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Unread 01-06-2014, 02:16 PM   #1
guitarpro66
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1988 MJ Comanche 
 
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Location: malaga, new jersey
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will 91 FI motor work in 88 body

I have an 88 mj im gonna be doing a bunch of work to soon (axle swap, 5 speed swap, 8in lift, ect.) I have a donor 91 xj and I was wondering if the motor is a direct plug n play of do I need the harness from the 91. both are fuel injected

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Unread 01-06-2014, 05:00 PM   #2
Soldier905
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Everything should easily swap over but swap everything from the XJ over the the MJ (engine ,engine harness and such). The Comanches and Cherokees are the same vehicle from the front doors forward . Being a 88 you may have a renix system in it so i don't think the wiring harness would be compatible with the newer obd 1 system of the 91 (iirc 90/91 is the start out years for the obd systems)
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Unread 01-06-2014, 07:50 PM   #3
cruiser54
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Here's the real answer from someone who has done it 3 times:

Cruiser’s HO into Renix Swap

This swap is easier than some will lead you to believe, generally those who have never done it. Those of us who have done it, like myself, will share with you the things that need to be done for a successful swap. Just think of it as swapping in a long block.

The HO and Renix have some differences but none that can’t be overcome very easily.

Any HO engine from an XJ or ZJ through 1999 can be used. One running change was that the rear of the head was no longer drilled and tapped for the temperature gauge sender beginning in the 96 model year. The sender can be relocated to the threaded hole in the thermostat housing taken from the HO engine. You’ll have to extend the wire to that location. Some brave souls even drill and tap the HO head for the sender.

You will be using the intake and exhaust manifolds from your Renix, along with all your sensors and wiring. Since the intake ports of the HO are slightly different, you use the Renix gasket. Exhaust ports are identical.
You will need to use your Renix distributor as it is different than the HO because they use different fuel management systems. The flywheel or flexplate from the Renix must be used so your CPS gets the correct signals. The valve cover from the Renix allows you to keep your CCV system intact and requires no modifications.

The HO block will have a plug in the coolant galley on the driver’s side of the block, closest to the front, which needs to be removed so your Coolant Temp Sensor can be installed in it’s place just as it is on the Renix. It requires a 5/16” square drive or a modified 3/8” drive that has been ground down to fit. Do this before installing the engine.

As for the knock sensor, which is located just above the oil pan on the driver’s side of the engine about mid way, all the blocks I’ve seen are threaded for it. If not, I’ve heard they may be drilled but not tapped. Tap the hole if that’s the case.


Revised 03/28/13
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Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
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Unread 01-06-2014, 11:16 PM   #4
guitarpro66
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Thanks guys for the info. I just wanted to make sure before I start doing all this work. The write up answered all my questions. Thanks again
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Unread 01-10-2014, 05:35 AM   #5
cruiser54
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Quote:
Originally Posted by guitarpro66 View Post
Thanks guys for the info. I just wanted to make sure before I start doing all this work. The write up answered all my questions. Thanks again
Any ? along the way, post them up.
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Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
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Unread 01-10-2014, 05:47 AM   #6
dkroll
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Let me know how your 8 inch lift goes, mine is still in progress.
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Unread 03-30-2014, 07:21 PM   #7
champdmb
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This forum is amazing! I have had only two issues regarding owning Jeeps and they ahve both been solved within minutes of logging in here! I only hope one day I can repay with some help of my own to someone else! Cruiser... your post nailed all of my concerns about my newest addition to the family... a rust free 89 manche that will be getting a 98 4.0 from an xj put in her in the next couple of days and you just confirmed a lot of my fears while at the same time solving them! Great info! I will post some pics and update as I go.

Pretty sure I am going to do a restore on this one as asside from the engine the only additional need is fresh paint. May not be able to resist turning it inot another toy though.
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Unread 04-01-2014, 12:50 PM   #8
ewingtkepa
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Cruiser54 is correct.
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