Hello fellow XJers i am having a problem with my 94 XJ 4.0 5-speed. When the engine is at operating temp. it cuts out real bad under a load, if you just ease into it on flat ground it does ok but if i try to climb a hill or anything for that matter it starts cutting out, bucking and jumping and to clarify its not a miss and the CEL is not on. Things i have checked or replaced is:
Checked, fuel perssure is 31 with vacume line and 39 without and it stays spot on even while it is acting up, taken all connector apart and cleaned them with elect. cleaner, and checked and cleaned all grounds and yes it has plenty of gas lol.
Replaced, fuel filter, plugs, gapped at 35, wires, bug, cap, coil, coil pickup or cam PS, CPS, temp sensor the one on the t-stat housing and the one to the guage, TPS,
Oh and it seems like when its actin up the tach aint readin right. Any Help would be greatly appreciated, thanks in advance

 

Did you check compression on all six cylinders?

 

No i havent done that it seems like it runs too good otherwise its like somebody is flipping a switch on and off kinda like running out of fuel or like its vapor locking but i cant see a fuel injected vehicle doing that i will check the compression on it this weekend just to rule it out hopefully lol

 

I had a buddy's do this a few months back on some trails... seemed when the motor warmed up, it was vapor locking through the fuel rail. Took us all day and many frustrations to figure that out.... we poured cold water on the fuel rail when it happened last, and it cooled off enough to run right again.... now this was a venting issue due to slow crawling off road and the hot air not being able to escape.... but the 4.0L fuel rails are known for vapor locking like that under a load... He fixed his with luevers in the hood, some larger injectors and a bottle of dry gas...LMAO.... not sure if that helps any. how many miles are on this motor?

 

its got 135xxx miles on it, i was thinking about getting some of that reflective heat sheilding stuff and wrapping it around the rail and the line feeding the rail. do u think it could be that even with proper fuel pressures? and i was thinkin about raising the rear of the hood to release some heat

 

Allowing the motor to breathe and cool off is never a bad idea. And yeah, the pressure can check fine, but the problem could be intermitent. Installing a heat sheild is a great idea, and even if this is not your problem, one that I would still reccomend.

 

*Test your MAP sensor. And be sure that the vacuum line leading to that sensor is pulling good vacuum. Directly involved with fuel/air ratio

*Consider replacing your oxygen sensor. They have a finite lifespan of between 100k and 150k, depending on energy efficiency. And they can fail before they set a check engine light.

 

I had this same problem awhile back. it was the internal regulator in the alternator shorting out when the alternator started charging.

 

ran across this once. high speed miss going uphill. bad distributor.

 

Had this problem once. It was a clogged catalytic converter. If your exaudt isnt welded together, disconnect the downpipe from the cat and see if it runs right. At the very least, the sound will anger the elderly, which is a bonus...

 

Ok so i wrapped the fuel rail with reflective heat shield replaced the distributor with no luck. I havent checked the o2 sensor or the tps would they make it cut out, or is there any other suggestions? im lost i have also noticed that my tach dont seem that it reads right all the time, could it be in the ignition switch or is there a sensor i dont know about on HO's, im used to renix, this is very frustrating thanks

 

and to A JEEPR could u tell me a little more about what urs was doin or how to test to see if that is my problem before i go out and buy an alternator, Thanks!

 

did you ever check for codes even thought lights not on

 

RIGHT!!!! There could be some "pending" DTC'S, that are enough to cause drive-ability issues, but sometimes won't throw a code..

 

i know you replaced the cps. but maybe you got a bad replacement.