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Old 08-21-2012, 07:58 PM   #1
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Used YJ engine questions

G'Day All,

I am in the market for a manual transmission YJ 1987 - 1995 and need some cogent advice re 6 vs 4 cylinder engines. What are the pros to the 4 cyl? What are the cons? Ditto for the 6.

IIRC, the carburetor model sixes had engine carbon buildup issues. Where these problems resolved with MPI?

Aside from horsepower, is the 6 a better engine than the 4? I welcome any & all input. On the market in my area, east coast are YJs from 100k - 250k miles. I will probably not consider any with more than 150k miles. Thoughts anyone?

Thank you.

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Old 08-21-2012, 08:34 PM   #2
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I personally love my 4 cyl. I have owned both and while the 6 was a better daily driver, the 4 is much better on fuel and parts. Yes, the 4 is down on power: a few simple tricks ( electric fan, cold air intake and cat back exhaust) really wakes the little beast up. If bigger tires are in your future, plan on installing 4.88-1 gears. Offroad in low range its a wash. The 4 gets better fuel economy and is easier on parts. Yes, I am one of THOSE guys who still run a D35 ( albeit with a Super35 kit) with a Detroit locker and 32" M/T's. And have for the last 4 years with some pretty serious wheeling. My 6 destroyed the D35 on the second trip out while sitting on 31" A/T's.
Besides, 4 cyls are usually cheaper to buy and maintain. Would a 6 or 8 be nice? Heck yeah! But a bigger engine requires bigger drivetrain parts and bigger fuel and maintenance costs.
Ok, off the soapbox! In the end, its up to your preferences and wallet.

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Old 08-22-2012, 10:08 AM   #3
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Used YJ engine questions


Thank you for the response. It is appreciated

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Old 08-23-2012, 08:56 AM   #4
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I also love my 4, big gas tank I can go for days deer hunting and be fine on fuel 100 miles from the nearest gas station. Down on power a bit but with 31 and when running good I can use 5th on flat ground and roll at 75 easy. Parts are easy to find most of the time, there is 1 or 2 sensors they don't make anymore and you have to be creative, use a resitor or another sensor from another car with the same values. Thats on the early 2.5 TBI. Good luck.
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Old 08-23-2012, 09:54 AM   #5
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Remember the 4cyl has more torque than the 6. So you should be better off on the trails. Sometimes more power= spinning your tires and you going nowhere. My buddy and bro have a 6. I can go anywhere they can, might take me a little longer to get there.
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Old 08-23-2012, 11:12 AM   #6
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I've had both. My first YJ four banger got no better MPG than my straight six.

What to look for and avoid.

4.2 straight six. PITA carbed engine.
4.0 fuel injected engine that will last forever if even somewhat taken care of.
2.5 a great little engine that will last as well, but power is lacking and even if it is a four cylinder, it is not a gas sipper.
2.5 is matted up with the AX-5 transmission. It is not nearly as bullet proof as the AX-15 on later 4.0 engines.
The frenchy Puegot transmission is awful. Stay away.
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Old 08-25-2012, 10:42 AM   #7
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Thanks guys. The input is appreciated

Based on your posts I will go with an mpi 6 for the stronger x-mission.

Again, thank you for thoughts.

NC Outer Banks
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Old 03-04-2014, 04:40 PM   #8
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Used YJ engine questions & YJ purchase.

To all who responded to my request for advice, many, many thanks.

Here some 18 months later, is the result of my 6 month search for a YJ ending with a 2.5L 5 speed with a great running engine (good compression, no valve clatter and no oil consumption).

Some minor body rust was easily repaired with boat building expoxy...I am not a welder, but I know how to use marine epoxy and I do not like Bondo. PM me if you have questions.

In sequence, the photos document the changes I have made to this 1993 S model since February, 2013 using salvage yard parts.

Work done:
New body mounts with 1 inch bodylift...a real PITA, busted knuckle chore.
New lower steering shaft.
Rust repair to d/s quarter panel & floorboard.
New CJ radiator, H20 pump, salvage yard 130 Amp alternator, & cone air cleaner as OEM would not fit behind CJ grille.

BTW: That is a brush paint job using 8 coats of Rustoleum safety red. At 5 feet not so pretty but a lot of the imperfections will be removed by a final 1,500 grit hand wet sanding, compounding, waxing & buffing. I await warmer weather.

Next major change will be a CJ dash with OEM speedo, Speedhut 4" dual oil/volt gauge & retro-radio with the windshield painted to match the body.



Outer Banks, NC
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