Is 4 cylinder really that bad?

[5-90]

I'm willing to bet that the versions run something like...

Renault 2.1L Diesel/Turbo Diesel
2.46L AMC
2.5 GM "Iron Duke" (used only in CJ/YJ, IIRC)
2.5L ChryCo I4 (Later Jeeps, after Daimler-Benz purchase, likely)

That's four right there. I do seem to recall the Iron Duke being used with CJ's and maybe some early YJ's, but I can't swear to it all...

Given a choice, I'd have a hard time picking between the GM2.5 and the AMC2.5, as the GM2.5 is nearly legendary for endurance, but I think the AMC is a little better for low-end power...

5-90

 

[Eagle]

I'm willing to bet that the versions run something like...

Renault 2.1L Diesel/Turbo Diesel
2.46L AMC
2.5 GM "Iron Duke" (used only in CJ/YJ, IIRC)
2.5L ChryCo I4 (Later Jeeps, after Daimler-Benz purchase, likely)

That's four right there. I do seem to recall the Iron Duke being used with CJ's and maybe some early YJ's, but I can't swear to it all...

The Renault diesel doesn't count. We're talking about the 2.5L gasoline 4-banger here.

The GM "Iron Duke" was used in Eagles and CJs, but was never used in the XJ. The AMC 2.5L was introduced in the XJ. The same basic engine was used right through to the end. The differences were in fuel delivery and ignition.

I previously posted that there were three versions:

Remember that there were three generations of the 4-cyl in the XJ:

Gen 1 (1984 - 1985) = carburetor

Gen 2 (1986 - 1990) = throttle body injection

Gen 3 (1991 - 2000) = multi-port injection

I'm willing to accept Ghost's correction. make it four -- 91 thru 96, and 97 thru 2000. Not sure about the newest TJ engine. I don't know if that's "our" engine or a new engine of DaimlerChrysler design.

FWIW, the TBI version used essentially thesame Renix ignition and injection control as the '87 thru '90 4.0L I-6. In fact, they share the same CPS.

Also, aftermarket replacement pistons for the 2.5L are the same slugs as for the 4.0L. The 2.5L is just a shortened version of the 4.0L (or, since the 2.5L came first, perhaps it's more accurate to say that the 2.5L is a shortened version of the Jeep 4.2L, and the 4.0L in turn is a lengthened version of the 2.5L.)

 

[MudDawg]

From my research the 2.5 was designed by Renault to be built mostly with the tooling that AMC had..as Eagle says the 4.0 is a "stretched" 2.5 basically...they share pistons, valves, connectings rods,etc...the block deck height on the 4.0 is higher to allow for the longer stroke of the 4.0 crank..

Interesting note..if you build a stout 2.5 including valvetrain mods and are concerned by the strenght of the whimpy single row timing chain...a Mopar Performance double row chain/gearset for the 4.0 will fit the 2.5...just remove and discard the stock chain tensioner and slipper. add a 4.0 cambolt pin kit to control any possible "cam walk".

 

[5-90]

So then, ChryCo never got round to putting their own little 2.5 into the XJ? That's good news, I never did like that mill. Don't know why, I was just never pleased with it...

Trivia point - isn't the 2.46 about the only 4-cylinder engine that AMC used? Just wondering...

5-90

 

[Dr. Dyno]

The AMC 2.5 4-banger that was used in '84-'97 Jeeps is a very strong and reliable engine, even if it is a bit underpowered. The legendary 4.0 is basically the same engine with two extra cylinders and a longer stroke.
The carbed and TBI'd 2.5's are the most underpowered and converting them to MPI is a good upgrade. The 2.5 does respond well to performance upgrades and here's a few:

2.5 I4 (Factory ratings 120hp@5400rpm/140lbft@3500rpm)

1. Homebrew FIPK with 5" Powerstack cone filter
2. 4.0 TB with taper bored to 60mm
3. Poweraid TB spacer bored to 60mm
4. Intake manifold heatshield
5. Flowmaster 50 series 2.25" muffler
6. High-flow 2.25" cat
7. Clifford Performance header with 2.25" piping
8. Champion copper plugs
9. Magnecor 8.5mm plug wires
10. Electric fan conversion
11. Relocate IAT sensor to FIPK heatshield

With the package of mods listed above, output should improve by 20% to about 145hp.

 

[5-90]

SIDEBAR - Hey Doc - you get my email on Renix ECU data streams? Email or PM if you have questions or want to know why...

5-90

 

[Mikel]

A friend of mine has a 86 XJ with the 2.5L, and IMO it has adequate power for most driving. The amazing thing is that this engine has 200K miles and my friend has probably changed the oil every 20K miles... If the jeep got lucky. I think what my friend did was to drain the old oil, run it through an old sock and put it back in the engine. And somehow the thing still runs!
That ALONE has made me a believer in the 2.5L.

 

[jeeperzcreeperz]

11. Relocate IAT sensor to FIPK heatshield

What is that???

 

[old_man]

I loved my 2.5L. I built it up a bit, but pulling long hard mountain passes sucked. Never had a need for more power on the trail

 

[87manche]

So then, ChryCo never got round to putting their own little 2.5 into the XJ? That's good news, I never did like that mill. Don't know why, I was just never pleased with it...

Trivia point - isn't the 2.46 about the only 4-cylinder engine that AMC used? Just wondering...

5-90

I had one of those in a 90 sundance with a 3 speed tranny. Worked itself to death at highway RPMs. Was real strong, torquey. Leaked oil faster than I could pour it in though. Had a habit of warping valvecovers, then leakin oil onto the exhauast manifold. Once put out an engine fire with a Biggie Coke....I hated that motor too.

 

[kendrick]

In my opinion the four banger has enough power for most things but the 4.0 I6 is bullet proof. I've had a couple friend have problems with fours (I'm not saying we didn't abuse them) that needed rebuilds. I recently sold one of my xj's which was a 86 4.0 with 185,000 miles on it. The only thing ever done to it were oil changes and it burned no oil. Occasional oil changes and these power plants would seem to be industructible. My current one only has 80,000 0n it but so far so good. I usually don't get caught up in brand wars but I swear by the Jeep 4.0.
-Kendrick

 

[5-90]

11. Relocate IAT sensor to FIPK heatshield

What is that???

IAT = Intake Air Temperature (sensor.)

Essentially, they're saying to take the IAT out of the manifold (or the "active" one, if you'd prefer not to replace it with a plug) and move it farther "upstream" in the intake and away from exhaust heat. This will result in a lower temperature reading, interpreted as a slightly higher intake air density.

This, in turn, would mean more fuel into the engine, and therefore more power - IF the higher density (more oxygen) reading shown by the relocated IAT is borne out with intake volume. I'm not sure myself - haven't tried it yet. I think Dr. Dyno has, or someone else whose opinion I actually respect - and you might want to see what he/they think.

5-90

 

[uvaldetxj]

Sorry to hijack, but i've got to share the good news.
So far i've read that the 1986 2.5L is Throttle Body Injected.

This is good news to me. An uncle of mine has an old MJ with the 2.5. He likes the truck, and hasn't agreed to sell it to me, but no one else in our family is quite into XJs/MJs as much as I am.

Sounds like i've got some MJ hunting to do.

 

[Jeffro600]

4 Cylinders are perfectly fine as long as you dont mind gearing it to the moon and reving the snot out of it at highway speeds...take them offroad and they dont give up much to the larger motors. I had an older toyota truck that had a 22R(not the most powerful 4 cylinder out there!!) and it had 33's. Had 5.29(or was it 5.71??) gears in it and it screamed bloody murder on the highway at 70+, but it did fantastic offroad. Gearing is the make or break for a 4 cylinder...and despite the small displacement, dont expect more mileage. I was lucky if i saw 14-15 MPG highway.

 

[RichP]

We've got 2 TJ's and a YJ, all are 2.5 4 bangers with 5 speeds, running 30's it's pretty good in my daughters, the sons TJ with 33's leaves a bit to be desired on the hiway, the 93 YJ with 225's and 5 speed is a little rocket and the factory D44 with locker makes it a pretty good jeep. Too bad the previous owner butchered the radio mounting area, got some work to do there...

 

[devildog0]

The 03 Tjs are packing a 2.4 L enigne out fo Neons. Soppousedly more powerful than the 2.5. I would like to see one swaped in place of a 2.5 if the claims are true.

 

[devildog0]

My parents have a 2.5 L 2wd XJ I love that little thing runs like no tommorrow. Infact I'm keeping an eye out for a TJ or an XJ for real cheap with the 2.5

 

[Ron Hyslop]

My 86 TBI is going strong at 200,000mi. Wish I could find a late model one.

 

[Dookie]

i'm not reading all that. but the four-banger sucks balls compared to the 4.0. i'd never, ever, ever buy another one...

 

[MudDawg]

I was hoping to be able to put up some video of a 2.5 in action...but the tape ended up on the cutting floor and didn't make it into the trucks gone wild 2 dvd...There are only two fleeting shots, but neither in action. Oh well there are more chances...they are taping again tomorrow.