Place spareribs in a large stock pot with barbeque sauce, onion, salt, and pepper. Pour in enough water to cover. Bring to a low boil, and cook approximately 40 minutes.
Preheat grill for high heat.
Lightly oil grate. Remove spareribs from the stock pot, and place on the prepared grill. Use the barbeque sauce in the saucepan to baste ribs while cooking. Grill ribs, basting and turning frequently, for 20 minutes, or until nicely browned.