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Old 03-02-2012, 06:20 PM   #1
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4.2 swap to 4.0

Does anyone know if a 4.0 from a 1998 Grand cherokee will work in a 1988 wrangler with 4x4 5 speed manual trans? I currently have a 4.2 If so.... is there anything I need to to change?

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Old 03-02-2012, 07:40 PM   #2
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You will need the wiring harness and the computer. Tranny should bolt up. But just swapping the 4.0 head with the MPI is a awesome upgrade!

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Old 03-02-2012, 08:12 PM   #3
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i agree with BDK. a top end swap is your best bet. the 258 is a great motor especially fuel injected.
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Old 03-02-2012, 09:25 PM   #4
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Well... my 258 has a lower end knock and serious blow by. Thats the main reason for the swap. Should I just rebuild and install a 4.0 head?
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Old 03-02-2012, 09:54 PM   #5
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the grand chrokee has a security system that will cause you problems find a chrokee cpu. I did the swap in my cj, and used a 92 chrokee that I got for a hundred bucks. rebuilt the motor ysed the 5 wire to fire method of wiring. best thing i ever did.
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Old 03-03-2012, 11:06 AM   #6
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Quote:
Originally Posted by red-jeep View Post
Well... my 258 has a lower end knock and serious blow by. Thats the main reason for the swap. Should I just rebuild and install a 4.0 head?
thats what i would do, but its up to you. a lot of guys would just drop the whole 4.0 in. theyre cheap and plentiful and you could find a used one that still has a lot of life left in it. if you want "brand new" though rebuild either one. i guess its just a matter of how much money you wanna spend.
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Old 03-03-2012, 05:40 PM   #7
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Okay..... So decided to rebuild and do the 4.0 head conversion. I read that I will have to close off (2) water holes using hi-temp epoxy, Is this true? And do I need a 4.0 intake and exaust manifold? If so will my carburator bolt up?
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Old 03-03-2012, 05:45 PM   #8
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Here you go chief!
4.0 Head swap

You can keep the carb and reuse the 4.2 intake, but need to swap in the 4.0 exhaust manifold. Keep the 4.0 intake mani for doing a MPI injection swap later.
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Old 03-03-2012, 05:58 PM   #9
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Thanks Bdk! I just read that post on the conversion. Looks simple enough. Hoping to start this project next week. I will keep you guys updated.

Thanks Again
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Old 03-03-2012, 09:18 PM   #10
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a picture is worth a thousand words. good job diggin that article up BDK
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Old 03-18-2012, 07:39 PM   #11
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So I went ahead and rebuilt my 4.2 and put a 4.0 head on from a 00 GC. Ending result was amazing! Even though it has NOT broke in I see a big change in power. The 4.2 intake did work as well as the 4.2 exaust manifold. But it wasnt easy. I had to make a couple modifications in order for it to work. Grinding a couple corners, utilizing oversized washers and making my own gasket. Also learned that my yj has also been "nutterd". I had never heard of that till now. So now I want to take off all the emissions stuff that is on there. I feel that all those vacuum lines are not needed since it has been nutterd. Does anyone know if i can just remove everything and plug off lines or do I need to make some changes in order to do so?
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Old 03-19-2012, 01:15 PM   #12
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Did you keep the stock carb on that? I have been looking into doing the same thing and was debating to go to a motocraft carb or the fuel injection.
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Old 03-20-2012, 07:25 AM   #13
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I did keep the stock carb for now. In the near future I plan to get a weber carb or go injected.
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Old 03-21-2012, 08:11 AM   #14
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Quote:
Originally Posted by red-jeep
I did keep the stock carb for now. In the near future I plan to get a weber carb or go injected.
Don't bother with a weber, for the cost of one just swap in a mpi from a Cherokee.
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Old 03-21-2012, 03:25 PM   #15
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So what do I need to do for that?
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Old 03-22-2012, 01:47 PM   #16
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So what do I need to do for that?
Well you have most of it, I will find the link for you a bit later. Have to hit up dollar burgers at the vfw.
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Old 03-23-2012, 09:05 PM   #17
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Originally Posted by BDK

Well you have most of it, I will find the link for you a bit later. Have to hit up dollar burgers at the vfw.
I have it all. I just picked up a complete, running GC for $500. It has a lower end knock. I'm gonna take what I want and part out the rest.

I also had another idea. What do you know about those AWD transmissions? Have you ever seen an AWD YJ? It it possible?
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Old 03-23-2012, 09:31 PM   #18
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Quote:
Originally Posted by red-jeep

I have it all. I just picked up a complete, running GC for $500. It has a lower end knock. I'm gonna take what I want and part out the rest.

I also had another idea. What do you know about those AWD transmissions? Have you ever seen an AWD YJ? It it possible?
From what I hear they are solid trannies. I have seen a couple TJs with them.
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Old 03-25-2012, 11:35 AM   #19
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Originally Posted by BDK

From what I hear they are solid trannies. I have seen a couple TJs with them.
I have been looking for info everywhere for this mpi swap. I found kits and everything else. I have not found anything on using the mpi from another vehicle. I want to get going with this project. Help please!!!!
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Old 04-01-2012, 05:26 PM   #20
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Its really easy just google jeep 5 wires to fire, should find all the info you will need. I did a 4.0 swap in my 79 cj took me the better part of a day. But it was the best thing I ever did for the old girl.
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Old 04-01-2012, 08:23 PM   #21
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Project YJEEP

I did a 4.2 to 4.0 swap in my 87 YJ, but I got a 92Yj 4.0 with harness and computer. Still many wires to reroute.

Check out the build thread here--->Project YJEEP <---



This pic is before I finished the wiring:


Rewiring notes:




Doing the '98 OBDII swap will involve much more than I had to do. The Grand is much different from the YJ in many respects. I'd recommend getting a 91-95 4.0 wiring harness!!!

Good luck with the project.

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