Blowing black smoke

I have a 94 Grand-Am (my son's car) with a 3.1L v-6, auto trans that is blowing black smoke. It idles and accelerates fine but has poor gas milage and blows some black smoke while idling and when you stomp on the gas. This engine has about 160,000 miles on it and I am suspecting the fuel injector may be just plum wore out. I am wondering what other things I might need to check with these conditions. Like I said, no flooding out or preformance issues other than poor mileage and the black rear bumber. Thanks in advance for your help.

Its definitly a fuel issue. I'd check out the fuel pressure regulator and fuel injectors before going after anything else...

No kind of check engine light on? Any kind of misfire?

Thanks for the feedback. No missing or backfire at all. This engine just sits and purrs at idle and has great power and acceleration. I have an intermittent service engine light that comes and goes. I have not had that diagnosed as of yet. I put new plugs in it a week or so ago but the old ones looked fine so I did not do anymore to the ignition. I am going to replace the thermostat and flush and fill the cooling system this weekend. This could be a potential for the check engine light and should eliminate any possibility of the temp sensor playing a part in fooling the fuel system to dump too much fuel into an engine that is not cold. Picked up a Haynes manual yesterday but it's of little to no help so I figured I would ask those here who would know more.
Thanks,
2001 Astro Dude