Hi guys,
does anybody have any idea why there occurs vacum in my gas tank (TPI, '89gta)? Every time I take off fuel cap after the ride there's sound of sucked air. I wonder how it effects on fuel pressure...
Thx in adv.
Mike

 

do you have a vented gas cap? if you do, then it may be clogged. get a new one.

 

i doubt it is a sucking noise but a pressure release noise, the tank ends up pressurized as you drive around. the charcoal canister has a check valve that controls the tank pressure and sends excess pressure and vapors to the engine to be burned.

 

Mine does the same thing- does this mean the charcoal canister isn't working properly? how would I test it?

 

This is sound of air flowing into tank, fillin' empty space after certain volume of fuel has been pumped out. Also I can hear sound of tank walls shootin' when there's been lot of fuel burned since prev. cap releasing

 

if your sure its the tank sucking in air check the valve right in front of the charcoal canister. the tank should end up pressurized to a point that is normal. put sucking sounds like the line/valve maybe reversed, so instead of building pressure and releasing it is drawing down a vacuum.

theres nothing wrong with the pressure release sound when you pop the cap off and i doubt that vacuum is doing any real harm either, but if the system is working right you will get the best gas mileage.

oh the emptier the tank is the louder it will be, normal.

 

OK, I'll check the valve tommorow. Thanks