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Unread 10-16-2013, 09:45 PM   #1
shansjeep
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1990 YJ Wrangler 
 
Join Date: Oct 2013
Location: Denton/DFW, Texas
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Quick Help Please

I just bought a 1990 YJ from a guy who was doing an engine swap but didn't know what he was doing. He was using a 98 TJ donor motor and sold it to me. He insists there was a 4.0 in it. It was a 4.2 258. It had to be, right? No 4.0 1990s were factory? I bought a 4.2 and am going back to stock and need to make sure. I ran the vin. Just need assurance that I'm not going to get in over my head.

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Unread 10-16-2013, 10:20 PM   #2
Tom95YJ
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Quote:
Originally Posted by shansjeep
I just bought a 1990 YJ from a guy who was doing an engine swap but didn't know what he was doing. He was using a 98 TJ donor motor and sold it to me. He insists there was a 4.0 in it. It was a 4.2 258. It had to be, right? No 4.0 1990s were factory? I bought a 4.2 and am going back to stock and need to make sure. I ran the vin. Just need assurance that I'm not going to get in over my head.
87-90 were 4.2l 91-95 4.0
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Unread 10-16-2013, 10:26 PM   #3
shansjeep
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That's all I found, too-but with Jeeps there are sometime "exceptions." Thank you for your reply. He just insists it was a 4.0, and the wiring does look factory, so I panicked. Going to pick up my engine Friday to start our first swap and rookie build.
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Unread 10-17-2013, 09:04 AM   #4
laybackman
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This might help;

http://www.jeepforum.com/forum/f8/id...ngine-1383352/
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Unread 10-17-2013, 09:44 AM   #5
shansjeep
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Grrrr. Thank you laybackman! Exactly why I was worried. The problem is that I don't have the original engine. I knew that info had to be out there. Thanks for the link. Really comprehensive!
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Unread 10-17-2013, 10:40 AM   #6
Que89YJ
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You do not need to buy a new engine. The TJ engine if its in good shape will work fine. It leaves you a couple possibilities. 1) get a 4.2 complete intake and swap it over. Get the MPFI stuff from a 91-95 and use it or do the OBD2 from the TJ. If you have a known good engine then you are 1/2 way there. Fill out your info and we might be able to direct you to some parts in what ever you decide.
Nice link Laybackman!
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Unread 10-17-2013, 11:07 AM   #7
zeus87gn
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Quote:
Originally Posted by Que89YJ View Post
You do not need to buy a new engine. The TJ engine if its in good shape will work fine. It leaves you a couple possibilities. 1) get a 4.2 complete intake and swap it over. Get the MPFI stuff from a 91-95 and use it or do the OBD2 from the TJ. If you have a known good engine then you are 1/2 way there. Fill out your info and we might be able to direct you to some parts in what ever you decide.
Nice link Laybackman!
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Unread 10-17-2013, 11:15 AM   #8
laybackman
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Quote:
Originally Posted by Que89YJ View Post
You do not need to buy a new engine. The TJ engine if its in good shape will work fine. It leaves you a couple possibilities. 1) get a 4.2 complete intake and swap it over. Get the MPFI stuff from a 91-95 and use it or do the OBD2 from the TJ. If you have a known good engine then you are 1/2 way there. Fill out your info and we might be able to direct you to some parts in what ever you decide.
Nice link Laybackman!
Thanks Que! How you feeling?

The search feature is the most unused tool that JF provides. If how to use that feature is not part of the FAQS section of each JF it should be. I knew I read the answer here on JF but did not have the link. The search feature led me to that link.

To the OP; I would go with one of the MPFI swaps that Que pointed out.

Why go backwards technology-wise if you are not adept at playing with engine timing and carb adjustments? Let's not forget the additional HP and better gas mileage and longer engine life also.
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Unread 10-17-2013, 12:03 PM   #9
Que89YJ
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Doing much better thanks. I can enjoy cold beer and hot moo now. x2 with the MPFI. The engines are so close that doing the conversion is a little bit of work but with a little effort and the forum, you would seriously have no problem doingh it.
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Unread 10-17-2013, 10:33 PM   #10
shansjeep
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So I will be straight up-I am a Jeep girl from way back and have read the forums for years. My girlfriend of three years is a kicka** mechanic but doesn't know Jeeps. I wanted to use the engine we have, but things don't match up and she freaks out over all the swapping and upgrades Jeepers create. She wants to go back to stock 4.2 because its easiest. Since I don't know how to actually do the work, but can only tell her in theory, what's a jeep girl to do, lol? I just want it running and figure once she's a Jeeper too we'll swap back later. You guys are awesome. Love the jeep community. I'll be asking more later about the shackle lift the guy did to get 33s on it. I'm worried about the gear ratio.
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Unread 10-17-2013, 10:42 PM   #11
BrandonYJReed
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Go with the fuel injection, there's plenty of info on this forum to help you. You'll be much happier with the end result.
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Unread 10-18-2013, 07:46 AM   #12
Que89YJ
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The engine is a drop in. The systems for the MPFI for the 91-95 are real close to bolt in. If your girlfriend is a good mech. she would truely have no problem with the help of the forum peeps putting the MPFI system in the Jeep. Depending on where you are at the parts to do it are with the engine you have is inexpensive. The carb system is ok, but the mpfi is a such a big improvement, if you are going to put the engine in and you are dealing with buying and setting up a carb upper end or a mpfi, the fuel injection is about the same amount of work with more reliability and power.

If you get a chance, please fill out the profile. Just curious where you are living. If you live in an emissions compliance state youmight need to go to the MPFI, the emissions from the original are impossible to get and even more impossible to setup.
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Unread 10-18-2013, 04:34 PM   #13
shansjeep
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I have tried many times to finish my profile but I never can get it to let me edit. I'm going to upgrade my membership and hope that helps. She is a great mechanic but is very nervous about trying all the upgrades. We live in a small time south of Denton TX and face severe emissions testing. I know we are going tomorrow to pick up a rebuilt 4.2 from a fellow Jeeper in Kansas. Closest one we found. In fact, the only one within driving distance. We will drop that and get the jeep running and then I hope she gets the jeep bug and will teach me how to do all the mechanical stuff I've been reading about for 20 years. This is my third jeep. The others were stock. The only work I ever did on them was maintenance and a new bestop itstall. Thank y'all so much for your support!
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Unread 10-18-2013, 06:23 PM   #14
shansjeep
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By the way, I updated my profile. Just got on the laptop. I read the forum more often on my phone app.
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Unread 10-18-2013, 07:35 PM   #15
Que89YJ
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Before you get the 4.2 you need to know that you will have to install all the emissions stuff on the 4.2. I can't stress what a nightmare the emissions crap is on the carb setup. The mpfi is a update and doesn't have the complicated emissions. If your gf can drop in a.c. engine she can do the mpfi swap. If you want. Pm me and I will talk to her. The 4.2 with just the carb is ok. There are mods to get rid of the pollution controls but if you have to go back to original our upgrade to the mpfi seriously you need to do the mpfi.
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