#1 - make sure your temp gauges are all accurate.
#2 - crank the heat a little bit - it will NOT hurt a pork butt like it will other cuts, as long as you don't cook at 300 plus for the whole time. You said it's been on "almost" 4 hours...if you crank it up to 280°, you should hit 140 very soon.
#3 - you are going to get plenty of responses that tell you to throw the meat away because of the 40 - 140 rule. Some of these folks are a lot closer to "expert" status that I am - and I don't want to offend anyone.
However, if it takes you say 4 hours and 23 minutes to hit 140 degrees, I would press on and finish it. I do not endorse this for anyone but me... Never been sick a day in my life from food poisoning.
Once again - I'm not telling YOU to disregard the 40-140 rule, I'm only saying that i have before - and it's never hurt me. If you think about it....you are cooking the center of that pork butt to almost 200° - if it takes a TAD over 4 hours to hit 140, I don't run scared.
My disclaimer is...if I was trying to cook a pork butt 200° and after 7 hours I was only at 128°, I wouldn't press my luck THAT much...but 20 - 25 minutes, no big deal, IMO. These FDA guidelines are created to error on the side of caution
- so there is a little wiggle room, IMO.
Once again - that's how I think of it, but I would never tell anyone else to do it my way either.