Gas leak?
 

Today I was driving home, my car running just fine. I get home and I swear I smell gas when I get out. I look behind my car and there is a little stream of gas behind where I pulled up. I look at my gas cap and I can hear my tank trying to suck in air. My cap is also a little loose. I open my tank cap and the air rushes into the tank for a couple seconds. Not just a tiny bit like when you run your car real low and you go to fill it up, but a lot of air goes rushing in there, plus my tank is 3/4 full. I think the gas was coming out of my tank cap because there is gas in the lip beneath the cap outside the tank and it looks like that is where the gas was leaking out.

So after this happened I decided to take my chance and see if it did it again, and it did the exact same thing except the cap wasn't loose this time. It still leaked.

So at least my tank isn't leaking, but does anyone have any idea what is going on? It is like the air is being sucked out of my tank and gas is being forced out my tank cap because of the pressure.

Thanks for any ideas, Mark

Check you evap canister (passenger front frame rail behind radiator). Make sure that the lines arent crushed...
Sounds like you are not venting the pressure of your tank into the canister, to later be "introduced" into your intake (thats emissions language speaking).
Look at the filler tube for leaks where it meet the rear fender, and where it enters the tank too.

Maybe your gas cap is bad. The fuel tank is supposed to hold a pressure of about 1.6 PSI ( that is what the cap is set at ). I'm not sure if the air is supposed to come in from the cap when running or if there is another one way valve somewhere to prevent the vacuum building up. Maybe its in the evap cannister like Darius suggested.

Gas leak?
 

I really need help! Today i rplaced my therometer stat mainifolds on a ''2003 gt mustang'' and i took everything apart that aplies to puting the manifold gaskets on including the intake and now WHEN I PUT EVERYTHING BACK 2GETHER my car wants to start but want fully start and also gas is leaking from my passenger side fuel injector..... Please help me do i need to replace the fuel injectors or the injector ring??