Jeep Wrangler Forum

Jeep Wrangler Forum (
-   YJ Tech Forum (
-   -   2.5 engine questions from a Jeep newbie (

Dan95 04-23-2013 08:16 PM

2.5 engine questions from a Jeep newbie
Hello everyone, I'm new to Jeeps & thus new to the forum. At 50 years old I have seen the light & drank the koolaid, I'm now a Jeep cult member :wavey:

I'm not new to wrenching & rebuilding engines, now my roots run deep on big & small block Chevys. With that said I want to learn everything there is to learn about my little 2.5 - 4 banger. I don't mind the fact that it's malnourished in the power department, my sand drags & mud boggin days are behind me as I should be saving money for retirement verses spending money on blown transmissions & rear axles, did it done it, have the T-shirt :)

Is this little 2.5 worth rebuilding ? Were they a decent engine ? Did they make a pre- emission version with a carb that I could throw in here ? I'm an ole chevy guy where you could bolt everything from an inline 6 to a small block to a big block to the same transmission bell housing. I'm at the age where a sputter is caused from sticking points & hesitation was caused by the carbs vacuum secondaries not pumping enough fuel at full throttle. I'm not a fan of a computer screwing up my engine because I left my gas cap lose (ya, I know, I'm an ole fart)

Is this a Jeep or Chrysler engine ? Is it a time proven, rebuildable engine or is it a throw away engine ? I want to learn everything I can about this little 2.5 in my Jeep so I can make decisions on how to proceed in the future as it has 150,000 miles on it.

All opinions / Advice is appreciated,

roadsterbob 04-23-2013 08:28 PM

2.5 engine
The 2.5 is a 4.0 minus two cylinders. They seem to be a good engine and are pretty bullet proof if you don't get too crazy with them. Mine has 174K on it and it does have a few strange rattles. It doesn't really use any oil and only drips a little from the rear main. I am certainly going to rebuild it whenever the time comes!
Mine is a '94 and although I am an old carb and points type of guy, I do like the fuel injection and electronic ingnition...

Dan95 04-23-2013 08:59 PM

That's good to hear that it is basically a shortened 4.0, I have heard good things about the inline 6, I have heard nothing about the 4.

I agree that when fuel injection & electronic ignition is working it's the best compared to a carb & points, but when the computer decides to do crazy things it can be a nightmare for an old school mechanic like me to diagnose.


Defcon 1 04-23-2013 09:26 PM

The 2.5 AMC 150 is a boss. I have 210K on mine and it doesn't burn a drop of oil. There are some guys on here that have 250K+ on their 4-Cylinders, so at 150K you haven't even broken it in yet lol. Take care of that little engine and it will serve you well. I change my oil every 3000 miles, no exceptions. Just don't do anything crazy to it like make it turn over 36" Swampers and you'll be good to go lol.

Yes, the old 2.5's were carbureted, however as you know with carbs if the Previous Owners didn't keep them tuned correctly it usually winds up being a can-of-worms for the new owner. As for the electrical controlled 4-Cylinders, well, I'd call them a "simple-electronic controlled" engine. There's really not a whole lot to it, not compared to todays computer controlled engines at least. A couple of sensors here and there, and you just change the one for the code that the computer gives you.

All 2.5's (even 4.0's) usually develop a lifter-tick at the 160K mark, so don't get too worried when that happens lol. Other than that they're usually really trustworthy and easy to troubleshoot. A Chilton or Haynes manual can tell you a bunch of good technical stuff about it, including the fault codes, (of which I believe there are only a couple dozen).

A lot of guys, (mostly everyone), find the 2.5's only real drawback is the power-output. I don't think I've heard of anyone complain about it harshly because of it's longevity, usually people swap them out because they want more power, not because the 2.5 blew up on them prematurely. It's a good canidate for a rebuild, just keep an eye on it and perform good routine maintenance and it'll last.

gunslinger24 04-24-2013 08:14 AM

I like my 2.5. Burns clean, runs good and has not let me down. As crazy as it sounds, I have passed my friends 4.0 on a slight incline on the freeway. I was thinking about swapping in a 4.0, but I think I'm just going to build a 180-200 horse 2.5

jeff_in_rc 04-24-2013 09:24 AM

I have had my 2.5 YJ for a little over a year now and like others it has never let me down. It might be down on power compared to the 6's but it has worked well for me. I got it with 103,xxx on the clock and it now has 112,xxx on it and it runs great, gets decent mileage for a brick with wheels, does not burn nor drip oil. Take care of it and don't rev it to the moon and you will be surprised.

Dan95 04-24-2013 05:14 PM

Thanks for the good reviews on the little 2.5 ! You made my day reading this as I can live with the low power, I drove a 4 cylinder S10 for the last 10 years so I'm used to low power & I know my jeep won't get stuck in 6 inches of snow like the S10 did.

The jeep was well taken care of, the previous owner used Mobil 1 oil every 3,000 miles, I was handed the pile of receipts when I bought it. I guess I don't have to worry about a rebuild in the near future :)

jeff_in_rc 04-24-2013 05:35 PM

So how about some pics?

Jeepfreak94 04-24-2013 05:43 PM

Had my 2.5 for 18 years. Changed oil every 5k with synthetic oil and still has 50 psi oil pressure and the compression tests within 5 psi of optimum. Swapped gearing over to 4.88:1 a few years ago. Made a HUGE difference in drivability with my 32's. I can wheel a whole weekend on a single tank of fuel with plenty left over. The 4.0 Jeeps can't do that. Just a 'mean buzzin' 1/3 dozen!'.

Dan95 04-24-2013 10:04 PM


Originally Posted by jeff_in_rc (Post 3678312)
So how about some pics?

jeff_in_rc 04-25-2013 09:10 AM

Nice Dan95, very nice. Thanks.

Xpress 04-25-2013 09:19 AM

I assume this is a 1995 then.

If that is the case, then you have the MPFI version of the 2.5L engine. They made 2 versions of the 2.5L:

1987-1990 is TBI (Throttle Body Injection)

1991-1995 is MPFI (Multi-Port Fuel Injection)

The power difference between the 2 is negligible, but they do have enough power to get the Jeep up and moving. Mine was my DD for years until my engine took a dump on me. Someone along the line of previous owners didn't take care of it. Mine did the highway speed limit no problem.

As far as converting to carb, doubt it's possible. The distributor is electronic, you'd have to overhaul the entire engines electrical components to get that to work. Keep it MPFI if you want as little hassles as possible, and as much power as possible. And as always, if you get stuck with an issue, post here and we can all try to help as best as possible.

Also, keep in mind, entirely for legality reasons around here, Federal law prohibits you from removing any and all Federally mandated emissions equipment from the Jeep. That means you can't talk about removing specific components vital to reducing emissions output ;)

Jeepfreak94 04-25-2013 10:32 AM

Do all your basic maint., including a quality tuneup. Swap on a 4.0 throttle body and a set of Neon/Stratus injectors( use the search function for full info) then put a 2 1/4" exhaust with a better flowing muffler and enjoy. It is a great engine and under appreciated,in my opinion.

wrangleryj90 04-25-2013 12:37 PM

I love my 2.5l I have no power problem it does awesome off road and on road I don't hardly drive on the freeway other then to camping spots or to go wheeling

Dan95 04-25-2013 09:35 PM

Thanks for all the good replies everyone, I will check out the injectors & exhaust recommendations.

As far as emissions, how do people get away with installing small block Chevys then ? They are running around all over the place around here ? (mid Michigan) we do not have emission testing, I always heard rumor that after 10 years emission standards did not need to be met ? I realize that could be a very different law for each state & I must admit that was a long time ago I heard that rumor.

This little power plant has enough power for me, my days of installing 18 - 44 ground hawg tires were almost 30 years ago. Now if I can get to work in Michigan winters that will probably be the extent of my 4 wheel drive adventures.


Xpress 04-26-2013 10:14 AM


Originally Posted by Dan95 (Post 3683737)
As far as emissions, how do people get away with installing small block Chevys then ? They are running around all over the place around here ? (mid Michigan) we do not have emission testing, I always heard rumor that after 10 years emission standards did not need to be met ? I realize that could be a very different law for each state & I must admit that was a long time ago I heard that rumor.

The legal way is to transplant all of the emissions equipment out of the vehicle the engine was originally in. Said engine also has to come out of the same model year or newer vehicle (so for my 1989 YJ I have to use an engine that was manufactured in 1989 or newer). Then you proceed to having a SMOG Referee evaluate the engine swap to verify the validity of the swap, then he/she will run it on the dyno and approve or disapprove it depending on whether or not it passes.

From there, they will swap the engine code onto your vehicle title and from then on your engine swap is absolutely legal.

There are states that don't bother with inspections or emissions testing and that's how people get away with doing whatever they want. Though legally, they are not allowed to. If an officer sees fit to inspect the vehicle, he or she can likely impound it and fine you for breaking Federal law, and then you are in trouble. You will have to get such a swap legalized.


The 2.5L is a great engine, pretty bulletproof, and it goes anywhere you want it to. Has more than enough power. Those who knock it are just used to something that can haul 10,000 lbs at 65mph up a 7% grade. It slows down a little on its own, but it'll motor along just fine.

All times are GMT -5. The time now is 03:57 PM.

User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.