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?

Answered by caradiodoc (expert)
17,319 answers provided

its reading code po191 i changed upper oxy sensor then did the injectors because it did not work

Response from mikecon24
2 questions asked

P0191 – Fuel Rail Pressure Sensor Circuit Range/Performance

Is this the description you came up with? I've never run into this code before.

Answered by caradiodoc (expert)
17,319 answers provided

maybe it was po171 i have to check again to make sure.

Response from mikecon24
2 questions asked