Hey guys!! Need ur help! I have an 88 Iroc 5.7 and Just put a new cat on Monday and now I noticed that when I get out and close the door, a sound like a rush of air (like someone punctured the back tire) comes out from under the car.
Now I will say in the past we have been having issues with the gas tank bumpin so we replaced the gas cap to a new vented and changed the fuel filter.. then gave up on that project... could this be the tank acting up?
Or do you think the cat may be leaking at one of the connections.
I did test by loosening the gas tank and it did release pressure.

 

Sounds like you have pressure build-up in the tank. Check out this thread, it may give you an idea what is happening. GL!
https://www.thirdgen.org/forums/hist...ht=evap+system