How good is the 4.2 liter?

[SLP0313]

Hey guys,

I'm in need of some help. I'm currently looking at a 90 Jeep wrangler with the 4.2 liter. It's an automatic with about 99k miles on the stock motor. I'm just used to seeing Jepps with the 4.0 and not the 4.2. I was trying to do some research on this motor and didn;t have any luck coming up with anything. So can anyone give me any input on this engine? Is it agood? Will it last just as long as the 4.0 if it was taken care of?? Any information will be greatful!!!
Thanks,
Mike

 

[west747]

if you dont mind the fact that it is carborated..it is a great motor. tons of low end tourque. and it is fairly reliable.

 

[Craig]

Don't know much about the 4.2L but I was out on a trail with a guy that had one. He kept stalling on the steep hill climbs because it was carburated.

 

[Bounty__Hunter]

It's a good motor and just as reliable as the 4.0L for longevity, but as mentioned the carb is problematic. They don't like to idle and stall easily on inclines. It's possible to rebuild the stock Carter carb and have luck, but it's best to replace it with a Motorcraft 2150 or Weber. The Motorcraft performs as well or better than the Weber at half the cost.

So, if you don't mind having to do some carb work down the road, it's just fine. Otherwise hold out for a '91 or newer that has FI.

 

[jay79cj7]

I have a 4.2, and it's more than enough to move my CJ around. The carb thing is a nuisance sometimes, but there are ways to improve it. Comparing stock specs, the 4.0 has alot more HP, and should get better fuel economy.

 

[chinard]

Need new brakes... argh!

The 4.2 motor is otherwise known as the AMC 258. You might have better luck searching for info that way.

Anyways, the 4.2 is a great durable engine thats easy as hell to fix when it breaks. Not too fast, but it has GOBS of low end torque.

Typically 4.2's in jeeps are known for having flakey carburators. This is an easy problem to fix... Replace the carb with a better one. So far the most popular replacements have been Weber, Motocraft, and Holley.
Keep your eye on local emissions requirements before picking a replacement carb tho.. The Weber for example is illegal for highway use in california... but then again, what isn't these days!

There are a few fuel injection retrofit systems for the 4.2, but they tend to be more expensive than actually swapping your engine in the first place.

 

[chinard]

What IYO do you think is a good vanity plate for a jeep?

Oh, i almost forgot to mention.
The 4.0 and the 4.2 are almost exactly the same engine block.
The main difference between the two is the bore/stroke, and the head design.

The two engines are almost completely interchangable and swaps are easy cause they use the same mounts.
There's even a 4.0litre head swap project for the 4.2 which apparently adds a whole pile of HP...

 

[Tug-n-pull]

Very good engin. tug

 

[skyjeeper]

the 4.2 is great. i have an 89 yj. i had lots of problems even after rebuilding the carter carb. after i replaced it (with an entirely to large of a carb. almost twice the size needed. recomend doing some research before picking your carb.) i haven't had any major problems. i've got over 220k on my engine. no rebuilds that i know of.
got a 4L head to put on after i build the engine up and go to propane.
i've heard the head will add anywhere from 20-40hp (usually 40. and one lofty proposal of 80).

 

[pezzo33]

I cant complain. When my jeep was stolen 2 months ago it had 273,000+ miles on the original engine, no rebuilds...and it ran strong. never got stuck off roading, adn i beat on he think..beat on her hard

Got a weber carb, was the best thing I ever did. Only time I stalled was when i fell over on her side

 

[Snitty]

if you DO add the 4.0 head, there are a bunch of modifications that must be done along with it.. nothing tough to do, but important things... and it DOES add a good amount of power... the highest figure i've seen was 40 hp

 

[skyjeeper]

yeah i've seen a bunch of articles describing what to do. most of it is plugging un-neede coolant channels. just have to make shure you plug the right ones.
that would be a horrible mess.

 

[Jeepster05]

back to the topic on how good the 4.2 is. If you want u joint breaking torque but not a lot of top end speed then the 4.2 is awesome. I have a 4.2 in my 90 YJ and love it. I don't really care about it being carbureted but it is a little hassle. As a perk the things sound awesome with a flowmaster on em.

 

[jprtroy]

Best thing for the 4.2 is the Mopar Multi-port Fuel Injection! A little pricey, but I can attest to it's ability to run on it's side! Stalling is a thing of the past whit the MPI!