What led you to the injectors? You know they didn't all fail at once. GM has a lot of injector problems but they almost always flow too little fuel. Black smoke is a sign of burning too much fuel. Usually that is because the Engine Computer is commanding too much fuel based on incorrect sensor readings. A sensor can partially fail and not set a diagnostic fault code, but most of the time a code will be set and the Check Engine light will turn on. Did you check for fault codes? If you did, what were they?
January, 15, 2013 AT 1:14 AM
Its reading code po191 I changed upper oxy sensor then did the injectors because it did not work