Audi S5 Wont Start After Fueling
 

I bought a 2008 S5 a couple weeks ago, and I've run int o an issue where the car will turn over but wont fire all the way after getting gas. This happens for a couple tries and then fires up fine, and never does it again until I get gas. I replaced the canister purge valve, but that didn't fix the problem. Does anyone know what else could be causing this? The car only has 41,500 miles on it.

Colton, check the Purge Vent valve. When these fail they give symptoms as yours. Also known as the N80 valve. I have a 2013 3.0t so I am not sure where (most likely engine bay) yours is located. Google search for a pic, all Audi ones look about the same, then look in your engine bay. Do you have Ross-Tech (Vagcom), it should tell if your N80 is throwing a code. Doesn't always set off the CEL if it is intermittent.

Might try a fuel pressure leakdown check. After you shut off the engine see how fast the fuel pressure drops. Should stay pretty high for a few hours.