Nissan Altima cranks, but won't start. Open the fuel tank, it starts. Gas tank vent? Clogged vent line? Gas cap?

Is it harder than normal to remove the gas cap? If so , it's bad cap. When driving it will create a vacuum pressure in your tank and if that pressure cant be purged then it will not let the fuel move. Now if you remove the gas cap and then put it back on and the car does start replace the gas cap

If the car sat, would bet all the money in my pockets that it's bad gas. Adding fresh gas won't solve the problem. You need to add a fuel stabilizer ( purchased for under $10 at Autozone) that you just add directly to the tank.
It could also be the case that the coil wires are dry and cracked from sitting, cause sparks to ground out.

Whenever your car won't start it is always one of three things-- fuel, spark or air. I hear you saying fuel is coming in, but to be sure you could try spraying a quick spray of carb cleaner or better yet starter fluid into the air intake and see if it briefly starts. If it does, then shuts down immediately, it's a fuel issue.

If not, then it is likely spark (air is usually not restricted but you may as well check the air filter and throttle body and make sure they aren't clogged. )

Check the spark in each cylinder. The problem could be a bad coil or fouled plugs.

If fuel, air and spark all check out, then the problem could be timing but this is highly unlikely.

check your fuel rail for fuel pressure. see if your getting enough gas.

Its possible you have air in the fuel line which would take a while to run out. Its also possible you clogged up the screen in the tank for the pump.
A mechanic would check fuel pressure at the injectors and probably replace the fuel filter.

I would check the fuel pressure with a gauge.
You could have a blockage in the gas tank.

One of the most common causes, is blockage in the venting system from fuel entering the vent lines and into the charcoal canister, the fuel gets absorbed by the charcoal canister causing it to swell and block vent lines. the gas tank contains both fuel and air. when you fill it up the gas displaces the air and the air has to go somewhere. but the air that is displaced is full of gas vapor so the gas vapor goes to the vent lines and into the charcoal canister, when the charcoal canister swells up it prevents the air from escaping the tank, canister could be clogged,canister filter may need replacement,electrical connection to the close valve may be open,canisterf might be damaged,purge valve from canister might be clogged,vent hoses might be clogged, the vent hose could be clogged, or the vent hose may have a kink. all this is caused by overfilling the gas tank, getting that last drop of gas in the neck of the fill tube.
good luck!

HI,
If you mean the fuel line,start the engine, then remove the fuel pump relay , when not enough fuel pressure to run the engine, it will die and line will be depressurized. The tank itself only has minimal pressure which is vented. Removing the filler (gas) cap will relieve any excess pressure in the tank...Mike

For an engine to fire you need 3 things; fuel, air and spark. I assume your air filter isn't extremely clogged so let's move on to fuel and spark. You could have a clogged fuel filter, water in the line or a bad fuel pump. Turn the key to accessory and listen for a whining noise from the fuel tank area, that would be your fuel pump. If you don't hear anything it could be that. If it's water in the line go to walmart or auto zone, buy some ISO HEAT for like $2 and pour it in the tank. If it's spark, your battery might be in such a weakened state that it cannot produce the cold cranking amps needed to start your vehicle. Try attaching jumper cables to another vehicle and see if it works

check spark plugs and wires out first. was there alot of moisture in the air? use some fuel injector cleaner in gas tank

Sounds like either the fuel pressure regulator or a clogged fuel filter.