did but it works!
My 258 was a CA model and had a serpentine belt, so swapping some items was possible. For instance the ac pump on my 4.0 was trashed, so i pulled it off. i needed a pulley there though for the serpentine belt. I was able to use the ac delete/idle pulley off my 83 258 with only slight modifications. Also the fan off my 258 was reverse rotation so I was able to use it. I know a guy who did the same swap but used a regular rotation fan and couldn't figure out why it was overheating.
i used the pump out of the xj tank mounted on the frame. As i remember it had some strange inlet/outlet sizes that required much work to make work. The mopar kit pump has "normal" size inlet/outlets that is much easier to make work.
I used the existing fuel lines, but mounted the xj filter in the engine compartment on the pass fender, then the line passes underneath the motor to the driver side where it goes into the fuel rail. Used the existing fuel return line, just cut it and ran rubber line to it. Be sure to use rubber line rated for HI PRESSURE FUEL INJECTION, and inspect them periodically.
BIG NOTE; I installed a low pressure fuel filter between the tank and the pump for insurance. About 6 months after the swap I experienced a hi speed bucking/lack of power, like it wasn't getting gas. turns out this filter was completely clogged with bright silver metal chips. I can only figure that when I was cutting the various fule lines that some of the chips got into the system and circulated through unti being caught by the filter. "USE ONE"
Very happy with the swap. Plenty of power, very smooth, starts quickly, extremely hard to make it stall. top end much better than the 258 and while you can tell there is a little less low end torque, the smoothness and the fact it can't be stalled more than makes up for it. No more stumbling/stalling/hard starts on steep uphills. And as a matter of fact the bbd on the 258 actually ran really well, i had no complaints, just came across the motor for a really good deal. If I ever get another Cj with the 258, this would be a standard mod.
ps i have heard of 258/mpi kits running a little lean. To me swapping in the whole motor made more sense. It runs perfect. I have a digital camera so if you need pics let me know, any questions just ask.