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Unread 03-28-2008, 10:01 PM   #1
Bwick84
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4.0 vs. 4.2

I have been searching for a YJ with a 6-cylinder for a while now. I've been looking mostly at the 1990's models with the 4.0. I came across a 1987 with the 4.2 and only 92,000 miles on the original motor.

How do the engines compare? Is the 4.2 still very reliable other than some of the carb issues that I have read about?

Do they get similar gas mileage? Any input would be greatly appreciated.

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Unread 03-28-2008, 10:03 PM   #2
igofshn
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Serious carb issues and less HP than a 2.5 4 cyl TJ. Don't waste your money. Post 91 is what you want.
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Unread 03-28-2008, 10:06 PM   #3
biker8888
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i agree. major carb issues. I still haven't found the right setup for mine yet... gas mileage is pretty terrible. The 4.0 is definetly the way to go IMO. One thing I do like is the torque out of my 4.2
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Unread 03-28-2008, 10:27 PM   #4
ElvisV04290
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If you want something thats going to work with as little problems as possible, go with the 4.0. Most people I know can't understand why I got a Jeep with a carb and why I don't sell it. If you have not worked with carbs before then chances are you will not like 'em. 4.2's get less mileage than the 4.0 and produce less power, that is true. I keep mine because I like the carb (since I know them) and I wanted something not everyone has, or even wants. In the end, you are going to want a 4.0L, just my guess.

Oh, and 1987-1990 is the 4.2, 1991-1995 is the 4.0 for YJ's.
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Unread 03-28-2008, 11:09 PM   #5
workinonit
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I second what elvis said. you will get more power and better mpg with the newer 4.0.. I just found my 90 4.2 pretty cheep at the time. And I love it!! but as soon as I get the funds I am going to do the 4.0 swap.
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Unread 03-28-2008, 11:15 PM   #6
Blazin Den
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If you come across a good deal on one with a 4.2 go for it. You can always do the 4.0 motor swap or even just do the 4.0 head conversion.
I was looking around for a yj with 4.0/automatic in it myself but bought one with the 4cyl/ax-5 because i got it so cheap.
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Unread 03-29-2008, 06:24 AM   #7
Bwick84
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Thanks for all the great advice. That is kind of what I thought. This Jeep just happens to be in great shape and you don't find 20+ year old vehicles with only 90K miles on the original motor very often. I don't think I've even been able to find a 4.0 with less than 100K. I think I will just hold out for a 4.0 unless I can talk him down and get it for really cheap. Thanks again.
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Unread 03-29-2008, 06:37 AM   #8
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There is nothing wrong with the 4.2 except the crappy carb on later models. Jeep used the motor for 20 years for a reason. Sure, a 4.2 doesn't have the hp of the 4.0, but it has unmatched bottom end torque that comes off nearly off idle. The 4.2 is rated at 210 ft lbs @ 2000 rpm compared to the 4.0 which is rated at 220 ft lbs @ 4000 rpm
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Unread 03-29-2008, 06:43 AM   #9
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Quote:
i agree. major carb issues. I still haven't found the right setup for mine yet...
solution is PROPANE. www.gotpropane.com I did this to my samurai. Best mod I ever did. purrs like a kitten.
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Unread 03-29-2008, 06:46 AM   #10
Brandon_YJ
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The 4.2 is a fine engine with plenty of power out of the hole.
I purposefully got a 4.2 with a carb. Sure they can be finicky, but the cost of fixing somehting if it goes bad is much lower than any computer controlled engine.
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Unread 03-29-2008, 07:13 AM   #11
roadyrob
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when I was looking for my heep, my main priority was a solid body and frame. i found an 87 that had been a motor home tow behind, completly stock, with a poorly running 4.2. swapped out the carb and ignition for a weber and hei. now it runs great, gets about the same gas milage as the 4.0 ( 14-15 around town, 18 highway)
its easy to work on and has plenty of power. the HP and torque are at low rpm's where you can use it. great motor if they are set up right.
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Unread 03-29-2008, 07:30 AM   #12
Bwick84
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How much did the weber carb cost you roadyrob? I've never really worked with carbs before, are they hard to install/work with?
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Unread 03-29-2008, 08:30 AM   #13
roadyrob
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you can get a weber kit for around 300.00. ( I got mine off ebay from a private seller that decided not to use it for 200.00 ) the kit is complete w/linkage, adapter and air cleaner. the instructions are easy to follow. you really need to do the hei distributor also. I got mine from crt on ebay, another 200.00. don't count the 4.2 out, if you can get a deal on a solid jeep, I would use the need for upgrades as a bargaining (sp) point, dollar for dollar a 4.0 is a better deal.
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Unread 03-29-2008, 09:59 AM   #14
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If you can get a low milage 4.0.....it's a great motor, but you do have a lot more stuff to contend with when it starts to go south.

A nicely set up 4.2 rocks! The low end torque is awesome & they are about as complicated as a hammer to work with. & about as reliable, too.

With equal condition motors, I'd base my decision on a rust free body & drivetrain milage....as fixing body work or re-furbishing running gear can get pricey in a hurry.
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Unread 03-29-2008, 11:52 AM   #15
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Quote:
Originally Posted by Beachcruiser View Post
..they are about as complicated as a hammer to work with. & about as reliable, too.
And alot of times, that's the only tool you need to work on it.
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