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MJ 4 cyl. owners. Please chime in


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I'm currently looking for an MJ. I've owned a cj, yj, & a few XJ's in the past but they all had the 6 cyl. Which I really loved, but I have found a truck that I like that has the 4 cyl.,. My question is.... was there a carb. & fuel injection model? & what are the other up's & downs of the 4 cyl? The truck I found is a 89. Thanks in advance for any help.

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I believe the 2.5L was MPI for that year... They were never offered in a carb on the MJ's. Its a peppy little engine, but if you are really looking forward to that 4.0L power, I'd wait for one of those, or swap one in if the truck is worth it. Really reliable little sucker, and get around 20 MPG normally.

 

Rob L.

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2.5 liter...

 

carb in 84 to early 86 cherokees. fuel injected in ALL comanches. 86-90 was TBI fuel injection, 91-92 was multi-port fuel injection (MPFI)

 

 

motors are strong, they last. decent gas mileage, but you can tune a 6 cyl to get the same mileage as a TBI 4 cyl. mpfi 4 cyl will get a steady 18-22mpg, more if you drive like a grandma.

 

if the truck is nice, the lack of power can be resolved later. there isn't much more than an aftermarket header available for a 4 banger, they don't have great power (though they arguably have more power than a 2.8 V6).

 

4 cyl gears will be

4 speed...3.55/3.73 with 3.55 being the most common

5 speed...3.73, 4.10, 4.56 with 4.10 being the most common... though some ended up with 3.55's (hardly any did)

auto...4.10, 4.56, with 4.56 being most common...though 4.88's are a very, very small possibility

 

 

a 4 cyl 5 speed with 4.10 gears will perform well as a d/d.

 

oh, and expect high RPM...but don't freak out about it. a 4 cyl's ideal power band is 2900-3300RPM. they're designed for it.

 

-Pat

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I've got a 91 2.5, which is MPFI. Until it started running funny, it did pretty ok on the 3.55 gears, it was pushing about 23 mpg. Now it's getting about 16 and runs like crap, still don't know why.

 

But as they said, a Renix Era 4.0 can get that or better mileage. Up until my recent motor swap(and it might back to this after I get the oil leaks fixed), my 88 XJ was getting 26 mpg.

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Thanks for all the great information. I don't think I'm scared of the 4 cyl. now. Another reason for looking at the 4cyl. truck is that it seems most of the 6 cyl. are automatics & I prefer a manual transmission for off road use. I keep finding 4 cyl. with manual trannys. :dunno:

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Strong little engine. If you are properly geared and using your Jeep as a daily driver or minimal offroad you will be fine. My dad used the hell out of the bed hauling various stuff, 4cyl handled it fine. I wouldn't expect to do any towing with it, nor would I expect it to perform on big tires/lift like a 6cyl will. My only real complaint about the 4cyl is the lack of aftermarket performance parts.

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Your right. & I do plan on lifting it. I'm going to have to hold out for a 6cyl. It just seems tough to find a manual transmission much less even finding one of these trucks. I've bought & sold a lot of cars over the years & I would have to say this is one of the toughest car/truck searches I have ever encountered. Very few.

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My search took about 6 months to find a 6cyl AX-15 at the right price. I didn't want the BA10. On one that I looked at the guy wanted 4k for an 89 with an old clutch, the BA10 that had a leaky output seal and rear main seal leak, and he said the reason for his pricing was because it had fresh paint. :nuts:

 

Hold out, you'll find one eventually and it will be worth the wait. :wavey:

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To me the 4 popper is almost the way to go cause of the price and availabilty. If you are worried aout the trans holding up, you can always swap in a stronger one, same goes for a MJ with a BA/10. I would almost rather swaps trans then do a motor swap. Also the 4 poppers lend themselves to v-8 swaps easier.. Less crap to pull out.

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See how truck drives over 55mph. When WE test drove my sons 2.5 I never went over 40 truck only had 65000 miles but 1 cyl had very low compression.To much vibration on highway because engine needs repair but I love it on city streets. Internal hydrolic clutch release bearing looses preasure all the time but I'm begining to think when engine vibrates it shakes fluid and this causes bubbles. If our trucks engine ran right it would be awsome love the 5spd,also truck is 2wd so less power is needed.

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There is some aftermarket support, but they are few and far between. Clifford performance make an intake and a header. Their intakes can be adapted to use a 4 bbl carb, 2 bbl carb, or their aftermarket fuel injection setup. A company called Accelerated motion makes a variety of cams for this motor. You can get roller rockers, port and polish the head, custome exhaust.... just depends on how much you want to spend. And if youd rather swap. buy this 4 cyl MJ now, and keep an eye out for a parts XJ with the trans you want and the 4.0 and swap everything over... maybe even late model one with the newer style front end. It all depends on what you want to do and what you are up for.

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No. BA 10/5 and AX-15 are both manual 5 speeds.

 

BA 10/5 is a crappy Peugot transmission used behind the 4.0 from 87-mid 89

 

AX-15 is a much stronger transmission used behind the 4.0 from mid 89-99.

 

AW-4 is the auto used behind the 4.0 AX-15 and AW-4 are both made by Aisin-Warner

 

Left : AX-15 Right : BA 10/5

oldnewunits9.jpg

 

AW-4

aw4_transmission.jpg

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buy this 4 cyl MJ now, and keep an eye out for a parts XJ with the trans you want and the 4.0 and swap everything over... maybe even late model one with the newer style front end. It all depends on what you want to do and what you are up for.

I was just thinking this

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