If you have an O2 sensor, your O2 sensor will not read exhaust gases properly which may cause the ECU to make the engine run rich. Yes. Holes close to the engine in the headers may also cause...
Its a long shot but... If you have a leak in the exhaust before the oxygen sensors, the sensors will think the engine is running lean. The computer will compensate (from incorrect input data) by...
Just having a hole in the muffler won't cause smoke to form. Any smoke coming from an engine is caused by either environment changes (white smoke while engine is warming up), or an engine burning oil...