dark puffs of smoke on hard acceleration..
My every day driver is a 1989 Mercury Grand Marquis LS. It has 87k miles, and burns no oil between 3k oil change intervals. However, lately, I've noticed a puff of dark smoke coming out of the exhaust, only on HARD accelerations. I have not been doing any interstate driving because I've been trying to conserve gasoline lately. My speeds hardly reach 60 mph. The car idles fine and does not miss. Does it sound like I just need to open it up a few times on the interstate, to burn off the carbon? I've heard about doing that every now and then. But, that was when everyone was running on leaded gas.