Alright, I've been battling this for last year.

There is soo much pressure building up in the gas tank that when I unscrew the cap (after the car has been sitting for 12+hours over night) it hisses a bunch and the tank makes blumping noises.

Now, I removed the muffler from underneath the tank and only have one pipe coming out on the side of the tank.
Replaced the pressure relief valve that goes close to the rear axle.
Replaced charcoal canister.
Replaced the vacum diverter that comes of the vent line and goes to the canister.
Replaced the purge valve.
So far every canister I replaced has eventually filled up with fuel. Even with different purge valves. This leads me to believe that there is nothing clogging the vent line.
The system works, it just builds too much pressure to where it relieves it from the little vent vlave over the axle.

I need some suggestions.
The only thing I don't have checked are kinked lines, or miss routed lines. My canister is on the pass side which is kind of hard to miss route IMO.
Other than that, I am starting to think something with Fuel Pump. I am just not sure that the pump itself can do such damage?? Maybe its still working after I shut the car off (but I can't hear anything).

I need suggestions cuz I am at wits end with this crap.

P.S. THe rear end in my car tends to get really hot. It sits under the tank and the radiant heat could be causing the problem. Do you think this is something I should be looking into??

Thanks guys and gals

 

Alright

Checked all the lines, followed them all the way to the rear axle where they go into the tank.

Now, there are two lines, one is hooked up with the return line and the other one is hooked up with the canister. They are both the same size (from what I can tell).
Here is a pic and maybe you can tell me where these need to be hooked up.



I am not sure of any ill effect if they are hooked up backwards, but I'd rather have them hooked up the way they should be.

If you have a pic of your lines please post 'em here so that I can compare.

 

it is normal to build up quite a bit of pressure in the tank

 

Is it your rear that's getting hot or is it your exhuast? No idea where you're at, but down here people are having some issues with the multiple 100º+ days. Insulate your exhaust and see if it gets better.

 

Mine hisses when I refill. Even with a vented gas gap. Which may not work.

 

some pressure in the tank is normal, especially when the tank is low or near empty. Although exactly how much pressure is acceptable I dont know. I know on really hot days that my tank gets enough pressure that it vents and I can smell fumes inside the car when stopped at a light or something, so if your system isnt venting then your cap is probably defective. Even new caps can be defective, so try another. I use a vented cap, and like said above even it holds some pressure.

 

Yes, and Yes,

The days have been really hot here. Last two days its been over 100 and I've been driving in the middle of the day for over an hour or so. I understand that these cars do that, but this morning after it sat over night it hissed more than it usually does on "normal days".

I actually noticed that my valve that comes from the vent line and goes to the canister was making buzzing noises when I stoped today at school. So, I just happen to have another one laying around (because I ****** things like that at the JY) and I replaced it and WOW. My tank did not build nearly as much pressure. It was ridiculous that after 1 and a half hour drive my tank had a lot less pressure and it did not hiss out of the little vent.

It was around 90-95 today and I drove in the middle of the heat. No problems with the vent, just a bit of fuel smell at the canister and I think thats from having it fill up prior to me changing the valve.
So far it looks like I might have fixed the problem, probably temporarily.

I know the tank needs to build up pressure, however its not supposed to build up more pressure to where it vents out of the rear relief valve. That valve is designed to prevent the tank from colapsing and the "secuirty" feature is to vent the fumes out if they build too much pressure.
I owned a third gen before this that did not release pressure like that on hottest of days.
TPI systems are running much more pressure and I can see that being a problem overall. The design of the tank and the placement of the exhaust does not help our system either.

I right now have a glass pack mounted on the I-pipe before the axle and have the pipe just go over the axle and straight out. So, no muffler underneath it. As of now I have replaced every single component in the EVAP system. So far so good.