I aquired the Pololu carrier pololu.com/catalog/product/1134 for the small sharp IR sensor. Plugged it into my breadboard, supplied the 5V and used a PIC to measure and display the output.
Supplying 5V to the sensor I get
Distance>10 cm (LED off): 3.90V
Distance<10 cm (LED on): 0.85V
There’s no inbetween value. It’s like a switch. Anything below 10 cm outputs 0.85, anything above 3.90V
Yes, that’s exactly how it’s supposed to work - it is a digital sensor, not an analog one. It will probably work as a digital input to your PIC even without pull-ups (since the carrier board pulls the line up with the LED), and your PIC probably has optional built-in pull-ups on some of the pins anyway, if that doesn’t work.