Diagnosing an issue with my 1986 XJ 2.8L

Trying to figure out an issue my XJ is having, aside from it being a 2.8L.

1986 2.8L V6 3-speed Automatic
Sympton - drives shifts, but when I hit 40mph it jerks and won't continue acclerating. I can drive around all day under 40mph without issue. 4wd drive still works without issue, though I haven't pushed it up to 40mph.
Its a rather violent jerk as well.
Can feel all the shifts as you acclerate too.
No issue at the idle, or just rev-ing the engine in neutral.

Current modifications to it:
EMPI 2bar Carb from Quadratec
Rough Country 4.5" Suspension Lift.
The Carb and lift have been on for a few months before this happened.

Any ideas would be appreciated,
Also if it is the torgue convertor or the transmission (those are the general consensus of a few friends that have offered their opinions), where do I find replacements ones and how expensive am I looking at?

Thanks for any advice.

Fuel Pump? Once they start to go, any load at higher RPM will cause stutters....

That or it's the infamous POS GM 2.8L V6 problems revealing themselves....

poorboy_616 said:

Fuel Pump? Once they start to go, any load at higher RPM will cause stutters....

That or it's the infamous POS GM 2.8L V6 problems revealing themselves....

Click to expand...

Wouldn't it be an issue while just rev-ing the engine while parked/in neutral?

While revving an engine in the driveway does use fuel, it doesn't use nearly as much fuel as when the engine is under load. It sounds to me like a fuel starvation issue, but could possibly be timing related, as well. Have you checked the timing, as well as the total advance? The timing would have to be WAY out to produce the symptoms you're describing, but it's not out of the question.

Check for clogged fuel filters (even if the one you have is fairly new, it could still be clogged). If the fuel pump is old, a replacement isn't that expensive and will eliminate that from the list of possibilities, and check for kinked fuel lines, too. I hate to break it to you, but EMPI ain't what they used to be, so that could very well be the problem, too.

Try these & report back.....
:wave:

I have the same vehicle and mine was the feul pump but it was'nt going out it was falling off the 2 mounting bolts were backing off and when i got to higher speeds it would jerk you around I didnt know what was going on until it all but fell off 1 bolt fell out and the other was held on by a couple of threds luckly i caught it before i lost the rod.

Ive been contemplating getting that EMPI carb also is there a noticable gain in performance and feul economy.

Fuel Filter is new. The old carb had it in it, so had to put an aftermarket inline one. Old carb was causing Vapor lock issues inside the filter area.

So check the motor mounts and possibly do the fuel pump next.
Alright will check the mounts today, if bad will replace. Else try the pump next.
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The EMPI Carb http://www.quadratec.com/products/51318_107.htm corrected the following issue for me, my old carb was having Vapor Lock anytime I drove it over an hour, it was occuring right in the fuel filter that was in the Carb.
I did have to buy an inline fuel filter for it, and one of my racing friends helped me with that, ended up getting one of those glass ones you can see through to check it (main reason I know it's not clogged).
Far as performance:
I never really cared about the fuel mileage in it. As I use it on Mud and Rock and it isn't a daily driver. I did however notice there was a marked improvement in usage, where it would be 1/2 to 3/4 round trip for a few places I go, I noticed it was about only a 1/2 a tank now.
It did improve horsepower somewhat in 'response' department. Wasn't a huge increase, but was a noticeable one.
Honestly if it hadn't been for the Carb having other issues, I probably would have never made the mod.
One bad thing about the Carb we found was after installation the screw post and the bracket over the intake were too big for the stock air assembly and stock hood.
we slightly moded the stock air cleaner lid to fit that, and had to cutting wheel off the extra part of the post.

Hopefully it is just the motor mounts, I'll upgrade them to some of the Brown Dog ones. If he makes them for a 2.8L, on his list I only see the 2.5L and the 4.0L for the Cherokees. I know I like the ones that I got from him on the YJ's 4.0L.

get some polyurethane control arm bushings and make your own mounts. crown is the only company that make stock replacements and they suck balls they will tare every time you get on it. so if you drive like a grandma then use stock.

LOL if I were that good at fab-ing I would be building a buggy.

I have to take a couple of measurements tonight for Brown Dog to verify the right one for me. Their site had the wrong listing on their homepage.