1991 YJ I4 to I6 Engine Swap - Jeep Wrangler Forum
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Old 11-20-2013, 05:07 PM   #1
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Question 1991 YJ I4 to I6 Engine Swap

Hello, this is my first post and please any feedback would be greatly appreciated.

So it is getting close to Thanksgiving break for me for college and my dad and I are planning on swapping out the 4-cylinder in my 1991 Jeep Wrangler YJ and are planning on replacing it with a 6-cylinder from a 1993 Jeep Wrangler YJ Sahara model. We would've just used the 93 sahara, but the previous owners used it as a vehicle around their property so the frame and body aren't worth the repairs, however, the engine started right up and runs great without any problems. I am wondering what all will need done to make the swap as smooth as possible. We have already removed the engine and transmission from the 1993 Sahara already and I know we already need to change the motor mounts. Is there anything else that needs done before we take on this task or is there a lot more to it than what we have researched already?
Any advice and help would be greatly appreciated!

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Old 11-21-2013, 03:04 PM   #2
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You will need to use the transfer case out of the 93 as well. The wiring on the 4 cylinder is also different from that of the 6. Here is a thread that should help out 2.5l to 4.0L Swap.

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Old 11-22-2013, 05:07 PM   #3
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Thank you. Your Jeep looks nice. Mine actually has the same front and rear bumpers.
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Old 11-22-2013, 06:01 PM   #4
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you will also have to change the tach
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Old 11-22-2013, 06:06 PM   #5
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Speedo as well. Pre 91 speedo is cable driven. Post 91 has a vss and electrical speedo.

I have read about a mod to get the tach working but if you have it from the donor vehicle just swap it.
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Old 11-22-2013, 08:54 PM   #6
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Although you may be able to remove the vss sensor and attach the cable. I can't find much info on the thread size. I believe the cable thread is 7/8-18 don't know what the vss is.

But then the donor speedo has the miles for that engine on it so I'd swap it anyway for that reason.
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Old 11-23-2013, 08:29 PM   #7
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So the speedometer on my 91 is cable driven?
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Old 11-24-2013, 07:24 AM   #8
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I believe 91 was the last year for the cable drive.
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Old 11-24-2013, 08:10 AM   #9
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I did the swap earlier this year and it was not bad. The only issues I had was the wiring was from a 93 and I had a 95. I could not get spark until i re-did some wires in the connector under the battery.
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Old 12-03-2013, 04:10 PM   #10
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My 91 is cable driven, but I noticed that you could take out the plugin piece from the back of the transfer case. My question is, could you change the plugins from the transfer cases? I also know that they are different on the inside, but the one from the 91 fits into the 93 and it also feels as though it turns just like the 93 does. Could this work? if not then is there any way to do this without changing the speedometer?
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Old 12-04-2013, 09:42 AM   #11
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Why not just use everything from the donor yj wiring gauges in all so there no worries about it being compatible
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Old 12-04-2013, 09:42 AM   #12
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since you have the 93 donor jeep, just swap over all the wiring and gauges. It is not hard to do. I have a complete harness and gauges frim a 94 in my 88. you will also need to swap out the tailites if you do swap the harness. You have 3 main harnesses: engine, dash, and tub. Just take the time to do it. You will learn vast amounts abiut how your jeep works and is put together.
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Old 12-05-2013, 01:25 AM   #13
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Quote:
Originally Posted by Fabrokoner View Post
Although you may be able to remove the vss sensor and attach the cable. I can't find much info on the thread size. I believe the cable thread is 7/8-18 don't know what the vss is.
Could just swap tail housings on the transfer. But then might run into problems of the tone wheel vs the gear on how they mount to the mainshaft. I'm not sure if it'd work but is a possibility
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Old 12-07-2013, 06:32 PM   #14
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i thought about that as well but I wasnt sure if there would be any problems or not. We decided just to swap out the guages.=

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4-cylinder , engine help , jeep 1991 , sahara yj , swap

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