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Old 04-02-2012, 11:48 AM   #1
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2.5 to a 4.0 ??

What all do you have to swap out need help or tips ?

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Old 04-02-2012, 11:55 AM   #2
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Old 04-03-2012, 10:06 PM   #3
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I was thinking of doing same thing, I am a mechanic so thought I had some advantages. All I hear from peeps is its not worth it, go buy a YJ w/ the 4.0L. Thought I would buy a cherokee doner that way I have anything I would need. brackets, harness's, exhaust parts, etc XJ's are cheap in my area and very populated at the junkyards. wranglers not so much
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Old 04-03-2012, 11:40 PM   #4
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Depends on a few things:

What year is your 2.5L? 1987-1990 you have to swap the whole harness, 1991-1995 you can use the existing harness, just have to wire up the new injectors.

Would you rather swap in an engine or buy a Jeep with the 4.0 already in place?

Even so, you have to get bigger tires for the 4.10 gears. Manuals are 3.07 and autos are 3.55 I believe, for the 4.0, whereas the 4 cyl got 4.10's. Otherwise you'll be over-revving your 6 cyl. You are obviously going to need to swap in the AX15 and matching NP231J. And the computer, as well as weld on new mounts and whatnot.
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Old 04-04-2012, 10:20 AM   #5
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Drive it till the 4 banger gives up then drop in a 350/350 combo and go wild.
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Old 04-04-2012, 10:20 AM   #6
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I had been wondering about the rear diff. I am running 31's atm, could I swap the gears from the doner XJ? I know this is a lot of work, but sometimes the process is half the fun.
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Old 04-04-2012, 10:25 AM   #7
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Depends on what gears are in the XJ axles. 3.55 and lower won't swap into a 4.10 carrier.

^^That's going to be hard, especially since the 4 cylinders will run forever.
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Old 04-04-2012, 12:05 PM   #8
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yeah if mine dies i may get a 350... but the 4cyls run forever so good luck with that... but it would be easier to sell your jeep and just buy one with a 6cyl
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Old 04-12-2012, 07:47 AM   #9
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Not really reviving a dead thread since it is only a week old but I need some clarification on this.

I have a '93 with a 2.5 and a manual transmission. After driving it for the first time a few weeks ago I was really disappointed on the highway. I need an engine that can handle driving at 75 as well as offroad. The 2.5 cannot. You guys are saying the same year Wrangler with a 4.0 is a different beast? I was hoping I could simply drop in a 4.0 but you are saying I would have to replace the transmission and rework the gears as well?

If it requires that much work would I just be better off selling it and buying one with a 4.0?
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Old 04-12-2012, 07:51 AM   #10
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Yes, Yes and Yes.
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Old 04-12-2012, 12:52 PM   #11
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You can't hold 75 on your 2.5? What size tires? What gearing? When was the last tuneup?

Mine holds 70 no problems, if I push it a bit more I'll roll 75 easily, on 29" tires. It did fine with 31's as well on stock gears.
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Old 04-12-2012, 05:24 PM   #12
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It is stock. I can hold 75, with my foot nearly buried. Any hills and the speed slips. Keep in mind that this is in Colorado with thin air. I burned 3/4's of a tank of gas between Denver and Colorado Springs trying to maintain 75-80 when returning from DIA.

It does fine in town, but I-25's speeds are a struggle.
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Old 04-12-2012, 09:34 PM   #13
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start looking for one with a 6 cylinder, you would need one as a donor anyway
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Old 04-12-2012, 09:39 PM   #14
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auto trans 6 cylinders are 3.07 gears. cherokee with 4.0 and auto are usually 3.55-3.73 gears.
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Old 04-12-2012, 10:32 PM   #15
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These are the factory standards for the YJ:
2.5L manual - 4.10
2.5L auto - 3.73
4.0L manual - 3.55
4.0L auto - 3.07

Xjs
3.07 - used with 4.0L engine / manual transmission
3.31 - only available on older (pre87?) 2 door XJs with "Fuel Economy" package
3.55 - used with 4.0L engine / automatic transmission
3.73 - found in some XJs with the towing package
4.10 - used with 2.5L engine usually, and older XJs with the "Off-Highway Vehicle" package.
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Old 04-13-2012, 02:40 AM   #16
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If I can find a good deal on a 4.0 with a manual transmission, will they bolt right in or am I looking at relocating mounts?
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Old 04-13-2012, 06:42 AM   #17
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Mounts are different so you'll have to weld in replacements.

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