Run Rough w/ Black Exhaust Discharge

Lately, my 97XJ 4.0L has been running a little rough. I noticed that when I give it some gas you can see some kind of black substance come from the tailpipe and onto the ground. It kind of spatters out. The substance is a little liquidy. Looks sort of like what burned mud or carbon might look like. Has any one experienced this before. I replaced the O2 sensors last year when this problem had occurred. I ended up cleaning the plugs on the computer, and it ran good. But why would this happen? Some sensor go haywire? What do you guys think?

:wstupid:

carbon in the exhaust mixed with condensation-- it's wet, but the carbon almost seems to be floating in the water.. yes?

classic signs of faulty ignition or injector leaking into cylinder. I would perform a complete tune up and run a leakdown test on the fuel system. Look closely at the plugs you remove and if one or two are really black, you've found the injector/s that can be the problem...

post back with results and if no problems there, we can look into other things that can over-richen the mixture (MAP, IAC, O2, CTS, ACT, etc...) but until you know the state of tune is up to snuff, you may be trying to herd cats!

--Shorty

Shorty said:

you may be trying to herd cats!

--Shorty

Click to expand...

That's great!!

Well.....I put on new plugs, wires, distributor cap, and rotor. I noticed that all of the plugs looked fine, just used, except one. The plug from the number 4 cylinder had some debri that bridged the gap on the plug. So far so good, but it only acts up with that carbon-like tailpipe discharge after a while. Before this tune-up I would unplug the computer, clean the connector plugs, put it back together, and then it would be fine again for a while. Hopefully this tune up does the trick. If not, I probably would be looking into sensors or first, the injector in #4. Thanks for the help. I will keep you guys posted.
hasta