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The first code you have P1491 is a evap code for the Vacuum Cut Valve ByPass Valve, See image. That could be giving you the gas smell if a Evap line is broken. I would inspect that plastic valve and have evap system checked. Vent control valves and evap canisters are some what common.I don't think gas was coming out of the exhaust, it may have been just condensation build up ( water ), that is common to drip from the tail pipe.
The running ruff and misfire code. There was a common problem with Nissans ignition coils. If you have a ignition primary code, that would indicate that all coils should be replace. I certain misfire code, you may be able to get away with just the one coil. I would see if you can get the code, so you can look into the cylinder that is misfiring.
If you have any more questions about this, please feel free to ask. Thanks
This does sound a bit strange. There is no way the Intake can suck the tank dry. The only other thought is maybe you have an injector or 2 stuck open, and is dumping fuel into the cylinder. I would remove the spark plugs and see if they are wet with fuel also. If they are, I would pull the fuel pump fuse and crank the car with the plugs out to try to dry out the cylinders.
If you have a stuck open injector, then the injectors would need to be check to find out witch one of them is stuck open, by ohming each injector.
The Evap Canister is located in the drivers side rear. Here are some images for you.
If the computer failed, it may not produce a code.
I will opt out an let another expert give you there opinion. Thanks and hope everything works out for you.