Gas Fuel Gas Cap no Hiss

[azkkr]

96 TSI

Whenever I open my gas cap, I never get a "HISS" or pressure release from the tank. I heard, I am supposed to but, I never get this "SOUND", neither with full tank nor empty.

Is this normal?

 

[90 Eagle Talon]

I think it depends on how hot it is when you fill up, if you leave you car to bake and then go open it I guess it should but if you fill at night when it is colder it probably will not at least it is like that here in florida it is hot down here.

 

[DGajre777]

The 'HISS' sound will come from a pre-vent/vented gas cap. If you don't have a vented gas cap, you won't get that sound since it doesn't release fuel vapors prior to being opened. My Talon didn't have a vented gas cap.

http://www.stant.com/brochure.cfm?brochure=201&location_id=170

 

[azkkr]

The 'HISS' sound will come from a pre-vent/vented gas cap. If you don't have a vented gas cap, you won't get that sound since it doesn't release fuel vapors prior to being opened. My Talon didn't have a vented gas cap.

http://www.stant.com/brochure.cfm?brochure=201&location_id=170

I bought a regular cap last weeK. I do not think is pre-vented. I am asking because I am trying to fix a problem with the evap circuit. I check the voltage on the ecu to see if the Canister selonoid for the Evap was being grounded. The Volt reads about 13 V but never ground(never goes to 0). I got another ECU thinking that was the problem, but same thing happens. I am getting a P0446. I check all the vacuum lines, the canister, replace the solenoid and the purge valve, the ECU but still get the code. Therefore, I thought that maybe I have a vapor leak form the tank or the hoses but everything looks OK. No small of gasoline anywhere.

 

[DSM90AWD]

I assume you also checked the evap line comming in from the tank and the checkvalve?

 

[romeen]

I am having the same problem with no pressure buildup whatsoever in the tank as well as a P0455 code. This thread was very helpful to me.

http://www.dsmtuners.com/forums/showthread.php?t=259430

I ended up pressurizing my fuel tank via an air compressor hooked up to the EVAP line (where it comes into the engine bay) and listening for the leak. It turns out that I have a vacuum line (about 1" diameter) on top of the fuel tank at the rear that is disconnected. As fast as my helper could pump air in I could feel it rushing out of here. Since it's on top of the tank I couldn't visualize or even feel where it is supposed to be connected to. So next week I will have to drop the tank for this otherwise simple fix.

This may also help. Post #7 shows a good schematic (compliments of luv2rallye):

http://www.dsmtuners.com/forums/showthread.php?t=259173

 

[forged_tsi]

i have a similar problem where i have no hiss.. however i removed my emissions including blocked off egr.. i think i may need to cap something off for the evap canister.. ? could this be causing the problem? also im getting horrible mpgs since emissions were removed.. i didnt pay attention if there was a hiss prior..

also, when i was searching for a mysterious wet carpet cause.. i found gas under my rear seat.. and the plug was missing.. if i fill up and top it off i get a gas smell.. could a line be busted on top of my tank as well? maybe the previous owner had it out for some reason. i have no idea..

its a 91 talon TSI FWD btw..