Car_Fynatik

00 S4 Tip, with a small vac leak.
DTC code specifies a small EVAP leak, which my boost gauge confirms.
I have literally tested EVERY vac line in the car, and there is only one thing I can find causing the leak, the gas tank.

This is a picture of where the charcoal canister sits, and the 3 lines that connect to it.


#1 connects to the LDP, it is one of the 2 vac lines the LDP uses to test for leaks. This line is intact, LDP is intact, & line from LDP to vac canister up front is intact.

#2 connects to the gas filler neck, this is where the fuel vapor is introduced to the charcoal canister. With vac pump on this line the max I get is -11" vac, telling me the leak is there somewhere. I get the same results with & without the gas cap on, so thats not the issue.
I am stumped about this leak for the time being.

#3 connects to the N80 purge valve on top of the engine. Line holds full vac, and purge valve is working fine. No issues here.


My idea is to cap line #1 & #3, eliminating the vac leak & the car should think all is copacetic.
Leave line #2 connected to the canister so fill ups wont be an issue & the canister will still trap fuel vapors as intended.


Feedback? Possible issues? Ideas about the leak?

Car_Fynatik

Boost gauge also confirms the gas tank leak, as at idle I see a max vac of -11", identical to what I see with the vac pump under the car when connected to that system completely isolated from everything else.