Running fairly rich

Hey ya'll. Since I've got my XJ its been running fairly rich. The exhaust is coated with black gunk and when its running it splurts out the black gunk. So I do I go about making it run cleaner? :repair:

Black gunk??

I'm guessing this is a 98 4.0L.

Test your oxygen sensor. If it's reading lean, that's a good clue that either it's bad, or getting a false reading. Exhaust leaks before the O2 sensor can fool it, use a piece of hose as a stethoscope to search for one. If there's no leaks, probably the O2 sensor is bad. Could also be an O2 sensor wiring problem.

If the O2 sensor is in fact reading rich then it's probably OK, or at least not the cause of the problem (it might be destroyed by the black gunk). You also need to check the map sensor and throttle body position sensor. Or it could be an intake air leak although that usually causes high idle. Or leaky or stuck fuel injectors.

When was the last time you did plugs/cap/rotor/air filter?

Could be a bad Cat.

This is ModTech,you would get better/more responses from OEM Tech.

Coolant sensor, MAP, o2 sensor, exhaust leak upstream of o2 sensor, bad synch sensor in the distributor, lack of proper maintenance--cap/rotor/plugs/wires/air filter, all those things can lead to issues. Intake leaks will usually result in a leaner mixture in the cylinders giving a higher idle speed.