dodge caravan pinging

Hi, I own a 1993 Dodge Caravan with 146,000 miles on it. The vehicle runs fine {starts ok idles ok} but when it gets up to operating temp. There is a slight ping if you step on the gas lightly. If you push the accelerator down so it downshifts it will subside except if I'm climbing a steep grade. I don't sense a power loss but I know the pinging can be harmful to the engine. What do I need to check or any suggestions on what specifically it might be. Thanks, Warren