My '89 Gen I (V6) has developed a disturbing condition... the gas tank does not seem to be venting. Previously, I'd often hear the vacuum hiss as I opened the gas cap, but now it's blowing vapor out (can feel and smell) when I turn the cap. I pulled the panel in the wheel well and checked all breather/overfill hoses... they seem to be clear, I can blow through them at least. Could this be b/c the EVAP cannister isn't purging? Would that be the solenoid valve mounted on the inner fender?

I'm considering drilling a small hole in the gas cap until I figure this out -- we're going over the 100 degree mark here in Texas, and I hate to think how much pressure is building up in the tank.

Any thoughts appreciated,
Bryan