black deposits at tail pipe question

Discussion in 'General Chevy & GM Tech Questions' started by desertduck, Nov 16, 2009.

  1. desertduck

    desertduck New Member

    1. 2004 Silverado, C1500 LS, 4.8L, 70k+ miles. The tail pipe has black deposits, I know this is a telling sign, is it O2 sensors? Gas mileage and power are good.

    2. What is the OEM O2 sensor replace point? Replacing the up stream sensors is more important than the down stream sensors, yes or no?

    3. There have been "lean fuel mixture" codes that were corrected by cleaning the MAF & K&N air filter.
    .:confused:
     
  2. Truman

    Truman New Member

    to me it sounds like its too rich of a fuel mixture if you're getting black carbon deposits in the exhaust, could be a dying O2 sensor, and i say rich because when the O2 sensor reads too lean the computer tells it to run richer than it should, so it could be your problem. however which O2 sensor? i couldnt tell you unless your scan tool tells you which bank it is cause theres 4 of them
     
  3. vncj96

    vncj96 Epic Member 5+ Years 1000 Posts

    It doesnt REALLY mean there is anything wrong with it, many times that you stomp it it can blow some build up from within the intake and get all the way through to redeposit in the exhaust, and it can also run rich when you get on it just like a diesel does, granted it wont be nearly as much but a little can build up after a while.
     

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