Fuel tank Pressure

[Stogie D]

Mornin Vetteheads - please chime in if you have info/knowledge on this subject - on my 1990, when I loosen the cap on the fuel tank to gas up, the pressure that is released is scary - it seems to be WAY more than normal or at least normal on every car I've ever had - is there a pressure release valve in the fuel system somewhere that could be bad? - what kind of fuel tank pressure is normal - this is my first Vette of this vintage so I dont know what is normal & what is not - Thanks, D.

 

[jmhorn52]

My 88 does the same thing. I usually fill up between a 1/2 and 3/4 when I am out, but even when I am under 1/4 there seems to be alot pressure released when removing the cap. My 2000 silverado doesnt have that problem

 

[vetteoz]

Blocked vent line to charcoal canister
You can access the vent line under the filler cap plate.
Disconnect the vent line at tank (LHS top) and where the rubber line to the canister (under drv headlight) joins the hard line on the inner guard .
Blow through.
There is a rubber hose section on the floor pan behind the drv seat that gets blocked with rust flakes from the steel lines over the tank.
Also possible that the vapour purge system is not purging the canister when it is supposed to.

 

[Jeff]

Blocked vent line to charcoal canister
You can access the vent line under the filler cap plate.
Disconnect the vent line at tank (LHS top) and where the rubber line to the canister (under drv headlight) joins the hard line on the inner guard .
Blow through.
There is a rubber hose section on the floor pan behind the drv seat that gets blocked with rust flakes from the steel lines over the tank.
Also possible that the vapour purge system is not purging the canister when it is supposed to.

Thanks oz, mine seems to be under an unusually high pressure also. Occasionally, I have left the filler cap a little loose, :L. Could loosening the cap cause my SES light to come on? As I sit here right now, I haven't even scanned for a code yet...gonna do that tomorrow.

 

[vetteoz]

Unlike later cars there is no monitoring of the evap system (tank pressure , etc) except for a check of the purge solenoid circuit wiring