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2.5 Renix to 4.0HO Swap


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I have a 1989 Jeep Comanche with the 2.5 I4. I also have a parts 1994 Cherokee for parts which has a 4.0HO. What is involved with the switch from renix to HO? I know I'd need to swap computers, but what else? Also what will need to be done in order for me to pass CT Emissions with a different motor in the vehicle?

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Call the emissions station you use and ask what rules will apply. In some states, your vehicle is tested according to the year on the VIN even if you swap in a newer engine. In other states, if you swap in a newer motor you have to meet the emissions for that year.

 

Plus you're going from a 4-cylinder to a 6-cylinder.

 

My guess would be that a 1994 4.0L will pass the emissions for an '89 4-banger with no problems, so maybe you don't have to say anything. I don't think they open the hood -- I believe they just verify the VIN, stick the sniffer in the tailpipe, and run it up on the dyno. Oh, and the gas cap pressure test.

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The frame horns on XJ/MJ's are bolted on (not like TJ's that are welded). You'll need a set of 4.0 horns, the bolt holes/studs are there already so you can just bolt them in. 2.5 engine mounts look very similar to 4.0 ones but won't work...you'll need 4.0 ones.

 

Couple other things that are different, aside from all the wiring:

 

-throttle cable

-radiator (remove the 2.5 radiator shroud brackets and the 4.0 one drops in)

-coolant overflow bottle of some kind for open system (I reused the 2.5 one but had to modify the wiring harness on the driverside fenderwell and eliminate the EGR solenoid)

-cover plate on transmission tunnel above shifter

-fuel lines, you'll have to splice the 2.5 ones into the 4.0 fuel rail (I used rubber fuel line, some barbed fittings and clamps)

-fuel pump (you need a 4.0 one, runs at a higher psi)

 

 

Have fun :D

 

Jeff

 

edit: disregard the coolant overflow bottle.....you can use the stock HO one out of your XJ. I couldn't use the HO setup on my renix swap because of the way the overflow mounts by the coil area, that's why I reused the 2.5 one.

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So for my complete motor swap I will need the following off my parts Cherokee. Correct me if I am wrong.

-Motor

-Computer

-Wiring Harness

-4.0 Horns

-4.0 Motor Mounts

-Throttle Cable

-Radiator

-Coolant Over Flow Bottle

-Cover Plate on Transmission Tunnel above Shifter

-Fuel Lines

-Fuel Pump

 

Am I missing anything?

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by wiring harness, we mean the COMPLETE harness both underhood and interior. Since you're using an XJ donor you'll also have to splice in the MJ sub-harness in the cab that feeds the rear lighting circuit and fuel pump (MJ is slightly different than XJ in rear lighting circuitry). Your list is pretty much complete, though. I'd suggest you strip the MJ engine bay bare first, then swap the XJ harnesses in and start transferring everything from under the XJ hood into the MJ.

 

Jeff

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You don't mention what transmissions you're dealing with, you'll need the 4.0 trans as well. This will also require the driveshafts be changed. The front one from the XJ will work but you'll need to find one for the rear or have your current one modified. As for the fuel pump, the entire XJ sender will not fit the MJ tank but I think you should be able to swap just the pump.

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i doing the same swap and your going to need just about everything from the cherokee, when we were done with the cherokee it was just a tub and now i just having trouble with the tail lights wiring up the xj to the mj tail lights but it was an easy swap for most of it.

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  • 4 weeks later...

engine trans transfercase engine wiring engine bay accessories radiator (you already have a 4.0 rad support so long as the MJ is 87+) computer(s) fuel lines fuel pump (sending unit needs changed) all dash accessories, heater box if you want the a/c to work/if you have it, dash wiring shifters. then you need to add in a brake light wire on the dash harness and splice everything for the rear lights and fuel pump.

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