When gas tank is full it leaks

My first suspicion is that the car had been in an accident and was not properly repaired. Check all the hoses for exhaust gas recirculation and fuel systems. Particularly look for rubber hoses, large or small, that may be pinched, cracked or damaged. You will need the car up on a hoist and a really good flashlight. I might also help to fill the car with gas first, so any leaks would show up more easily. You aslo have some systems that are supposed to direct gas fumes to be burned. Try to check these.
I think you know never to fill the gas tank past the first "click", right?
Be blessed.

Did you ask auto zone they usually tell you what's wrong otherwise go to the dealer. As far as your fuel gage it may be the cause of all your problems as they are part of your fuel pump that's in your gas tank it should be able to be reaches either under your back seat or in your trunk.

I suspect you may not have enough fuel pressure.Fuel injection requires very high pressure to start car and by pumping the gas pedal the car is flooding itself and that let's it start.

YOU SAID IT GAS CAP WHAT YOU NEED.

P0171 indicates a lean condition. The most common cause of this is a defective mass air flow sensor. Also check if any vacuum leaks.Replace MAf sensor,if cleaning the MAF does not help.

Thanks.

go to http://edmunds.com put in the info of your vehicle then go to specs it will have all info you need

If the car is pinging you will set a knock sensor code.'
This comes from bad gas and running lean., You really need this professionally inspected to rule out the basics. I have seen alot of nissans with the knock sensor code stored but the light is still off.
Fill up the tank with high octane chevron and some techron injector cleaner and clear the light. If it stays off for a couple days then go get it inspected. Even if the code is stored it will still pass as long as the light is still off and the monitors have run.

Full sensor needs replacing it`s in the gas tank

This Was A Serious Fuel Leak ans the Tank MUST be Removed to Replace the Fuel lines

FUEL TANK, 17.2 Gallons/65 Liters