A cooking grill with a cooking chamber, pellet fuel combustion unit, and ash cleanout system for releasing retained ash from the combustion unit through an access door without requiring the disassembly of the upper components of the grill. The combustion unit has a first end with a first end opening, and a second end with a second end opening. The ash cleanout system includes an access door adjacent to the second end, operable by a user from a position external to the cooking chamber through a pull link, and capable of a first position wherein the second end opening is closed to generally retain ash within the pellet fuel combustion unit, and a second position wherein the second end opening is open to release the retained ash to a separate removal location.