Why Are The 2.8's So Bad?

[comanche1989]

First off, I know they are low on power and may be less efficient, but what makes the engine so bad? They may not be the perfect engines for the Comanches, but I've seen many vehicles with those older 2.8's with over 200,000 miles! I don't mean to ruffle anyone's feathers, I'm just curious why they are so hated.

[GirsMJ86]

I would say it is because of that lack of power. They only netted you something like 7 more hp but had less torque than the inline 4. The one I had accelerated slower than my moms current yaris. I would not want one in a rig I would be planning on off roading with and it wasn't much fun on the highway.

 

Just because there are a lot of them out there doesn't make them any better. Most people just don't care enough to swap drive trains or just live with it because the car was cheap and they just want to get from A to B. Any engine can get over 200k with normal maintenance.

[mpace6a]

All of the vacuum, and the carb and emissions crap make them unreliable. Plus there was a casting problem and they have poor low end oil circulation, causing burnt up bearings and thrown rods. Better design later on with the tbi intake and better castings, but still low powered and ineffecient. Though not entirely bad if you have a lead foot. Cuts down on my speeding big time. In hindsight,I would NEVER put one in anything because they really don't have anything good about them. No power, no torque, and ineffecient.

[onlyinajeep726]

All of the vacuum, and the carb and emissions crap make them unreliable. Plus there was a casting problem and they have poor low end oil circulation, causing burnt up bearings and thrown rods. Better design later on with the tbi intake and better castings, but still low powered and ineffecient. Though not entirely bad if you have a lead foot. Cuts down on my speeding big time. In hindsight,I would NEVER put one in anything because they really don't have anything good about them. No power, no torque, and ineffecient.

 

x2

[jimoshel]

:agree: That too! Just pulled a 2.8 from my '86. Got a hole in the pan where no 2 rod went thru it. Can not believe the crap I was pulling from that engine. Enough vacuum lines to outfit a Navy cruiser.

[gogmorgo]

Even in GM circles, no one really cares much for them. For pretty much the above reasons. Usually you hear about poor oil circulation due to tiny and/or plugged pickups, and gasket (all of them) failures. They also don't respond very well to neglect. Mostly, though, it made all the power of a 4cyl with the fuel economy of a V8. :doh:

That said, the 2.8 went into just about everything GM built in some configuration or other, and sold it to a couple other manufactures, so there's a colossal number of them out there. Even if a relatively small percentage of them had issues, that number got blown out of proportion. There's a bunch of them that had issues, but there's still a pile of them out there doing pretty darn good with high mileage.

As with all things, people make the most noise when they're complaining, and no one complains when things work. There's no reason to be scared of them because they're unreliable. By no means are they ticking time bombs. They'll do pretty well if you keep up with regular maintenance. Just be something less than surprised if something does go wrong

 

My Dad's Impala with the 3.4 (based on the 2.8, and you hear lots of complaints identical to 2.8 complaints) was an ex-rental. He had no engine problems whatsoever, ran the cheapest oil and gas, didn't always keep up with oil change or other maintenance intervals, and it was still running like the day he bought it when my sister wrote it off early this year with 240,000 miles on the clock.

[54bobby]

not to thread jack (but i will) what about my AMC 2.5? is it a decent engine or a piece of junk?

[GirsMJ86]

The 2.5L is a great little 4-banger IMO. It sure puts the 2.8L to shame. Good mileage and good power in a nice little package, and it kept getting better over the years.

[cruiser54]

not to thread jack (but i will) what about my AMC 2.5? is it a decent engine or a piece of junk?

Great little motor!!

[Garvin]

My brother had an '83 Chevy Celebrity that had the 2.8L and the thing ran like a champ, the trans on the other hand took a crap and it got scrapped because of that.  My '86 MJ had the 2.8L and it was nothing but troubles.  It was abused before I got it though and figured out it had a bent pushrod.  I replaced the pushrod just to have 2 more bend within the hour and I just ended up ripping it out and scrapping it in favor of the 350.  I've heard very little along the lines of complaints for the 2.5 but it just doesn't put out enough power for my liking (and I'm not really a fan of 4 cylinders), but that's all personal bias.

[CoryMJ89]

Bc it's a gm motor haha

[Eagle]

:agree: That too! Just pulled a 2.8 from my '86. Got a hole in the pan where no 2 rod went thru it. Can not believe the crap I was pulling from that engine. Enough vacuum lines to outfit a Navy cruiser.

 

^^^ This.

 

Back when these were the current offering in Cherokees and Comanches, a very good friend and racing buddy was the service manager at the dealership where I bought my '88 Cherokee. I stopped by often just to say hello. It was very rare NOT to find a 2.8L Cherokee with a rod or two sticking out the side of the block.

[GirsMJ86]

Bc it's a gm motor haha

 

Well now I don't know if I'd go that far, the 350 is an awesome motor and the 454 is even better. A family friends brother has an old J-Truck with a 454 swapped in and that thing is a beast, the 401 guys have nothing on it.  :laughin:

 

But in all seriousness, just look at this pic. All those vac lines... that is just uncalled for.

[dasbulliwagen]

The Jeep 4.0 was based off of the 2.5 and have a lot in common as far as dimensions are concerned, as well as some parts. My trucks original owner replaced the 2.5 at 140,000 miles because it was leaking oil. The current rebuuilt 2.5 in it had over 210,000 miles on it now and is still running great. Though I did buy a spare to keep around just in case. It does what I need it to do.

[Eagle]

Actually, the 4.0L was based off the 4.2L, and the 2.5L was the 4.2L with two cylinders removed. Yes, I know the 4.0L didn't come out until three years after the 2.5L. The engine family that ended with the 4.0L Jeep engine started in 1964 with the AMC 232 c.i.d. in-line six. A couple of years later they added a 199 c.i.d. version. In the mid-70s they stroked it some more and came out with the 258 (4.2L). That stayed with us until the early 90s in the Wrangler.

 

They are all the same basic block. The block has seven main bearings for six cylinders, which means every crank throw is fully supported. There is no flex in the crank, which is why the engines are basically indestructible. The 4.0L version is the first one where they reduced the stroke and enlarged the bore. ALL the other versions used the same pistons, with different cranks and different length connecting rods.

[CoryMJ89]

 

 

Bc it's a gm motor haha

Well now I don't know if I'd go that far, the 350 is an awesome motor and the 454 is even better. A family friends brother has an old J-Truck with a 454 swapped in and that thing is a beast, the 401 guys have nothing on it. :laughin:

 

But in all seriousness, just look at this pic. All those vac lines... that is just uncalled for

 

Okay true not all gm motors are bad I wanna see that I truck of ur that be sweet I'm currently working on mine 69 j2000 short we Buick 350 just love them old trucks(:

[glundblad]

I bought a Pontiac 6000 STE in 1986.  I believe it had a 2.8 with multiport fuel injection.  I remember it wasnt too terribly fast but I thought it could do pretty well compared to most other cars of the period.  I was pretty happy with it's performance.  Maybe the fuel injection made a difference?

[Comanche_Fanatic]

2.8L had bad design flaws (blame GM on this one) so theyre not as durable as the AMC motors. personally I'd only use it for highway at 70mph steady, other than that scrap it.

 

vacuum system is horrible on this motor, half of mine is missing, i don't even bother with it.

[onlyinajeep726]

 

Bc it's a gm motor haha

 

Well now I don't know if I'd go that far, the 350 is an awesome motor and the 454 is even better. A family friends brother has an old J-Truck with a 454 swapped in and that thing is a beast, the 401 guys have nothing on it.  :laughin:

 

But in all seriousness, just look at this pic. All those vac lines... that is just uncalled for.

 

 

Kill it!  Kill it with fire!! Quick!

 

That is a monstrosity of an engine with all those vacuum lines just dry-rotting away... eek.  :ack: 

[Tempus_Fugit]

It's not so much that the 2.8's are so bad. The fact that they are GM sourced turns off the hardcore jeepers for sure.

 

it more that the 2.5 and 4.0 are so good.

[Garvin]

It's not so much that it's a GM sourced engine, the main issue is it just doesn't put out enough power for the gearing that they matched to it.  A lot of the hardcore wheeling Jeepers turn to GM engines when building up a competition rig, usually closer in lines with the LQ or LS series.

[harris1986]

:agree: That too! Just pulled a 2.8 from my '86. Got a hole in the pan where no 2 rod went thru it. Can not believe the crap I was pulling from that engine. Enough vacuum lines to outfit a Navy cruiser.

Agree ^  No power at all, top end is 60, Praying the entire time that it don't blow up

[omega_rugal]

bad engine prone to many problems either alone or combined, low power...

 

the only good thing about this is engine is you can swap it for a 4.0 and then sell it as junk...

[Green Mesa XJ]

Well the 2.8 had a crap intake, combined with crap carburetor with restrictive exhaust and damn stupid emissions and miles of vacuum tubes. Compounding those problems was gm sold the worst of what they had on hand to AMC. 1985 gm upgraded the 2.8 cylinder heads, slightly more power stayed in use until the last 3.4 rwd in 1995. Also redesigned the block with rubber rear main seal and bigger oil journals better bearing size.

But the 1986 Jeep got 1985 blocks and 1984 cylinder heads. Maybe some got the newer mid-year block, but most I've seen had old number cylinder heads so didn't get the upgraded HP GM boasted about.

 

That's an awful lot to overcome out of the box.

If I look at a 86 with a 2.8 my minds already making a list of upgrades and parts to swap.

 

4.0 is a legendary engine hard to compare to that. Adding it to a 86 mj or XJ is doable but not simple.

 

All that said I don't absolutely hate the 2.8, I've got to have close to 300k on mine, it is under powered but never quit. Gotten through everything I put it through off road, sucked getting to speed on the highway, or going up a steep hill especially at high altitude, fine for city driving. Maybe because it has a 5 speed it's been more livable to me.

 

I would tell anyone starting out with a 2.8, if you plan on keeping it a 2.8 swap out the carburetor as a first step, if you plan on keeping the jeep you should probably upgrade the engine to a 3.4 as a start and do the fuel system upgrades.

 

 

 

 

 

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[Minuit]

The only good thing about a 2.8 Comanche is that you can readily swap a 3.4 into it, which STILL leaves you with an inferior engine to the 4.0. With that said, I've seen some 2.8 Jeeps with ridiculous amounts of miles on them. No idea how many engines it took to make it that far though.