Hi I'm new to the forums and this is also my first time owning a jeep, I'm hoping that I can find someone who can tell me what's going on with my jeep or has had one that has done what mine is doing. It's a 92 frame with a 93 motor in it, the motor has 250,000 miles. Overall it's in good condition, hadn't been mudded or anything like that. When the original motor in the 92 went bad I had the 93 installed and it ran great previous to swapping, but now it's got a miss to it, it's hard to actually explain but you can start it one day and it will run like a dream, then the next day it acts like it dies for a split second non stop while going down the road. And the faster You drive the worst it will get I mean it will feel like the whole thing is trying to lock up, but it will stay running. I've replaced the dist cap and bug, fuel filter, fuel pump, had the gas tank checked for blockage, New transmission filter and oil, New air and oil filters. I've stuck a lot of money into this thing already and I've took it to several mechanics who tell me they just don't know what's wrong because they can't hook it up to a machine. Please if anyone knows what it might be let me know because I'm at a loss.

 

If it runs bad only sometimes you should pay attention to the factors. Like outside temperature for instance, weather, what kind of inclination you're on. Etc. once you see a reoccurring theme when it runs bad, that'll get you a lead.

 

First off welcome to the forum! Also.. Do you have an XJ or a ZJ? The ZJ wasn't made til 93. It sounds to me like you may have either a failing fuel pressure regulator, or a heat soak issue on the fuel rail. Do you have or able to get a fuel pressure tester?

 

It's a jeep Cherokee Laredo 92 body with 93 motor. I have noticed that it runs worse than usual on high humidity days or when it rains. It also runs bad going up inclines it seems.

 

Sounds to me like a possible weak fuel pump. Test fuel pressure at the rail. Fuel pressure should be around 31-35 on the 4.0L

 

One thing that leads me to this is the high humidity aspect of the problem. How are the spark plug wires? Are they dried out and brittle?