I think if the sensor maxes out it goes to the top of the screen and disappears like you said, no scaling options that I know. The solution is to get a sensor that has more range so that it doesn't max out. A 150psi sensor could max out but a 200psi one won't. Pain because it will disappear on the graph but if its above 150psi you are good and thats the important thing.
Two questions... what psi is your sensor rated for and what are the alky psi sensor settings in the laptop you use to connect/log with (File>Auxiliary Analog Sensor Setup) ?
It's the log kit straight from Rzr.
The above pic is a screen shot
The above pic is a screen shot