I have an 86 IROC that has a fuel tank pressurization problem. Excess pressure builds up in side the fuel tank. It literally blows fuel out when the cap is removed after driving. I suspect the fuel tank vent valve. There are none to be found at any parts store or GM dealer. Any recommendations?

 

You'd probably be surprised to see how much crud comes out of the valve when you just take it off the car, and scrub what you can get at with soap and water, then rinse it off. Some people go the extra mile to break the thing open and clean the innards, but if you break too much you might find yourself in the classifieds trying to find another 30 year old piece of plastic to replace it.

 

I thought that little valve was to let air in to replace used gasoline. ....thought excess pressure was vented out via the emissions canister.

Certainly could be wrong.

 

I just started a thread with basically the same issue, so I'll just squeeze in to yours. My pressure triggers the gas pump handle every 2 seconds, and once full, gas spills out from the cap and down the side of the car. When I take the cap off, there's a pretty big pressure release. Drew gave me the same recommendation, so I'll check mine out as soon as I get a chance. Can someone confirm Abubaca's statement? Or at least elaborate on what happens in the canister? It's a 30 yr old unit so if there's something that could be clogged in it, it would be a good place to check

 

Pretty sure it works both ways. Two springs to control the valve opening in either direction at a set point.

Fast forward to just before the 2 minute mark.

 

Good info on this topic here:
https://www.thirdgen.org/forums/tpi/...eat-blues.html
https://www.thirdgen.org/forums/hist...ent-valve.html