lots of gas vapor from vent hole next to gas cap

[ericmuscle]

not sure whats going on here. there is also wet fuel covering the inside of the compartment where the gas cap is. and gas moisture where the vent hole is next to gas cap. i have a return fuel system. just replace the gas cap and still no fix. i looked inside my trunk and i see the hose that vents inside the gas cap compartment. can i clamp that hose, i know the tank wont vent then, but what other options are there?

the gas vapor seems to appear after driving for about 20-30 min.

whats the problem and where/how do i fix it or start troubleshooting?

2003 mustang cobra with 1000hp lethal performance return fuel system

 

[MG0h3]

I just switched to return and had the same thing going on. Thought for sure that I had left something unhooked or maybe cut an extra wire when splicing the sender in. Nope. Even replaced my gas cap too...until I saw the residue coming out of the vent.

Never changed anything but it went away. I believe it was from doing datalogging/tuning. Car was in open loop the whole time and EVAP disabled? Not totally sure but its the only explanation.

That line runs over to the canister thats up by the drivers rear wheel. Make sure both of those connections got hooked up over there.

 

[ericmuscle]

what would happen if i clamped that hose that leads to the vent? all my evap hoses seem to be all hooked up.

 

[MG0h3]

Dont do that. Are you sure EVAP isnt turned off and who did the tuning?

How wet is it near the vent opening near the cap? Mine was just a very small area of wetness that would be caused by a drop or two of fuel.

Did you blow out or remove the old fuel line as well? It will be full of gas and can cause a smell.

 

[ericmuscle]

Dont do that. Are you sure EVAP isnt turned off and who did the tuning?

How wet is it near the vent opening near the cap? Mine was just a very small area of wetness that would be caused by a drop or two of fuel.

Did you blow out or remove the old fuel line as well? It will be full of gas and can cause a smell.

i have to check with my tuner and see if he's turned off my evap......why would a tuner turn off the evap?

i can see fuel moisture covering the wall between the gas cap and vent hole and see a drop of fuel that ran down the wall and settled under the gas cap.

i havent been noticing any fuel smell till recently. i do see what appears to be the charcoal canister behind the drivers side rear wheel and what appears to be some solenoid that may open or close to allow gas vapor to pass through, is there a way to bypass that solenoid to have the vapor pass through the charcoal canister at all times, just wondering if the solenoidvalve is bad.

 

[MG0h3]

Ok to confirm, are you done tuning? I was doing it remote and had the fuel smell the entire time.

If your evap system isnt working right, you should get a code.

If you didnt have the smell right after going to return, you better double check for some leaks. I can still see the little residue from the vent (never cleaned it) so its possible youre just seeing it and smelling fuel from a leak.

 

[ericmuscle]

Ok to confirm, are you done tuning? I was doing it remote and had the fuel smell the entire time.

If your evap system isnt working right, you should get a code.

If you didnt have the smell right after going to return, you better double check for some leaks. I can still see the little residue from the vent (never cleaned it) so its possible youre just seeing it and smelling fuel from a leak.

car is done being tuned. iv always had the smell..i dont drive the car for long trips, but when i do i start smelling gas vapors and its definitely coming from the vent hole by the gas cap. there is definitely no gas leaks and im not getting any codes.........after doing lots of reading i read from others that with their return fuel system after driving for 20-45min the gas that is returned to the tank is alot hotter from the engine and is heating up the fuel in the tank, fuel pumps are getting hotter,etc and causing the gas to emit vapors.............not sure how to fix the problem...possibly place an inline charcoal canister in the vent line? or something like this https://www.iimuch.com/collections/fuel-differential-vents/products/fuelvent2

 

[MG0h3]

Mine is deadhead so the return fuel doesnt make it to the engine. Many older setups had the reg right on the rail and we didnt have fuel smell problems then so I dont think thats the problem.

I suspect something got changed in the tune or when you did the return system.

You sure you blew out the original fuel line??? I used compressed air, brake cleaner, compressed air a few times.

 

[ericmuscle]

Mine is deadhead so the return fuel doesnt make it to the engine. Many older setups had the reg right on the rail and we didnt have fuel smell problems then so I dont think thats the problem.

I suspect something got changed in the tune or when you did the return system.

You sure you blew out the original fuel line??? I used compressed air, brake cleaner, compressed air a few times.

the gas vapor and residue is definitely coming from the vent hole in the gas cap compartment, so blowing out the original lines isnt gonna help....why would that vent line always emit gas fumes after car is running for awhile? i thought all the pressure and fumes leave the tank via evap system and if thats the case then why is there a vent in the gas cap compartment....im still learning

 

[MG0h3]

I read up on it briefly and cant remember all the tech stuff. The canister gets purged only at certain times when conditions are met. Once that can is saturated, it cant hold anymore vapors or it basically turns into a bomb, hence the vent. When the system actually does operate, the vent is also there so that the tank isnt put under a vacuum.

Its possible that heat is the problem, but Ive lived in 115* temps and not had a problem.

If this started right after going return and a new tune, I really think thats where the problem is.

I didnt track down all the wires/solenoids on top of the tank but I initially thought that might have left something unhooked. Id check that for yours as well.

 

[mbsvt]

The Evaporative Emission (EVAP) system prevents fuel vapor build-up in the sealed fuel tank. Fuel vapors trapped in the sealed tank are vented through the vapor valve assembly on top of the tank. The vapors leave the valve assembly through a single vapor line and continue to the EVAP canister for storage until the vapors are purged to the engine for burning.

If the evap system is turned off in the tune, then it is possible the stored vapor fume have saturated the carbon canister and that's why your smelling it from the vent tube.
Just a thought!!
MB