Can I swap a 2004 vintage 4.0 in my 91 YJ? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 09-13-2006, 09:22 PM Thread Starter
 
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Can I swap a 2004 vintage 4.0 in my 91 YJ?

Howdy. My 91 YJ 4.0 engine has a lot of miles on it and needs a lot of work (the lifters recently failed). I've got the head off and I might rebuild it, but I'm considering a salvage yard 4.0. There's lots available in my area out of late model Cherokees and Grands (with relatively low miles). Can anybody tell me the differences between a 91 YJ 4.0 and one out these 2000-2006 vehicles? THANKS!
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post #2 of (permalink) Old 09-14-2006, 06:33 AM
 
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Re: Can I swap a 2004 vintage 4.0 in my 91 YJ?

Yes you can. BUT...The difference is The 91 is OBD 1 and anything 96 or later is OBD 2.

You either have to swap all the fuel injection, ignition, charging system and other emmisions stuff from your 91 to the new engine OR get all the wiring and computers that go with the new engine including some under dash stuff. If you do that you'll need to install another O2 sensor as well. There may also be issues with the computer looking for input from the transmission of the donor vehicle.

The easiest way would probably be to take the long block from the newer vehicle and keep your YJ OBD 1.
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post #3 of (permalink) Old 09-14-2006, 03:40 PM Thread Starter
 
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Re: Can I swap a 2004 vintage 4.0 in my 91 YJ?

Thanks for the reply, jeepete. I would plan on keeping the manifolds and injectors off of the old engine. I'm still concerned about mounting bosses for accessories, holes for sensors (like crankshaft position) and stuff like though. Do you know if all of this stuff is compatible throughout the years? As long as all of the old sensors fit on the new engine and everything bolts up OK, it should be an easy swap....
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post #4 of (permalink) Old 09-14-2006, 06:40 PM
 
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Re: Can I swap a 2004 vintage 4.0 in my 91 YJ?

Now that I think about it more, I believe there are differences in the heads and your 91 manifolds may not fit right. Whether you can put 91 injectors in a, say, 2003 manifold, I don't know but I think there's a good chance you can.

The CPS is on the bellhousing, you didn't mention swapping that so I assumed you didn't intend to. If you want the new transmission that raises other issues.
The O2 sensor is in the exhaust system, most other sensors are in the intake manifold/throttle body assembly. I'm pretty sure you could find places for other misc. sensors, oil pressure, water temp etc.



Hmmm... it may not be as simple as I first thought! I'd recommend asking around on some other Jeep boards if no more info is forthcoming here.
I still say it can be (and most likely has been) done.
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post #5 of (permalink) Old 09-14-2006, 06:41 PM
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Re: Can I swap a 2004 vintage 4.0 in my 91 YJ?

Everything, with the exception of the crank sensor is either on the manifolds or distributor ..all of which you're swapping. Like you said, the other stuff like your accessories and such could be PITA issues.

I believe that your crank sensor is on the bellhousing, no?
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post #6 of (permalink) Old 09-14-2006, 07:28 PM Thread Starter
 
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Re: Can I swap a 2004 vintage 4.0 in my 91 YJ?

You guys are right about the Crank Sensor: it's in the bellhousing on my 91, and I don't plan on swapping the trans (I already put in 2 Jasper Rebuilds). And I guess that the other sensors are, indeed, on the intake and distributor. It's just a question of compatibility between a newer head and older intake. Also, mounting bosses on the heads and block could deviate. There's gotta be a way to figure this out...
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post #7 of (permalink) Old 09-14-2006, 07:37 PM
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Re: Can I swap a 2004 vintage 4.0 in my 91 YJ?

if you wanna use the newer engine(98 up) you can. your intake manifold and exhaust manifold will bolt up to the head so all your sensors or on the old manifold they will work the accs should bolt up to. If you you wanna run a hole new engine and put your accs on it you will be runing into problems with the powersteering pump mounting diffrent on the intake. The plugs for the sensors are diffrent.
You would have better luck geting a 4.0HO out of a 92-94 xj its the same motor you have you wont need to rewire any thing every thing is interchange able and they are more reliable then the newer ones.
The newer 4.0s have head problems with them cracking between 4 and 5 cylinder in 05 they decided that an aluminum timing gear is better then steel they like to get the teeth eatin off of them from the cam
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post #8 of (permalink) Old 09-14-2006, 08:14 PM Thread Starter
 
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Re: Can I swap a 2004 vintage 4.0 in my 91 YJ?

Thanks for the detailed info!
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