Black smoke coming out of tailpipe but there is no check engine light coming on

What is your question?

My 2009 Hyundai Accent has black smoke coming from the tailpipe I took it to a mechanic and he said nothing is coming up on the computer. It doesn't happen all the time but when it does it's a lot of smoke. I also noticed that sometimes the gas gauge is not working and I have to turn on and off my car. Please help!!!! What seems to make the problem better or worse? It's worse when I accelerate after being at a stop for a few minutes How long have you had this problem? The past month