Pleateu at ~160*F
There's a pleateu at ~160*F where the collagen breaks down and all the "magic" happens. It's not unusual for the meat to sit between 160~175 for hours.
That said, a 4# pork butt should get to 190*F in 6~8 Hrs (1-1/2 ~ 2hrs/# rule of thumb). 9HRs is a bit too long...