How can I determine which pump is going out? the left or right side pump. The car stumbles when you give it the gas and then will stop running if you get out and bang on the tank from under the car it starts up again and runs fine for a few miles or so enough to get you back home.

 

One question real quick. When was the last time (if ever) that the Fuel filter was replaced? Sounds crazy, I know.. but both of my TTs that I've had were both using the ORIGINAL fuel filter and changing that one component made the difference between my car dying on the interstate and driving across 3 states.