Swapping a 4.0/AW4 into a 4.2/tf999 YJ advice? - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 04-21-2017, 08:47 AM   #1 (permalink)
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Swapping a 4.0/AW4 into a 4.2/tf999 YJ advice?

Hi all,
I'm planning on taking the drivetrain from a 97-99 XJ (I would like Obd2 and distributor/ good head casting) and I was looking for some insight from someone who has done the swap. I'm planning on buying a whole XJ as a donor.

Firstly, some info on my current setup:
4.2/3-speed auto Weber, MSD, 4.0 head, etc.
It's still slow and rattly as hell, and needs more time, money, and tuning than I care to give it.
Ford 8.8 rear, 4.10s, 33x12.50s

I'm planning on moving the engine forward about 2-3" to give the driveshaft some extra room with the longer trans, since there already wasn't much room with the longer pinion of the 8.8. I have a new alum. rad and pusher e-fan, so there's tons of space in front of the engine.

My exhaust will bolt right up because I already have the 4.0 head and manifold.

I do have a couple things I'm unsure of though:

Column shift
I know that the MJ came with the same column as a YJ, but with the AW4, so will the stock shift linkage bolt up? I'm not worried about making one, but it would be nice if I could drop it in with minimal modding. Floor shift isn't an option because I have a 3rd seat up front.

Length
Is the overall length of a 4.0/AW4/231 going to fit with the stock slip yoke (temporary, going to SYE as soon as I can after the swap)? I've also considered using the drivetrain from a 4.0/auto YJ, but I'd really like the overdrive since this is my daily.

Fuel System
I'd like to keep the stock plastic tank and use an external inline pump to keep it simple, but I'm wondering if it might be better to get the tank from a 4.0 YJ and use that with the internal pump instead. The 4.0 tank may also work better with any emissions stuff I need to include.

Emissions
What will I need to make it run as clean as a 4.2 for a tailpipe test? I still have the YJ cannister and cat but I can plumb in the XJ one if necessary. It doesn't matter if it's throwing codes since my Jeep is old enough for a straight sniffer test. Would it be a more straightforward swap to use a pre-96 XJ?

Accessory Drive
Will the XJ front accessories clear the YJ Frame?

Thanks in advance for any input and I'll be sure to update the thread as I make progress.

Last edited by jcdj1996; 04-21-2017 at 08:55 AM.
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Old 04-23-2017, 09:36 AM   #2 (permalink)
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I'm in the middle of a similar swap but I used a 93 XJ motor and kept the tf999 ( I think I am regretting that already?! I'll be interested to watch your progress. I recommend getting your hands on a FSM, but since you have a donor you might not need it as much as I do. The battery tray will need to be rotated 90 deg. I got a new windshield fluid bottle from a 93 YJ so I could mount the ECU to the firewall. What's your plan for wiring? I got the engine, dash, and tub harness from a 91 YJ. It made more sense to spend the money than pinout and splice a bunch of wires. Getting your gages, speedo and tach to work will be a fun project. Hope you have some good pictures as lessons learned as you go. Enjoy your swap!

JoeP
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Old 04-24-2017, 01:53 PM   #3 (permalink)
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Quote:
Originally Posted by jp19 View Post
I'm in the middle of a similar swap but I used a 93 XJ motor and kept the tf999 ( I think I am regretting that already?! I'll be interested to watch your progress. I recommend getting your hands on a FSM, but since you have a donor you might not need it as much as I do. The battery tray will need to be rotated 90 deg.
Why did you need to rotate the tray?

Quote:
Originally Posted by jp19 View Post
I got a new windshield fluid bottle from a 93 YJ so I could mount the ECU to the firewall. What's your plan for wiring? I got the engine, dash, and tub harness from a 91 YJ. It made more sense to spend the money than pinout and splice a bunch of wires. Getting your gages, speedo and tach to work will be a fun project.
Gauges will use a 92+ Speedo/Tach cluster, but the early style center gauges. I couldn't bear to part with the analog clock! I'll probably just find places for the old sensors in the new engine, since I've already whittled down my old wiring harness to just control lights and gauges. I'm planning on thinning out the new harness in the same manner, to only control the engine and trans (plus speedo and tach).

Quote:
Originally Posted by jp19 View Post
Hope you have some good pictures as lessons learned as you go. Enjoy your swap!
JoeP
Thanks!
__________________
"Douglas" the 89YJ, typical mods: Weber,MSD,8.8 w/GT disc brakes
Canadian daily driver, project car

Last edited by jcdj1996; 04-24-2017 at 01:54 PM.
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