P0440, and gas cap vacuum?

[PlazaEJ]

My problem seems to be a little different than most, with EVAP problems.
I didn't start getting the dreaded P0440, until a couple of weeks after having the fuel pump replaced. At first it didn't seem to appear until fuel level dropped to 1/4 of a tank. Also, when I removed the gas cap, it sounded like the fuel tank was under vacuum, not pressure. Is this possible, or am I just incorrect in what I'm hearing. No problems in drive-ability. So, I wouldn't think it could be vacuum.

Whatcha think? Purge solenoid, vent solenoid, or both? Or, maybe, canister?

Thanks,
EJ

 

[PlazaEJ]

UPDATE:
I've been watching, and tracking the DTCs. Still getting P0440, only when tank drops to less than 80%, as per service manual info. However, I deliberately waited to fill up, after running through an entire tank of gas. When I opened the gas cap there was a loooong hissing sound, and it sounded like vacuum, to me.

I'm guessing there's a problem with the vent solenoid? I crawled under and took a peek, but I don't see anything broken, disconnected, or out of place.

Could the vent solenoid have gone bad?

EJ

 

[ccapehartusarmyINF.(ret)]

i just fought with this problem for about 3 months i kept getting p0440 with a brand new gas cap
finally i replaced my vent valve solenoid also the purge valve solenoid thats on top of the throttle body the vent solenoid is above the rear diff the last thing to replace is the charcoal canister the big plastic box next to the tank those are supposed to last the life of the vehicle but its possible if your in the habit of topping off yer tank its possible fuel can get into it by way of the evap hoses and ruin it
on thing that sucks is the drive cycle for the evap system test takes along time
ive also noticed since ive had problems with the evap system i run outta gas when the guage shows quarter tank

 

[smcnair]

This fixed mine when I was having the problem...

Canister