Sprinkle salt and pepper over the skin of the chicken breasts.
Brush the vegetable oil over the grill grates and place the chicken skin side down. Do not touch for four minutes. Flip and cook for four more minutes. Then move the breasts to an upper rack or cool side of the grill, close the cover and cook for twenty minutes to 145 degrees F when poked with a probe thermometer. (Smaller breast halves will take less time to cook). If you like extra crispy skin, place back over the heat, skin side down, for a few extra minutes before brushing with the sauce as explained in the step in below.
In a small bowl, mix ketchup, maple syrup, vinegar, mustard, liquid smoke and salt.
Brush on sauce to coat, close cover and cook for ten more minutes, or when the internal temperature reaches 155 degrees F when poked with a probe thermometer.