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Unread 02-19-2013, 06:51 PM   #1
BOYF94YJ
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1994 YJ Wrangler 
 
Join Date: Jan 2013
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Need info on engine swap 94 YJ 2.5L to 98 4.0L

My 4 cylinder finally died in my 94 YJ... Purchased a 4.0L & AX15 from a 98 TJ. About to rebuild the engine. Looking for information about the computer & a couple other things. I have the wiring harness from the engine but no ecm. Trying to find out if I have to use the computer from a 98, if so will it run my gauges on my dash? Also if I could use the ecm from a 94 for a 4.0L? I plan on using my transfer case. It's a 21 spline, need to know what to swap out so it bolts to the AX15? Any help will be greatly appreciated

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Unread 02-19-2013, 07:47 PM   #2
hypernoodle
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1989 YJ Wrangler 
 
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IIRC, you should be able to run your existing ECU with a couple of wires added. There are plenty of write-ups.

For the t-case, I'm a fan of the 231. Get the SYE kit and you will fall in love, too.
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Unread 02-19-2013, 08:02 PM   #3
BOYF94YJ
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I'm going to go with SYE. Just need to find out what has to be swaped to make it a 23 spline.
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Unread 02-19-2013, 08:41 PM   #4
hypernoodle
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The 231 should mate right up to the AX15
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Unread 02-22-2013, 07:22 AM   #5
-jb-
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Quote:
Originally Posted by BOYF94YJ View Post
My 4 cylinder finally died in my 94 YJ... Purchased a 4.0L & AX15 from a 98 TJ. About to rebuild the engine. Looking for information about the computer & a couple other things. I have the wiring harness from the engine but no ecm. Trying to find out if I have to use the computer from a 98, if so will it run my gauges on my dash? Also if I could use the ecm from a 94 for a 4.0L? I plan on using my transfer case. It's a 21 spline, need to know what to swap out so it bolts to the AX15? Any help will be greatly appreciated
You'll want to run the ecm for the 98 since it's an OBD2 motor. Unless you swap things out to OBD1 on the motor and run a OBD1 ecm. If you run your tcase then you must swap in a 23spline so it mates to the ax-15. While you are there you might as well through in a SYE. Get a FSM for your vehicle and the 98 vehicle and check the wiring diagrams to make sure pinouts will match up
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Unread 02-22-2013, 02:00 PM   #6
ratmonkey
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to run it as an obdi you'll need to change a couple sensors and add the fuel return system found on obdi 4.0's.
you can use your existing 2.5l WIRING HARNESS with a couple sets of wires added for the injectors. but you can't use your existing ecu as it doesn't have the two extra injector drivers needed for the fuel injection. you'll need an obdi computer for that.

you can not use the obdii harness and computer. unless you want to change up a bunch of the interior wiring and add tj gauges or aftermarket gauges to it.
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Unread 02-24-2013, 02:18 PM   #7
LaddieHanus
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Quote:
Originally Posted by BOYF94YJ View Post
I'm going to go with SYE. Just need to find out what has to be swaped to make it a 23 spline.
You need swap the input gear on the TC Since you are putting in a SYE you are most of the way to replacing it. For my 89 I paid over $100 for the gear a number of years ago.
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