99, when opening the gas cap you get a psfft noise- can t tell if its pressure or vacuum- is that normal?

 

Normal.

 

^agreed, nothing to worry about

 

Are you sure you are not opening a 2 liter cap??
Yea it's normal, it's relieving pressure

 

i think it has something to do with the vapors being released in the gas tank and when you open it, the pressure that was created is released, creating the sound you hear

 

for real??

 

its normal...what i dont understand though is when you go to check your gas cap and its loose as hell...then p0440.

 

I'd think its actually a slight vacuum, the air is rushing in to fill the void left by the fuel that you used???

 

Seriously? It's the left over vapors from your coilpacks number 1,3 and 5 that didn't detonate gas and it was forcefed into the gasoline vacuum line, your lucky it didn't rush back into your LIM and explode your engine...lol...you'll be ok.....

 

it supposed to release a little bit of vapors. i believe the gas caps are designed to hold only 2 PSI.

 

???Wha??? I was talking about the void in the tank itself, you must be talking about the muffler bearing or the flux capacitor...

 

I checked the description of the evaporative emissions control system in the FSM and it shows the gas cap as having both pressure and vacume relief valves.

Based on the description about it's operation, it seems to me any way, that if you unscrew the cap at a gas station or just just after operating the car, you should hear a vacume release (air rushing into tank) because the system is designed to prevent fuel vapors from escaping into the atmosphere so it burns them in the engine.

If the car is sitting in the sun on a hot day and you release the cap I would expect vapors to come out of the tank and it should smell, more definitely, like gas.

The FSM states that the cap should hold a pressure of 2.22 - 2.90 PSI and a vacume of just -.87 to -.48 PSI.

 

I'm impressed that you actually pulled out some legit numbers, meanwhile the rest of us were just goofing around and being smart asses. That's good to know

 

the gas cap on my 95gxe stopped go poooshhhhhh back in 2001 I replaced it and the evap canister + the evap purge vent control valve in 2008 which fixed the CEl but still no poooooooshhhhh,

 

better a smart *** then a dumb ***....uppet:

 

My maxima does it when I fill up, generally with about 1/4 tank left. My altima 2.4L never did unless it was way below 1/8 tank. Weird.

 

smaller tank