Black Smoke?????new Mechanic !!!!!!!!!

[very tired]

I have had my 89 300 at the mechanic for what was identified as a fuel problem. Would start thencut off. He has replaced the converted/y pipe and tune up. He called the day I was suppose to pick up and said he was worried because when the test drove he saw black smoke. Now he thinks there is WATER in the gas tank?????????????????????????????

Why is this "showing Up" now???????????????? I never saw it before!!!

Worried this mechanic does not have a clue!!!!!!!!!!!!!!!!