4.0L swap - wiring help - JeepForum.com

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post #1 of 7 Old 10-22-2008, 03:59 PM Thread Starter
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4.0L swap - wiring help

Hey. I have found many threads about 4cyl to 6cyl swaps, but have not found the info I need.

To start I am preparing to swap my 90TBI 4cyl/5sp with a 92 4.0/5sp. My donor driveline came from a 92 YJ. Unfortunately, I do not have the engine wiring harness or the ECM for this engine. Can I use a wiring harness from a XJ as long as it came from a manual transmission jeep? Which years would work best? How will using a XJ engine harness affect the rest of my YJ wiring. Will my fuel pump be reusable?

Thanks in advance for all your help and suggestions.

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post #2 of 7 Old 10-22-2008, 06:31 PM
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There are differences to the harness and a few differences in the firmware that's in the computer. If you can get a wiring diagram of the XJ harness, you should be able to make sure that you have the correct wires coming into the cabin. One of the differences will most likely be the fuse block itself - I believe they're different enough that the inside and outside halves don't fit together.

The XJ ECM will work, but it'll keep telling you that some things don't work, like the electric fan, etc. because of the data set it was flashed with. I don't think you'll run across any dealers that are able to re-flash it for you, so you generally need to put up with those codes it generates.

I looked at doing that one time but decided it was easier to get a YJ engine bay harness than to clean up an XJ one to make it fit - I did use the XJ computer though, and it continues to work today. It saved me days of work & probably weeks of debugging.
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post #3 of 7 Old 10-23-2008, 06:25 AM Thread Starter
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OK. Thanks. I guess I keep searching for a YJ wiring harness.

Does anyone know if I can reuse the TBI fuel pump from the 2.5 for the 4.0MPI?
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post #4 of 7 Old 10-23-2008, 07:10 AM
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It is my understanding that for the fuel pump as long as it is from a 91 or later 2.5 fuel injected motor it will work for a 4.0 swap. I just swapped a 92 4.0 into my 95 that had a 2.5 and the fuel pump works fine so far. I posted the schematics for both the xj and yj pin and block set ups in another post. They were for a 95, but the mechanic said in that year they were almost the same.
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post #5 of 7 Old 10-23-2008, 08:39 AM
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You can use XJ harness and ECM without any codes, the electric fan doesn't show any code when not hooked.
I'm using harness out of 93 XJ and 95 XJ ECM, the only code I'm getting is the alternator field, that b/c I'm using CJ alternator.

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post #6 of 7 Old 10-23-2008, 05:28 PM Thread Starter
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I think I've just located a YJ dash and engine harness and ECM so will probably use those. Thanks for the help guys.
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post #7 of 7 Old 09-07-2011, 01:08 PM
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im doing a 1993 yj 2.5 ax5 swap 95 4.0 h.o out of a grand cherokee with the automatic transmission how can i wire the tranny harness into the factory harness i already added the two injector wires in just need the transmission hooked up
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