How would he have felt pain when Boddicker stabbed him in the chest?
Who says he "felt pain" if he's an effective machine pain shouldn't be a process he's capable of. That'd be inefficient for a machine. It's possible in "reaction" he had to being stabbed was due to internal machinery/components being damaged and he was reacting to that but I doubt it was, strictly speaking, "pain."
It was sort of Robocop's "Check Engine" light coming on.
One thing I never got, and this is a trope in all cyborg movies, is why he needs a HUD/GUI. We know it's not part of the visor as we see him with it when he loses the helmet so it's something being projected into his vision (which we're shown is a graphical representation of the world that can be scrambled and pixelated further suggesting he doesn't strictly have "eyes" so much as he has "vision processing." and his physical eyes are just more of the "make him look human as possible" thing.
But anyway, the HUD he has (along with the HUD/GUI the Terminators have in those movies) seems redundant for a machine that can "think" these things and already know them. Does Robocop with a computer memory and such really need a visual reminder in his "vision" on what his directives are?
Obviously not since the fourth one impacted his decision making without him knowing it. Same thing with things like the playback, he shouldn't need to see a video of this and just be able to "know" it or think it anytime he wants.
Again, this is a common trope in movies with characters like this but it doesnt make sense. Same deal with "Terminator" where we see a visual interface which, logically, they wouldn't need. Anymore than my CPU needs a monitor inside of it to see what's on my screen in order to know what's going on inside the active memory.