Pretty hard to tell with no other clues or observations. Black smoke is a result of too much unburned fuel. That can be caused by a problem or it can be a result of the Engine Computer requesting too much fuel in response to an incorrect sensor reading. Normally there will be a diagnostic fault code and when an increase in emissions is involved, the Check Engine light should turn on. Have you checked for fault codes?
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Tuesday, January 17th, 2012 AT 3:30 AM