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Discussion Starter · #1 ·
My friend, Kenny,has a 90 YJ with the 258 and is wanting to convert it to F.I.
Can you get the fuel incection off of a 4.0 and convert it to the 258?
He has found a wrecked 4.0 (MJ I think) and all the stuff is there, the guy said he could have everything he needs for the conversion off the donor vehicle for around $300.00, so if it is a possible conversion is it worth going for?
Thanks
Cory

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If it is 91+ then it is worth it. It will also need the head off the 4.0, as the intake will not bolt up to the 4.2 head. The 4.0 head is far superior in flow anyways. This also means you need the exhaust manifold for the 4.0. Then there is the intake manifold, fuel injection rail, throttle body, map sensor(off the firewall), cps(probably on the bellhousing(this has some options)), and perhaps the VSS off of the tail of the tcase. Of course you will need the computer and the wiring harness for it all to work. It is a viable option to take the whole drivetrain from the donor. The 4.0 is a great motor and could be rebuilt and bolted into the YJ with the MJ tranny and tcase???

My experience leads me to this choice. The 4.2 bottom end makes great torque, but the 4.0 is almost the same.

I put the MOPAR kit into my 90YJ and I am happy with it, but the $$$ was outrageous.
edit : I guess my website is down
 

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Discussion Starter · #3 ·
we'd like to just swap the whole 4.0 in but his 4.2 was just rebuilt about 10,000 miles ago. He's checking on getting the head and system off of a 98 grand cherokee that he also found and it only had 61,000 on it but only the top end is good.

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That works, just determine where the CPS is located, and if it is in the bellhousing, it will have to transfer to the YJ. Mine came with a CPS that attached to the front of the motor and uses a new serpentine belt pulley. The 98 stuff kicks ass. Same head, but tuned for almost 20 years. The intake manifold is AWESOME! Good for 25hp I have heard. When adapting the head to the motor, it is likely that you will not have to fill the water jackets on the head. That year block is known to have a wide enough deck to get rid of the clearance issues. Simply, if the block is the same width as the head that you are putting on, then you wont have to do anything to the head.
 
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