I have a '97 XJ Country with the 4.0L, with a new cat, muffler and front pipe. the O2 sensor behind the cat is new but the one in the front pipe is off the old front pipe. For some reason the engine is running rough when it is warmed up and leaves a soot spot in the driveway/road, leaves a black cloud when i hammer the peddel and burns gas something ferice. Can anyone tell me what i may try/ what will work to fix this... i love my jeep and i am getting ready to burn it!

 

Black smoke= rich condition hence poor fuel economy, O2 sensor is good place to start. the downstream O2 tells the ECM that the cat is doing its job IIRC. Replace front O2, if that doesnt help look into a leaky injector.

 

x2 On the o2 sensors. The rear really does nothing except make sure the cat. is doing its job.

 

thats what i thought ive heard of people knocking them off wheeling with no adverse effects

 

Hey i have the same problem with my 88' 4.0, replaced the O2 and it doesn't leave black stuff on the garage floor anymore but it idles high, round 1500 rpm, and chokes out and leaves a black cloud when i mash on the exhaust... Leaky fuel injector or something else?

 

C'mon everyone say it with me SeaFoam!! I have a 96 and that stuff works wonders. Although I am a newb at this stuff I would imagine that if black stuff is coming out it is probably building up carbon whereever it is coming out of. and I can almost guarantee that it will help. Good Luck!

 

cool alright i used that "guaranteed pass" additive thinking it would work, maybe that's the cause of the smoke?? Would it be ok to use Seafoam after i used that stuff? Seems like Seafoam is a wonder drug for jeep, well from what I've read anyways!

 

my 99 grand cherokee is burning black smoke when i accelerate and jerks when i drive sometimes. when im going up hill i feel like im the slowest person on earth because my jeep just doesnt wanna go. whats wrong?!?!?!

 

when is the last time you changed the transfer case fluid? also the black smoke could be a bad oil leak from your intake valve gasket. don't quote me on it but those are two things I would check out.

 

^ not trying to be a *****, but start your own thread here ----->https://www.cherokeeforum.com/newthr...=newthread&f=5
Not only will you get more help, you wont "crap up" this thread with two different problems/vehicles.


PO, I would change your first Oxygen sensor and look for a vacuum leak. If oxygen sensor doesnt do it, and no vacuum leaks, you may have a bad MAP sensor.

 

im having the same problem. burning rich, heavy black smoke, slow going up hills and accelerating. and its like its not getting constant steady feul flow when running. which o2 sensor do I replace first??

 

Everyone having this problem, replace THE FRONT 02, this has been covered a million times, it is a great place to start. SEARCH!

 

I have the same exact issues as the OP on my 99 sport.
Soot spot in driveway, smoke when I mash it, running rough and chugging..
Everything on the internet points to the O2.. Will be replacing mine this weekend. Let ya know if it solves the problem. I'm almost 80% certain it will though.
Don't let me forget and I'll post back here for anybody wanting to know.

 

For anyone interested, replaced the upstream O2 this morning, and took it on a test drive in the country.Floored it a few times to blow the soot out of the pipe. 1st time was dark black, second was 50% less, third time was almost gone. After that, no more black smoke, mashed it down a bunch of times, and no more smoke. No soot, no nothing, and better horse power. It's running like a champ now.. Drove 50 miles, from 65mph to in town 20mph stop and go..

So there ya go.. Replace the O2..

 

That pesk old O2 sensor. gets yah every time.