2009 v10 creating excessive vacuum pressure i can hear it trying to suck vacuum around the gas cap. possibly bad cap but i think it is some thing more

 

Excessive pressure or excessive vacuum? They are opposite conditions.

 

The caps on these fuel systems have been completely sealed for quite some time.

If there's vacuum OR pressure, something is wrong with the evaporative emissions system.

Can you scan for codes with an OBD-II/CAN scanner? Autozone or some other local parts store might have something you can borrow for a few minutes.

Record all the codes (if any) and report back. There might not BE any, but it's worth a shot to check.

 

there are no codes and the tank has excessive vacuum and it is trying to do all the venting through the gas cap

 

Sounds like either the charcoal canister is clogged, or the solenoid isn't activating. I don't know a whole lot about what the later trucks have for evaporative emissions.

But usually what happens is when pressure in the tank builds up, it feeds a charcoal canister that collects the vapors. When the engine is running, the computer opens a solenoid (purge valve) between the canister and the intake manifold to suck the vapors out of the canister - a "purge".

If the engine is off, and there is vacuum in the tank, something "ain't right"