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Discussion Starter · #1 ·
First post and not familiar with the forum. I've had my 89 2.5 for 10 years and it failed emissions. I did pick up a 97 4.0 with a manual tranny the runs strong and is sitting there. The entire drive train on the 97 seems good, but the frame is a total loss due to rust. Is there a thread on a TJ drivetrain swap into a YJ? I'm thinking the motor, trans and transfer case, computer and harness, but what other stuff? Is the dash integral (speedometer)?
I've got the time and space, so am looking for a link to someone that has done this and took the time to post the swap. If I do it, I'll post how it goes.
Thanks for any suggestions and lnks.
 

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First thing to do is check with your state regulations to see what engine swaps may be legal.

Consider:

1) Converting the 4.0L from OBD2 to OBD1 (involves replacing sensors and injectors)
2) Use a 91-95 4.0L ECU and 4.0L wiring harness
3) Convert your dash over to a 91-95 (wire harness, gauges, etc)
4) Figure out your fuel delivery options (Is 89 compatible? If not, upgrade to 91-95)

I've got a 97 TJ 4.0 in my 95 YJ, which was originally a 2.5L. So my swap was a little easier. I was able to reuse my wire harness with minor mods.

In your situation, I'd probably rather do a Chevy LS swap than deal with the 4.0L swap.
 

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Maybe open the box a little further.... maybe swap the whole tj onto the yj frame

Leaf spring tj
 

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Since you have a complete 4.0 OBD 2 system use it all

The fuel pump
The exhaust and sensors
The wiring harness
The cluster



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Agree with Digger. I'm pretty sure that OBDII Jeeps run on 45 psi. Your 89 (if TBI fuel injected) runs on 15 psi.

If you just take the ENTIRE system and swap it over, you'll just have to figure out the fabrication for fitting it in a new chassis. Motor mounts, etc. I believe the transmission crossmember is set up for both engines and transmissions... Not 100%.

The main issue would be the dash wiring.
 

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What you are considering is impossible to do! PM me with your address and number and I will come by and take both Jeeps off your hands. I don't have much money but I'm a nice guy.

But seriously now folks, I would follow Digger84s and Mud Magnets advice and use the whole shebang.
Installing the TJ tub on a YJ frame can be done, but you have to change several body mounts on the tub.
You probably already know that you have to move the 4cyl. motor supports to where they will support a 6cyl. engine. Requires a welder.

You can probably use the TJ dual diaphragm brake booster in place of the original YJ single diaphragm booster. I have a DD booster from a '97 TJ and it looks like it will fit with only slight modifications to the brake lines. It looks like there won't be any modification necessary to the brake actuating rod, though that's by visual inspection only and I haven't measured it yet.

As far as the dash wiring, you will need schematics from a '89 YJ and a '97 TJ. I would use the entire TJ underhood harness and make the adaption within the firewall plug.
For instance, the tach wire for TJ may be in a different location within the plug than the tach wire for the YJ is. Simply move the TJ wireing harness tach wire where it will meet up with the YJ tach wire on the cabin side of the plug.

Examine the plug very carefully. There is a locking slider that holds the metal connectors in the plug. If you don't pull the locking slider (I seem to remember that it's red or orange plastic) you won't be able to remove the connectors so that you can move them around to where TJ tach wire (underhood wire harness) can meet up with YJ tach wire (cabin wire harness).

Not saying that you will find that the tach wires don't already meet up...just using the tach wire as an example. In the electrical schematics there is a chart that shows each wires location within the plug. I fully expect that the TJ and YJ plugs will easily fit one another, just that the location of some wires may be different between TJ and YJ and the TJ plug may have additional wires that you won't find on the YJ (maybe power for anti-lock brakes or air bags). You will probably want to add the OBD2 plug wires to the YJ plug. There may be a couple other wires that I am not thinking of right now.

There may be some dash things that you will need from the TJ like the OBD2 plug. For simplicitys sake I would keep the majority of the YJ underdash harness and simply add the necessary tidbits from the TJ dash harness.

Will the TJ fuel pump fit into the opening of the YJ fuel tank? Will the entire TJ fuel tank fit in the YJ? (I don't think so).

This is an interesting project. Please keep us updated. Pics would be nice.
Where in Colorado are you located?

Good Luck, L.M.
 

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Pretty good till you got to the cluster
All the tj gauge info including tach is encoded info from pcm sent to cluster on a communications bus

On 97-2000 TJ that bus is a twisted pair of wires called the CCD bus

On 2001-2006 TJ it is a single wire PCI bus

On 97-2001 XJ it is a twisted pair CCD bus

Not sure about 96 XJ but pre 96 XJ and all YJ don't encode cluster info on a bus





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OP has some work cut out for him when it comes to dash wiring.
I kinda/sorta remember seeing a YJ with an XJ harness. The computer was installed on the passenger side fender apron. I don't know if that was a factory location or if the owner of the YJ that I saw did some creative engineering.

OPs donor vehicle is a '97 TJ. Does the TJ PCM mount on top of the heater box like a YJ or does it mount elsewhere.
Oil pressure, and water temp should be no issue. Simply use the YJ sending units.
Fuel shouldn't be an issue either.
Tach, speedo and ammeter could require some creativity. I don't think the swap has any insurmountable obstacles. Will the TJ tach & speedo mount in the YJ dash? I don't recall exactly what a TJ cluster looks like.

Pics???

Good Luck, L.M.
 
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I don't like the post 95 4.0's seems like they all had problems cracking piston skirts and heads. I read somewhere the Renix blocks were the strongest because they had a higher nickle content. But i have owned a lot of 91-95 HO's and never had a problem with any of them. I have had problems with post 95 4.0's though so i swore them off. Chrysler lightened the rotating assemble in 1996ish to get better fuel efficiency and ruined the durability of the 4.0, the newer style intake manifold was nice though.
 

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Discussion Starter · #10 ·
thanks

Thanks for the feedback. I spent almost 6 hours scraping the interior of all the gross leftovers of the previous owner from the interior of the 97. I'm going to repair the frame so that it's a running vehicle and make sure all the mechanicals are worth the work to do a swap. Both might be sufficient to play with for the summer and if I want to get serious about this, it sounds like I'll have a hell of a project to work on.
 

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Look at the practicality!

If you get both Jeeps operable, perhaps you can sell them both and buy a 1994-1995 YJ with a 6cyl. engine and save all the brain damage.

Good Luck, L.M.
 

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Sell the 87 and buy good used frame for the 97!
 
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