92 cadillac deville 155k 4.9

[quote:410474054c="alberts cobra"]I have had this car for 6 years never had any problems with it. Then all of a sudden I noticed black smoke coming out of the exhaust. It runs fine I've done a tune up on it and changed the gas filter, dont know what to do and if it costs too much to repair I'll get rid of it.[/quote:410474054c]

In that 6yrs have you ever change the oxygen sensor/s or get the fuel injection system clean.