98 JGC 4.0L IS RUNNING VERY RICH,NEW CHAMPION PLUGS PUT IN 1 WK AGO
ARE BLACK ALREADY AND ITS DRINKING GAS.I HAVE REPLACED THE IAC,PLUGS, WIRES DIST. CAP/ROTOR BUTTON AND CLEANED THE TROTTLE BODY BUT THE JEEP STILL MISSES BIG TIME.MY QUESTION IS CAN A POSSIBLE CRACK IN THE EXHAUST AND/OR INTAKE MANIFOLD CAUSE A MISS
IN THE ENGINE{BAD MISS} AND THE RUNNING EXTREMELY RICH ISSUE ,THE ENGINE LIGHT WAS NOT ON AND THERE WAS NO CODES STORED,LIGHT CAME ON ABOUT 1/2 HR AGO AFTER I CLEANED THE TROTTLE BODY.I AM THINKING O2 SENSOR,BUT DONT WHAT TO REPLACE IT IF THERE IS AN MANIFOLD ISSUE.ANY SUGGESTIONS,PLEASE HELP AND THANKS IN ADVANCE:banghead:

98 JGC 4.0L IS RUNNING VERY RICH,NEW CHAMPION PLUGS PUT IN 1 WK AGO
ARE BLACK ALREADY AND ITS DRINKING GAS.I HAVE REPLACED THE IAC,PLUGS, WIRES DIST. CAP/ROTOR BUTTON AND CLEANED THE TROTTLE BODY BUT THE JEEP STILL MISSES BIG TIME.MY QUESTION IS CAN A POSSIBLE CRACK IN THE EXHAUST AND/OR INTAKE MANIFOLD CAUSE A MISS
IN THE ENGINE{BAD MISS} AND THE RUNNING EXTREMELY RICH ISSUE ,THE ENGINE LIGHT WAS NOT ON AND THERE WAS NO CODES STORED,LIGHT CAME ON ABOUT 1/2 HR AGO AFTER I CLEANED THE TROTTLE BODY.I AM THINKING O2 SENSOR,BUT DONT WHAT TO REPLACE IT IF THERE IS AN MANIFOLD ISSUE.ANY SUGGESTIONS,PLEASE HELP AND THANKS IN ADVANCE:banghead:

If the O2 sensors were the problems USUALLY the check engine light comes on, but not always...I think the 02 sensors may be your problems here and would be cheaper to replace than a manifold job. However if there was a crank in the exhaust/intake manifold it WOULD run pretty rough and there would be a miss in the engine.

sounds exactly like problem i'm having with my 93 jgc. i replaced the O2 sensors, along with the IAC, TPS, CPS, ignition coil, new wires/plugs, new distributer cap, cleaned the throttle body, and finally the exhaust manifold. the jeep still runs rough. my next thought was the vacuum lines, but all are good and intact. you might want to check yours, though. let me know if you get it fixed. i've been going through it for a few weeks now and have just about reached the breaking point

thanks for the responses,i have also now replaced every think i can think of ,i am stumped,its very humbleing to say the least if any thing the bloody thing is worse,tomorrow i am bringing it to the dealer ---last resort---i will let you guys know what if anything they find,where i have a feeling they are going to tell me my computer is shot. when i start the engine it blows black gunk out my tailpipe at least 5ft away from the vehicle but as it warms up the black smoke becomes normal exhaust smoke,but engine still misses.seems to be alot for water coming out the tailpipe mixed with black carbon and it smells like gas.

.....when i start the engine it blows black gunk out my tailpipe at least 5ft away from the vehicle but as it warms up the black smoke becomes normal exhaust smoke,but engine still misses.seems to be alot for water coming out the tailpipe mixed with black carbon and it smells like gas.

Sounds like it's running VERY rich.

O2 and CPS were my first thoughts also.

I have had the same problem, I did alot of replacing of parts just to find that it was the EGR Valve. It would hold a vacume, but it was allowing air to flow past on the inside.

I have a 2004 jeep grand cherokee doing basically the same thing it comes in missing trrowing a missfire code and a lean condition on bank 2 yet all 3 plugs on that bank will be almost plugged with soot ,and also if you rev it up it throws black soot all over,i have replaced coil pack,all four o2's,fuel filter,checked cat (3%back pressure),even the costly computer yet aftetr 3-4 weeks it will foul out those back 3 plugs due to the pcm thinking the engine is running lean so it increases the fuel till it fouls them.

Am about to check egr valve but am seriously stumped.