Blac smoke means the engine is running rich and this would definitely increase the fuel consumption.

Is the Malfunction Indicator Light showing?
Is engine misfiring?
There are many possibiities and you should start with basics. A clogged air filter can cause it.

http://www.2carpros.com/articles/engine-black-smoke

Check above link for more information.

Answered by KHLow2008 (expert)
39,832 answers provided

No any malfunction sighn on the dashboard. Misfire occurs slightly if the engine is not started for about two to three days.

Response from jamesjemoo
2 questions asked

You need to perform the diagnostics as outlined in the link provided.

Answered by KHLow2008 (expert)
39,832 answers provided

I will thanx.

Response from jamesjemoo
2 questions asked

I took it for diagnosis, my crib is fine;A'l fill gas then I cruze wildly n safe. Thanx

Response from jamesjemoo
2 questions asked