Negative Boost
 

I don't understand why the boost guage goes into the negatives?

because its not boost at that point, its vacuum.

http://www.bonnevilleclub.com/forum/...15&highlight=A

All motors will pull the fuel and air mixture in like an old style carb'd engine. In this case..your PCM is programmed to save you fuel and power when not needed and therefore the engine draws in the charge instead of being force fed.