Recently I have started having a weird problem with gas tank pressure build up. If I fill the tank, not over fill but just until the pump clicks off, if I drive a few miles after the fill up and stop and park the car pressure will buildin the tank to the point that gas will begin to spew out the gas tank fill neck. I have checked the charcoal canister and its relief valve are working correctly.
Any suggestions on what might be causing this.

 

Might just be a bad gas cap as they usually contain some type of pressure/vacuum relief valve for venting. Go to a junkyard and pull a new (to you) gas cap from an sc and try it out.

 

i had that happen with my 240sx, changing out the gas cap fixed it.

Marko

 

When I got to fill the tank at the pump I can hear the pressure release as I under the gas cap.. similar to opening a soda bottle. Suggest I change the cap then? Didn't know if that was really an issue.

 

Actually I think your cap is working correctly

 

i have to same issue ,it's like you pop open a soda bottle
canister or really the filler cap ? i thought the filler should be airtight and the pressure would be relieved through the charcoal canister

 

I know I can hear the pressure released when I remove the gas cap. Don't know anything about the charcoal canister..

 

The fuel/tank systems on our cars is a pressurized system, so when releasing the.gas cap you should hear a slight release of pressure if all is working properly. OP your problem.may be that the cap isn't holding & allowing the pressure to blow the gas out your fill stem.

 

ah thanks for clearing that out Ramblerman
nothing to worry about then

 

Can anyone else vouch for the increased pressure? Most cars vent those fumes back into the intake manifold... does our system only vent off after a certain pressure level? Mine also has a ton of pressure release when I remove the cap.

 

Mine is the same way. I've had a few gas station attendants express surprise at how much pressure there is (we can't pump our own gas here), but everyone here says it's normal for SCs, so I assume our cars are just a rarity that way.

 

UPDATE: Bought a new gas cap and that solved all the problems. Thanks to all of you for the suggestions.

 

Do you mind clarifying? Did the pressure "whoosh" disappear entirely now?

 

I got the whoosh as well on all 4 of my SC's. It seems to be another one of those SC things.

 

I was not getting a whoosh. My gas cap was not sealing so gas vapors and sometimes gas was escaping and the fumes were coming in the cabin, With the new cap I do get the whoosh.