Fuel tank not venting properly?

Whenever I remove the fuel cap after driving my 91 Caprice any distance, the tank has a vacuum condition. The car also seem to hesitate at slower speeds. I'm thinking the fuel tank is not being properly vented. I bought a new gas cap from the general, but that's not the problem. I bought a second one in case the first was faulty, but the condition still exists. Has anyone else ran into this problem or have an idea of what may be causing this? I don't have a service manual yet to familiarize myself with the fuel system, as I just bought the car (has 103,000km on it now). Thanks. Tom

ok i have the same car, do you mean when you take the gas cap off it sounds like it is farting lol? b/c if that is what you are talking about then everything is fine, a fuel system on a car is a sealed system witch means nothing can get in and nothing can get out. that way you dont get dirt or that kind of stuff being sucked in your motor, as far as it being sluggish on the slow seeds i also had this problem all i did was change the fule filter and everything was better. i hope this helped

You got quite a collection of cars pontiac. Can you get a vented gas cap for that? There has to be a vent somewhere cause when the gas comes out air goes in.

The car has a new fuel filter and the gas cap was bought from GM last week specifically for the 91 Caprice. I'm going to try it on my sons 91 Buick Park Avenue and see what happens. None of my other fuel injected, or carburated, cars have ever had vapour lock, so I thought it might be something serious. I'll check they installed the fuel filter in the correct direction before I try replacing it. Thanks. Tom