I have a problem with my 86 Iroc-Z. The fuel pump is whining in the tank, not all the time but usually after I have driven over about 1 hr, or if its a hot day then I can only get about 30 min out of it. On colder days I dont seem to have any problem. Any way, when I noticed my pump whining in the tank I took off my gas cap and was supprised at the amount of air pressure that was coming OUT of the tank. Some people have told me that I must have been mistaken and that it was air going in and not out. I assure you this is not the case. The tank is way over pressurized. After the car sits for a few hours or I relieve the pressure for about 30 min the pump will stop whining. On the bottom of the tank is a vent. The vent has a small white or green plastic piece with a spring inside and a valve of some sort. I took off this valve and cleaned it with soap and water, then submerged it in wd-40. I had no problems for a few weeks, untill the weather got a little hotter. I dont know if this was a coincidence that everything was ok or if it was due to my cleaning. Does anybody have an ideas on what to do??? Here is a pic of one that i found on another car. The location for this is under the left hand side of the fuel tank. Also if anybody would have the maintenance manual for an 86 ill try and figure it out myself. But I have tried everything. I just had the fuel pump replaced with a Bosch one , I didnt have any problems with the ventning untill I had the pump replaced. The other pump was totally burned out, and I was stuck on the road.