What does it imply if when your removing gas cap at low fuel a huge swarm of air comes out?.cap is new.

This happened before emission code set.

.after keeping fuel level high an 3 clicks on cap .no codes?...even after 400 miles

What gives with these caps an levels of fuel effecting code [po441 purge valve insuffici7insufficiency]...an the air issue removing cap?

 

From what I understand about emmissions the cap is to let air in but not let fumes out. I believe the air pressure is normal, the cap is doing it's job. The purge valve may not be working. Purge valve let's fumes gather in cannister through engine vacuum when engine turned off, then, purged into engine upon starting. I would think if pressure in tank is great check the purge valve itself. Again this is the way I understand how it works in my truck.
Pressure may seem more prominent with a low tank cause more air space and larger volume of air.