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Replacing XJ 4.0 with new TJ 4.0

3XJFamily

NAXJA Forum User
Location
Austin TX
I am looking at replacing my very tired 91 4.0 HO with a 2005 TJ 4.0 (complete engine airbox to cats with all accessories, serpentine belt in place). . .

Looks like using my intake and existing ODDI system is the best bet (just don't want to deal with changing to the new computer). What about injectors?. Mine has 19.5 lb, I think these may be 22.5 and incompatible with my wiring harness. Any idea what I can use from the '05 intake?

Exhaust from the '05 is much improved split with dual cats - any idea if it will fit with minimal fabrication, or just go with a header?

I'm asking for 2 reasons: 1) Still negotiating a price on the engine, and omitting intake/exhaust and engine computer is an option. 2) I am having a shop do the swap so will have to consider labor and parts.
 
that's gonna take a TON of modification.

the ENTIRE FRONT of the block is different.

NONE of your accessories or brackets will bolt on

you'll have to figure something to replace the mechanical fan because it's IMPOSSIBLE to put the XJ mechanical fan on that motor.

to top it off, you're left with spending all that money and effort to install a weaker 4.0L w/ a junk head.

new does not mean improved.

go buy a junkyard 4.0 (91,92,93 or 95) and drop that in.
 
It is going to be nitemare, none of the connectors will mate up, different pulley system and thats just off hand stuff I can think of, the TJ has a centered mech fan the XJ does not. You'd be better served buying a Jasper long block which will have EVERYTHING but brackets and accys installed. Even if you are getting this for free it's not going to be a quick job. This will be, at a minumum, on par with going from a 2.5 to a 4.0.
I have looked at 04 and 05 TJ's and was suprised at the differences, good differences but differences just the same, like the alt up top now out of the water and mud. We have two 97TJ's and we just rebuilt one that was rolled so I know the differences between a 97TJ and a 98XJ and even on those there are some doozies...
If you do this TAKE PICS and DOCUMENT this for future use including your mistakes....
 
OK, wait a minute -

This '05 TJ engine has EVERYTHING, it is a takeout and comes with ALL accessories in place and the serpentine belt still on! Engine harness comes with it!

Am I missing something? It sounds like the immediate issues identified are resolved by replacing the mechanical fan with an electrical fan, and splicing in some new connectors from the harness that comes with the new engine?

A Jasper engine is running $4000 - $5000 installed here. I'm looking at about half that - installed. I have a very good installer with his own shop and 20+ years experience working exclusively on Jeeps (maintenance to rock crawler builds).

PLEASE give me some more specific details. Does someone knows If the 91HO intake will interfere with the accessory brackets for the '05? Does the TJ exhaust follow the same basic path as the XJ? Someone have both these in the driveway and can look? I'm not discounting the earlier advice, just want more. . .
 
Couple of more things that come to mind, the alt and a/c compressor are reversed, will the compressor clear down there on the XJ, which means different A/C hoses if yours can't be routed down there. You *might* be able to treat it as a long block and move all your brackets and stuff over to the new one as well as the intake, TB and take advantage of the situation and up grade to a good performance header. I'm not saying it can't be done, if your mechanic says he can do it just make sure he's not billing you for time, get a firm commitment on the cost for labor from him and hold em to it. As far as fabbing up brackets and moving stuff thats different and you'll probably eat it on that end a bit.
Also, the TJ is what, auto or stick ? Is yours a stick or auto, might be talking flywheel here, not sure. It's not un-dooable, not if they can put a V10 viper in a TJ it isn't....
As for a jasper being 4-5K, wow, thats steep, had one done in our oldsmobile cutlass two years ago, V6, $3200 installed and out the door w/new radiator. I priced one at my friends shop just for fun and a 4.0 for my 98 was $2200 delivered, that was about 2 weeks ago and jasper is alot closer to you than to me here in Pa. Whoever quoted you that must be wanting a new boat or harley...
 
3XJFamily said:
This '05 TJ engine has EVERYTHING, it is a takeout and comes with ALL accessories in place and the serpentine belt still on! Engine harness comes with it!

Fair enough. The above points notwithstanding, how do you intend to make that harness work with the existing (entirely incompatible) computer? Even if you change the computers out, you're still stuck with having to replace the instruments (and that's just the tip of the fiddly electrics iceberg).

I can't give you more specific advice as this is not something I've ever even seen attempted, but there are some major differences between '91 and '05 engines and how they're controlled. Not trying to discourage you, but the little stuff may well nickel and dime your cheap replacement engine project to death.
 
The "plan" was to use the 91 intake and existing OBD1 in the XJ, and splice in connectors from the harness on the '05 for accessories to avoid the electronics issue.

I went and looked at an '05 and see what you mean about the AC pump hanging low and being reversed - this one comes with the long TJ hoses but, there's a good chance the AC would be right up against the steering box in the XJ.

Stripping it down to a long block kind of defeats the purpose as it adds labor, and I lose all the new accessories.

Thanks for the additional thoughts, I'm convinced at this point that even with everything on it, it's not worth the effort to just accomplishing replacing a 4.0 with a 4.0
 
Using the 05 computer and wiring harness and mate it to the 91 XJ with be easier. I finished installing an 03 4.0L TJ engine/tranny/xfer case (with 20 miles to factory new) into my 95 YJ. You will know the wiring inside and out when your done.

Your 91 ECU doesn't work with two precat O2s. MAP signal is different, uses 3 coils instead of one. You will need to have custom A/C lines to keep the A/C. Your NEW engine requires 50 PSI of fuel pressure. The 05 fuel rail does not have a fuel regulator with a return line (05 TJ has intank reg). This is just to name a few. Lots of little issues to work out and to think about. Message me if you need any info about my swap...
 
New plan . . . STROKER!
 
Also the exaust is routed different than our XJ's - It wraps around the front of the oil pan.. A stroker sounds like a much better option...

Will.
 
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