I have been trying to figure it out for about a year now on and off, Here is the story, Its the 2.5L
I bought the jeep for $150 because it had been sitting for about two years prior to my purchased, the reason it was parked was because it would not start, I figured I can fix it, great deal. Two flat tires too shouldn't be hard.
So... I first replaced the plugs and wires, rotor button and cap, didn't start. Replaced the ICM and it started...Yes I thought I did it....but...it was sputtering and blowing black smoke out exhaust, running rich, so I started replacing sensors, Map, O2 Sensor, CTS, Injector and CPS also the intake gasket..not in that order and not at all the same time. still ran horrible. So I did a compression check and found low compression in #1 and #2 cylinder. I pulled the head and found holes in the side of those pistons, I ordered pistons and ring set, when I pulled the pistons to replace the rings on #3 I found the groove where the compression ring was widened so I replaced #3 piston along with 1&2 also replaced rings on #4. Now I have good compression on all four cylinders. Replaced Head gasket and assembled tested and it still ran rich, then water pump went out so I replaced it. I replaced the fuel pressure reg but the new one ripped with the original spring that in the presser regulator so I put my old one back in with the smaller spring and it ran better but still rich, I tried to test fuel pressure but the gauge reads 0. and it is still running so I wasn't worried about it cause it ran better. It doesn't sputter or bog down when I drive it but there is definitely black smoke out exhaust and smell of richness. I also checked vacuum lines.. I replaced the four going into the TB and Map sensor and some others. Sprayed cleaner around hoses and no change, Did a vacuum test and I have about 11 or 12 Hg on the gauge. I can also unplug any sensor and it stills runs the same.
I was wondering what else could be wrong and could mechanical parts be causing this problem? I did read this very informative page that did help a lot I have checked everything mention on this page http://www.4wdmechanix.com/Tuning-and-Troubleshooting-the-2.5L-Jeep-TBI-Four.html
There might be some things I missed so if there is any questions please ask. I am thinking there could be lots more wrong with it and I am getting tired of it not getting any better. I just am going crazy trying to fix it.
Oh I also checked the Cat converter and it is not plugged.