Carbon in exhaust?

Ok, I'm sorry if this was talked about in some previous post but i couldn't find any answers. I have a '98 blazer with 90,000 miles on it and I'm getting what I think is carbon built up in my exhaust pipe. I never noticed it before untill I got my new exhaust system and now I have to keep cleaning this layer of black stuff out to keep my exhaust tip shining. My exhaust also smells pretty bad when the engine is fully warmed up, like rotten eggs almost. bad cat maybe?

rotten eggs = bad cat - yes - the blackcould be coming from a failing 02 sensor - they tend to limp by forever without setting codes - changed mine last week ( same symptoms and problem fixed ) my sensor failed saying i had a lean exhaust so the pcm would richen it up- when i throttled it in park i could spray a line of black carbon on the road .

bad cat, sounds like what i have, any suggestions to where i can get a nice cat for my 97 4dr

rotten eggs = bad cat - yes - the blackcould be coming from a failing 02 sensor - they tend to limp by forever without setting codes - changed mine last week ( same symptoms and problem fixed ) my sensor failed saying i had a lean exhaust so the pcm would richen it up- when i throttled it in park i could spray a line of black carbon on the road .

wow, i dont think mines that bad yet but a few days after cleaning it i can wipe my finger on the inside of the ehxuast pipe and get a nice black finger. its really embarrasing having fingerprints in my tailpipe :eek: . I'll definetly have to check into the o2 sensor. what brand do most people reccomend?

alrighty, I got my o2 sensors replaced. that was one hell of a day, more like a day of hell. One of my sensors i guess got siezed up or was overtorqued when it was originally installed because it took every muscle i had to get it out and when i finally did the threads were all kinds of messed up, so i called some muffler shops to see how much they would charge to get a new o2 fitting welded in and it was way more than i was going to pay, so i got a hold of a tap and just cleaned up the threads that way so the new sensor would fit. everythings good now, i really hope the o2 sensors were the cause of my bad gas milage/carbon.

oh and one thing i noticed was i had to drive to school without any sensors in and i never got a check engine light, i thought that was kinda weird shouldn't a light have come on? I know the bulb works because it comes on when i turn the key to run w/o starting the car and when i unplug my MAF sensor. i just thought that was kinda weird.

did it fix the problem . check engine light likely wont come on even when the 02s are disconected -- you'd be amazed at how common it is to be driving around with a failed 02 sensor that a fly by night mechanic could never find ..... when everything else checks out a good mechanic with a scope can pick out the bad 02 - voltmeter will work sometimes but only when the sensor is dead - the measurement is in millivolts - but even thats not very conclusive since the sensors get slow over time and cant keep up with demand -- the wave form on a scope will show this .


also make sure the new exhuast is welded and not clamped and isnt leaking anywhere -- air can get sucked in and cause the 02s to read lean which would make the pcm add fuel - which also will give you black pipes .


for best performance most 02's should be replaced around 50,000 kms doesnt mean they wont last longer - but they will get slow .

eeh I'm still getting black pipes, maybe not quite as bad but none the less black. Ive done everything blazerLT reccomends on this threadhttp://www.automotiveforums.com/vbulletin/showthread.php?t=453370 except change the spark plugs, could that cause it to run this rich? I have a feeling the previous owners were the kind of people that would buy some kind of chip like those juice boxes on ebay or mess with the computer somehow, How would i check to make sure everything was good with the computer?

thanks,
Josh

Has the engine ever been decarbonized? This is done by putting a cleaner through thte intake as the engine is running. People do it various ways, but I usually get a good cleaner(GM sutff, I forget the name, I think its Cleens) pull off the PCV valve and I run it straight through the PCV valve. People, I think BlazerLT did it this way, used water, using the same method to clean the combustion chambers. For some really carboned engines, decarbonizing does wonders like night and day, it just depends on the overall health of the engine.

Do you suppose that there is no problem ? I can't think of any car on gas that doews not have a black pipe inside where you could wipe it with your finger and have to wash the black off.

Do you suppose that there is no problem ? I can't think of any car on gas that doews not have a black pipe inside where you could wipe it with your finger and have to wash the black off.

I agree, it sounds more like soot, a natural byproduct of combustion. Go check the exhaust pipe of a newer vehicle in the parking lot and see if it passes the finger test.

Do a tuneup including all the usual tuneup items. You do't have to do the wires.

90,000miles probably means the plugs are just about shot if they are original.

Use AC Delco Platinum plugs only gapped properly.

Did you get the cat replaced yet? That was what we told you to replace.

Smelling like rotton eggs means it is poisoned and needs to be replaced.