Way too much pressure/heat in gas tank

I've been having this problem ever since I had the fuel pump replaced from this shop I used to go to that really butchered my car. I've taken it back several times but eventually gave up and just delt with it. But since I found this board, I thought maybe someone here could help.

Here's the deal. After driving the car around for awhile, especially when stuck in stop and go traffic, tremendous pressure starts building up in the gas tank. I know this because you can hear/feel the gas tank expand abruptly and it usually scares the hell out of me. Then, if you park the car and turn it off, you can actually hear the pressure being released slowly through the air canister in the engine compartment. That goes on for at least an hour or so. You can really smell the gas fumes as well. Then, when the car finally cools down later on, you can hear the gas tank contract and it always sets off the alarm. It's like a loud "bang".

My theory is that somehow the fuel is getting way to hot in the tank and causing excessive fumes which in turn causes pressure to continuously build. I know that some pressure is normal, but this is totally excessive.

Could they have put the wrong fuel pump in and it's putting out too much pressure which is causing too much heated fuel to return from the engine? They have already checked the regulator and said it was fine. Also, the car seems to run really rich now and smells horrible, although strangly enough, it did pass smog not too long ago.

Any help would be appreciated.

get a vented gas cap

... if you HAVE one (i think it came stock with our cars) then check it..make sure it's not screwed..

Nope, that ain't the problem. Already tried that. From what I understand, these cars did not come with vented caps. But I tried it anyways and that did not fix the problem. The vented cap cannot even vent the fumes fast enough.

There is something not right with the car. I think way too much heated fuel is being returned to the fuel tank for some reason which is causing massive pressure in there. Is it possible that too much fuel is being pumped up to the engine and since it can't use it all, it returns to the tank heated up? Or is it possible that the tank itself has some vented opening up top that might be blocked or something?? I'm telling you, this shop really butchered my car. They stripped so many damn bolts on my car it ain't funny. My transmission leaks because half of the screws are stripped. That shop is now out of business by the way...

just throwing out a suggestion, but maybe you need to put/replace the heatshield above the muffler. Idnt it right below the gas tank?

You probably have a problem with your canister vent line. The fuel that returns from the fuel rail is hot, when it gets to the tank it heats the other fuel causing pressure. This pressure is supposed to vent to the charcoal canister where it is absorbed by the charcoal then pulled from the charcoal into the intake to get burned. This way the fuel system is closed and no gas vapor (emissions) get to the atmosphere. Your vent line to the canister is probably kinked. Most likely when they reinstalled your fuel tank. If you get a shop manaul it should tell you how to identify the vent line and test for restrictions. Some other people on this site know a link to a diagnostics page. I haven't used it but have heard its good. Another problem may be your canister itself. If it is plugged it will not vent properly. But, since you said this happened after the fuel pump install, I would go after the vent line first. Hope this helps.

Thanks. I figured a line was problem kinked somewhere. It would not surprise me at all that this shop kinked the line considering how they butchered the rest of my car. The canister is brand new as well so that's probably not it. I will check out the diagnostics info.

In the meantime, you should probably leave your gas cap loose so it doesn't build so much pressure. Make sure you don't fill your tank, probably leave it 1/2 empty to prevent it from sloshing out of the cap. All that pressure is bound to cause a problem somewhere else.