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Thread: 2.5 to 4.0 Conversion

  1. #1

    Default 2.5 to 4.0 Conversion

    Guys, Has anyone converted a 2.5 to a 4.0? I have a 99 TJ 2.5 and found have a 02 4.0 engine to rebuild. Some questions I have are "Will the wiring harness and ecm... work for the 4.0 motor? I understand the manual transmission won't - but plan on replacing that as well. Also - I am interested in stroking this motor or any other suggested upgrades that might boost the torque and/or HP. Any advice with changing this over would be great. Thanks in advance.
    99 Wrangler
    2002 Hayabusa
    1997 Ski Doo 700 Triple
    Makers Mark Drinker

  2. #2

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    I have replaced a 2.5 with a 4.0, but I had the entire Jeep to swap everything over (frame, suspension, tub was trashed). I basically swapped a 4.0 engine/trans/wiring/interior into 2.5 frame and tub. It was a easy swap with motor frame mounts and the steering shaft frame mount being the only major things that had to be changed. You are going to need a lot of small parts as well as wiring and ecm to do it with just the motor. If you have any specific questions I will do my best to answer them.
    99 TJ 4.0, 9" Spooled rear, 44 Detroit front, 5.38's, Atlas 4.1, 38 TSL's, 5.5 RE, caged, 8274-50, bunch of extra metal...

  3. #3
    -DETOUR- Tim's Avatar
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    if i were me, i would swap in a 305,318.. something that would prolly be more bang for the buck and trouble depending on what you really want.
    There are no shortcuts to any place worth going.

  4. #4
    Registered The_Borg_Cube's Avatar
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    Highlands Ranch,Colorado
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    eh 4 wheeling is not a high horsepower game. stock 4.0 is all the engine you'll ever need. just dont load your rig down with 1500 pounds of stuff.

  5. #5

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    I would suggest to do a realistic comparison of what it costs in money and time to do the conversion vs. selling the 2.5 Jeep and buying a 4.0 Jeep.
    05’ Blue TJ Rubi (auto) / RE 3.5 Super-Flex / Bilstein 5100’s / Anti-Rock / JKS BL & MML / 33x13.5 Toyo MT / 15x10 Eagles / Jeeperman Skidz / Skid Row Engine Skid / MileMarker Winch / RockHard Front and ProComp Rear Bumpers / SentryKey+Ravelco / CO2 Tank / CB+HAM / Centramatic balancers

    92' YJ -Lifted, locked, and sold...

  6. #6
    Registered
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    pa 18702
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    I know on a YJ you can reuse the stock wiring by adding two wires for the two extra injectors.Still need the 4.0 computer.Look around and see if it is the same on a TJ.

    Its alot easier than people say/think it is.Most people with an opinion never did the swap and just re-say what other people say.

  7. #7

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    Thanks as well - I will look into this.
    99 Wrangler
    2002 Hayabusa
    1997 Ski Doo 700 Triple
    Makers Mark Drinker

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