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1997 TJ 2.5L to 2003 4.0L Swap

1220 Views 13 Replies 3 Participants Last post by  jeepshak
Hi Folks, been searching for a while and digging through the FSM's and keep getting conflicting information.

Back story: Currently have a 2.5L 5spd in my 1997 TJ... I was able to get a 4.0L engine/trans/t-case, wiring harness (body & engine), charcoal cannister, cpu from a 2003 donor. My research so far indicates that the 2003 fuel tank/system is a bit different as it has some additional components i.e flow control valve (#9 in the attached picture below) and a bunch of vapor hoses with connectors that interface with it. I live in CA and would need this to pass smog. Also, I understand the trouble involved with this swap is similar to swapping in a v8 etc. , at this point...(dare I say?) it is, what it is. So let's move past that.:smile2:

I understand that if I just purchase a fuel tank and the flow control valve setup from a similar year, I'll be good to go (I think)... Where I need some input (from you fine folks) on is coming up with a workaround to keeping my current fuel tank. I think the very least I would have to: 1.) make a harness adapter for the fuel pump module connector (from 03 wiring harness to 97 fuel pump module) 2.) purchase the flow control valve assembly with it's hoses. I haven't been able to find a schematic of fuel/vapor line system. I'm hoping someone out there has done something similar or can point me in the right direction. Thanks in advance.

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Discussion Starter · #4 ·
I have the complete wiring harness (dash & engine), computer, airbag module... My concern up until seeing your reply was with the fuel and evap system... is there more that I'm missing? BTW thank you for the taking the time to respond. I appreciate it.
 

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I have the complete wiring harness (dash & engine), computer, airbag module... My concern up until seeing your reply was with the fuel and evap system... is there more that I'm missing? BTW thank you for the taking the time to respond. I appreciate it.
I honestly don't know how much of the wiring harness you'll need to change but people who swap a Hemi into their older TJ's make it work.

I'd look at some of the swap threads for swapping a Hemi as it will have more of the information you need.

I have a Dodge magnum V-8 in my TJ so I know about the fun of engine swaps.
 

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Be sure to check with the state on what exactly is required to get smog certification to get it registered. It may be more complicated than expected.

Without getting into any of the mods to the frame (engine mounts) & other things involved in the actual swapping the 4.0L into the 2.5L vehicle since that info is widely covered in these forums I will only add to what wildman4x4 said.

You are going to have a lot more compatibility issues than the EVAP system. You are going (more or less) 2 generations from '97 to '03 is several areas. There will be a number of wiring issues starting with the '97 is CCD Bus & the '03 is PCI Bus. You will probably have to source a cluster from a '03 or maybe a '04. That will be needed to get gauges to work with the '03 PCM. Other things will likely not match up when trying to plug the '03 harnesses into things already in the '97, both under the hood & in the cab. The HVAC is completely different. The headlight switch is relocated to the multifunction switch. So it is wired differently. Fuse blocks have fuses assigned differently. Probably other issues too.

Wiring wise you should definitely go with harnesses no later than 2000 for reasonable compatibility with '97s. Changes in '01 & '03 really complicate things.

If you go forward you will need both year's FSMs & a very good understanding of electrical wiring for sure.
 

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Discussion Starter · #7 ·
Thanks for the feedback, friends. I'm good with the mechanical stuff (already have motor mount relocation brackets, ax-15 transmission, t-case, drive shafts etc.) , it's the electrical and the fuel system that's got me worried. I think I'm slowly accepting the idea that it's probably best to sell the 2003 motor and find one out of a 97/98.
 

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That will save you a HUGE headache. You then only need the engine harness.

You could even go to '99-'00. If you do, there is one slight modification to the '99-'00 harness & it will plug right into the '97 under dash harness. I have been helping this guy with a similar job (in reverse, '00 tub, '97 engine).

https://www.wranglerforum.com/threads/tub-swap.2421578/#post-35005741

Everything including the harness mod is in posts 12 & 14. For '97 tub, '99-'00 the engine harness gets the wiring splice on the other side of the connector (same wires).


Any issues with the state/smog cert.?
 

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The thing not mentioned yet is what is your build date? It seems the 01-03/96 TJ's had some wiring that is different than what the wiring diagrams show.
Of course my TJ is a 01/96 build date so I fall into that group.

I agree that finding a 97-99 TJ would make life the easiest to do if you're dead set on the 4.0.

I'm going to ask, Why not swap to a V-8 if you are already going thru all this trouble? Just asking.
 

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Discussion Starter · #10 ·
You made me go check my mfg date... 7-96 ! lol . As far as why not just swap to a V-8? ... At this point, swapping to a 97/98 4.0 I only need the engine, wiring harness and the PCM. I already have an AX-15 and transfer case, drive shafts, and M.O.R.E motor mount relocation brackets... Everything else (i.e. fuel system, dash wiring and all the other bs that I was initially facing) stays the same. If I were to swap to a V8, I believe I'd need additional adapters, bellhousings, wiring harness, some funky fuel line system that I know nothing about at this point... I've also read that I'll need to swap out my dana35's (which I'll probably end up doing somewhere down the road). This entire endeavor started because I need to rebuild the 4banger, and since it's my daily driver I decided to upgrade while at it so I'm not competing for a spot with the big rigs on any slight incline on the fwy... fun stuff. :smile2:
 
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I'm not knocking you for wanting to do the 4.0 swap over a V-8 swap it's just that for almost the same amount of work you can do the V-8 swap.

To do the V-8 swap you'd need a Dakota bellhousing if you want to keep the AX15. Then you need to blend the wiring harness from the V-8 and the Jeep. It isn't hard but takes a little work. If you wanted to do the V-8 swap one way would be to get a wiring harness from a 97 TJ and get the blending of the two done a head of time. Then AA motor mounts welded in place and you are there.
Will your D35 live behind a V-8? Sure if you don't have a heavy foot.

Yep I was a little shocked when I looked at the build date on mine and wasn't real happy with I found out it was a 91/96 build.

If you want to know more about the V-8 swap here ya go:

https://www.jeepforum.com/forum/f9/wrangler-magnum-v8-discussion-1365878/
 

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Discussion Starter · #12 ·
thanks for the feedback Wildman, I just glanced over the thread you sent... looks like a lot of great info that I'll go back to look through... I posted this in another thread (https://www.jeepforum.com/forum/f9/downgrade-2006-4-0-engine-work-1997-tj-4431533/) ... but basically, why wouldn't I be able to use a 2006 motor in a 97 setup (with 97 wiring harness & pcm) if I "downgrade" from the coil packs to a distributor system ... and possibly address a few electrical connectors/pinouts based off of information from the FSM... As well as replace the exhaust manifold / cat system with a 97 type setup. I figure the engine itself is basically the same 4.0 engine, it's just the fancy ignition system that changed. I'd leave the rest of the accessories (starter, alternator, etc.) alone and just change the pinouts if needed. Could it really this simple? Thoughts?
 

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thanks for the feedback Wildman, I just glanced over the thread you sent... looks like a lot of great info that I'll go back to look through... I posted this in another thread (https://www.jeepforum.com/forum/f9/downgrade-2006-4-0-engine-work-1997-tj-4431533/) ... but basically, why wouldn't I be able to use a 2006 motor in a 97 setup (with 97 wiring harness & pcm) if I "downgrade" from the coil packs to a distributor system ... and possibly address a few electrical connectors/pinouts based off of information from the FSM... As well as replace the exhaust manifold / cat system with a 97 type setup. I figure the engine itself is basically the same 4.0 engine, it's just the fancy ignition system that changed. I'd leave the rest of the accessories (starter, alternator, etc.) alone and just change the pinouts if needed. Could it really this simple? Thoughts?
I honestly do not know and have only looked at the newer engines but never really had to work on one. So hopefully someone with more experiance will reply and let you know. I thought I'd read somewhere that the newer blocks didn't have a spot for the distributor. But I could be confusing things too.

That V-8 thread is long but a lot of great information. Good luck.
 

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Discussion Starter · #14 ·
just FYI and for anyone else interested... I was able to pop in a 97 distributor in the 06 engine. I think this is going to work... Will document and share my process on JF. Thanks again for your feedback.
 
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