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1996 corolla: fuel tank..cap..a big air pressure release and I..vacuum

Resolved Question:

1996 corolla fuel tank is pressurized alot!
removing the cap results in a big air pressure release and
I can hear the tank creaking back to its normal un-inflated shape.

Should it be under pressure--or under vacuum?
Submitted: 4 years ago.
Category: Toyota
Expert:  Toyotapro replied 4 years ago.
Hello and thank you for using just answer! I would first replace the fue cap with a newfactory cap. This is the most common issue. If a $20 cap doesn't fix it then you have an issue with a restricted eap system but that would be very unusual.
Customer: replied 4 years ago.
But please do answer this part:

Should the tank be pressrized...or should it hold a vacuum?
Expert:  Toyotapro replied 4 years ago.
The tank should be slightly pressurized, not to the point that it sprays fuel out but slightly. The fuel cap has a pressure valve on it that controls this and the tank also is controlled by the evap canister. If your tank is over pressurizing then the valve in the cap is bad.
Customer: replied 4 years ago.
The answer you gave makes sense I think...
But is the tank supposed to be pressurized...or vacuumized?

Inquiring minds want to know...
Expert:  Toyotapro replied 4 years ago.
As I stated before the tank is supposed to be pressurized.
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