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So my 89 4.0 has 222111 on the clock, it had a rebuild somewhere ,at least i think , unless someone just pulled the head and everything and resealed it . Either way it s running like crap actually its running really rich leaving a black ring around the exhaust tip. Im fed up with it its been goin on for three months or so . Ive asked for help on here before and nothin really helped . so im gonna start freshwhat should i check , clean , or replace???

the whole jeep

EDIT i just did got a 96 for a grand needs a little work runs great and its stock so i can do what ever i want to it YAY 89 is for sale

If you haven't replaced the O2 sensor recently I would do that first. After that I would start looking at MAP sensor and a few other things. Sorry I can't help more but I don't know much about the RENIX engine.

I have an 89 cherokee that had the exact same problem... turned out in this case the map sensor was not correctly connected. it needs to be hooked to the vacuum port on the side of the throttle body that has very little (or no) vacuum when idling and increases as you accelerate. if correctly connected, change map sensor. Mine was so bad that I left a black cloud whenever I would hit it hard and gas mileage was about 10 or less.

I have an 88 that runs almost great, but no matter what I do, I just can NOT get her dialed in to run great. As far as I know, all sensors are original, so starting with the O2 sensor, I'm going to systematically replace all the sensors in the truck. The Renix is pretty sensitive to voltages, which makes them a little tricky because they were not wired all that well. redo all your grounds before replacing your sensors.