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Old 05-11-2011, 04:17 PM   #1
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Unhappy YJ 4.2L swop to a CJ 4.0L

Hello everyone. I bought my first jeep. 1989 Wrangler 4.2L. Of course as soon as I get it home and correct all the vacume lines and stop the carb from dumping fuel, I find that the motor is shot. There is so much blow-by that the air cleaner is filled with oil. The sneak I bought it from hooked the breather hose up to the PCV line so when I pulled off the oil cap to see if there was any blowby there wasnt any. After I corrected the breather and hooked it up to the aircleaner it blows like a locomotive out the oil cap.
Sorry for the tangent. My question is this. I have the oportunity to buy a 1982 258ci out of a CJ. Will it fit/match/bolt up in a 1989 4.2L YJ ?

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Old 05-11-2011, 04:28 PM   #2
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cj's never had a 4.0L, they have a 4.2L. as for matching up i don't know. you'll probably have to change the Motor mounts.

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Old 05-11-2011, 05:23 PM   #3
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258 is a 4.2, so I'd assume apples to apples and such
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Old 05-11-2011, 08:44 PM   #4
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i would try and find a 4.0 and ditch the whole carb problem. but that may take some more work..
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Old 05-11-2011, 09:32 PM   #5
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Quote:
Originally Posted by cpisani89
i would try and find a 4.0 and ditch the whole carb problem. but that may take some more work..
What carb problem.... I find more problems with adding a computer to the mix. I have an '89 with a 4.2, MC carb, HEI, and no ECM or emmissions sensors. Runs like a dream. No codes to check for, and it is all much simpler to work on than an EFI set up when there is an issue. Living in FL there is also no seasonal tuning for the carb needed. The only sensors I have go to the gauges, and the only wiring under the hood, other than lights and gauges, is the alternator, electric fan, and ignition.... K.I.S.S. -- Keep It Simple Stupid. I can pinpoint a problem very quickly with this set up, and have it fixed in no time.
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Old 05-11-2011, 10:04 PM   #6
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Yea, My mistake 4.2L cj. Someone mentioned that the CJ was made by AMC and the YJ was made by Chrysler so it may not fit.
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Old 05-11-2011, 10:06 PM   #7
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In '89 Jeep was still AMC, '90 was the change.
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Old 05-11-2011, 10:09 PM   #8
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early yjs were designed and built by amc, so it should be similar.
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Old 05-11-2011, 10:17 PM   #9
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So it looks good! I did have a fleeting thought of converting to fuel injection. Factor in the wiring harness, computer and cutting a hole in the bell housing for the crank sensor etc etc. I dont have the time or money for such a project.
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Old 05-11-2011, 11:45 PM   #10
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My '87's title lists it as AMC... A sedan, lol but from what I read, Chrysler bought AMC in '87 but used up AMC's parts supply so... who knows exactly when they were actually Chrysler lol
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Old 05-12-2011, 12:11 AM   #11
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they finished using up the parts by sometime in 1990 all 1991 and newer should be chrysler. now as for the difference in blocks i believe they should be the same but if your doing that much work you can go v8. now if you stick with swaping in the cj 258 motor just mix it all up so you have as many good working parts in your jeep as possible, meaning just dont write off everything under the hood of your jeep. plus if the block your getting is in really good shape look up the 4.0 head swap for the 4.2 engine. it adds somehwere in the field of 30-40 horses, i say it should be in really good condition cuz it increases your compression.... hope that made sense.
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Old 05-12-2011, 12:19 AM   #12
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Quote:
Originally Posted by Planetisfull
Chrysler bought AMC in '87 but used up AMC's parts supply so... who knows exactly when they were actually Chrysler lol
Yeah, the agreement was in late '87 but the deal was final in late '88 from what I understand. Half of the '89 jeeps were built in '88 before Chrysler had full control as much was tied up in AMC's going bankrupt. The AMC designed 4.2 stayed in production unchanged until the retool in '90 for the 4.0. So any 4.2 will have the same mounts.
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Old 05-12-2011, 12:24 AM   #13
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You guys are the best!
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Old 05-12-2011, 01:47 AM   #14
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There is really no reason not to go for the 4.0L. It's hands down a better engine, and it's also more powerful. More torque, and more HP.

I'm sorry, but the 4.0L is not more difficult to work on...especially an OBDI model....

billytheyj is right though. It's almost the same amount of work for a v8. The nice part about tossing in a 4.0L is you can keep more of your drive train. It's still going to be pricey though.
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Old 05-12-2011, 06:18 AM   #15
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Quote:
Originally Posted by MikeMYJ View Post
There is really no reason not to go for the 4.0L. It's hands down a better engine, and it's also more powerful. More torque, and more HP.

I'm sorry, but the 4.0L is not more difficult to work on...especially an OBDI model....

billytheyj is right though. It's almost the same amount of work for a v8. The nice part about tossing in a 4.0L is you can keep more of your drive train. It's still going to be pricey though.

this.
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Old 05-12-2011, 07:23 AM   #16
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if you can do the 4.0 swap, do it. its an upgrade.

don't get me wrong though, i love my 87, carb and all, but i love carbs. i am a huge fan of the 4.0 from owning many cherokees, grand cherokees, and a 93 wrangler. the engine feeling is so much different that its like going from a stump pulling truck to a 0-60 hot rod though. the 4.0 is just waiting for you to floor it so it can rip up the rpm range while the 4.2 is very very happy riding in the lower range and idling up hills with no accelerator input.

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