Black smoke on startup

[oz_ls1]

Hi Guys,

Im new to this site.
I have an LS1 GTO. On startup during the engine being semi warm the engine makes a pinging sound followed by a puff of black smoke. It occurs when I take it for a drive, switch it off and let it sit for 30mins to an hour.

Cold starting the problem is not present.
Hot starting the problem is not present.
Starting the engine a second time after the problem has occurred above - problem not present.

Could it be a Coolant Temp sensor? O2 sensor problem? Maf?

Any help is greatly appreciated.

Thanks.:Pics:

[GOT1GOAT]

Dont know but might be a catylitic converter prob. At my work, theres a van that did that and it was the cat. Have it checked out and good luck. Oh, and Welcome Oz