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Hello all, I'm in desperate need of some help with engine wiring. I have a 1990 YJ with a throttle body fuel injection 2.5L and i'm in the process of swapping in a 4.0 from a 94 YJ. I have the engine, ax15, correct transfer case, engine mounts, engine computer, and wiring harness, so everything is there to do the swap. The main issue i'm having is the wiring. Do I need to strip the wiring and start from scratch? Is there a way to use my existing TBI harness? If anyone has done this swap before and could give me some insight it would be much appreciated. - Matt
 

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:welcome: to the Forum..:wavey:

Thread moved.
 

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If you have the complete wiring from the donor jeep, use it and discard ALL of the old wiring in the jeep
 

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Yep gonna need the 4.0 efi wiring harness
Also doubt the tb system runs correct pressure for a 4.0 efi setup
Plus the 4.0 has a regulator on rail and a fuel return line


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Welcome to the Forum Mcshafer96,

In order to make a clean wiring installation you'll need a Factory Service Manual for the '90 and the '94 YJs.
As Gottagofast states, you'll need the entire '94 engine harness and PCM. The lighting harness may or may not be the same. The underhood harnesses separate from one another at the plug that goes into the firewall, near the brake booster.
You need to insure the wires are the same for the '94 and the '90 harnesses where the engine harness plugs into the firewall. If not, you'll need to depin them and move the '94 wires to the '90 position.

Find a post by Got it at last. In his signature there's a link to several manuals. Click on the link in his signature and then click on the manuals that most closely match the years that you're dealing with.
Post some pics of your swap.

Good Luck, L.M.
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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Manuals below, Good luck with the swap.
 

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To be clear. I am suggesting EVERY WIRE IN THE JEEP be changed not just the engine harness... also the instruments, computer, etc.... no guessing that way...
 

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To be clear. I am suggesting EVERY WIRE IN THE JEEP be changed not just the engine harness... also the instruments, computer, etc.... no guessing that way...
I forgot that the gauges are different between the '90 and the '94. Plus, the '90 has a mechanical speedo drive and speedo head. In the '94, those are electronic. You'll need gauges, speedo and wires plus the speedo drive on the transfer case.
There may be a work around, but I'm thinking the PCM (from the '94) might need a signal from the speedo. I'm not too sure about that though.

Other posters may be able to add to this.

Good Luck, L.M.
 
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