Gas cap hissing. Can barely pump gas.

iboughtatahoe23 · Jan 30, 2025

2014 Tahoe Lt 178k

Changed charcoal canister. And now it’s worse. Don’t know how pellets would have gotten in the lines if I took the hoses off before the canister. Any way. This thing clicks off every few dollars and hisses when I take off the cap. I have to trickle it or use a funnel.

Some youtube videos below:
1) Gas cap hiss
2) Pump clicking off

PPV_2018 · Jan 30, 2025

Sounds to me like possible fuel vapor issue? Did you purge the lines out when you took them off to replace the charcoal canister

Had a similar issue on a different car where the evap purge solenoid failed choked the fuel system.

Fless · Jan 30, 2025

If the ignition is in the off position (meaning no power to the evap system) either the canister vent valve is not opening or the evap system is somehow plugged. The system shouldn't hold pressure like that with the ignition off.

Here's some of the back story: https://www.tahoeyukonforum.com/threads/charcoal-canister.152136/#post-1935228

Joseph Garcia · Jan 31, 2025

Hopefully, you remove the gas pump at the first click, when filling your tank (prior to this issue). Most canister/pellet issues arise when folks try to top off their gas tanks with successive gas pump clicks after the first one.

iboughtatahoe23 · Jan 31, 2025

Joseph Garcia said:
Hopefully, you remove the gas pump at the first click, when filling your tank (prior to this issue). Most canister/pellet issues arise when folks try to top off their gas tanks with successive gas pump clicks after the first one.

There has been times where I got frustrated and have done this but nine times out of 10 when it clicks off, I’ll let it go back down and then repeat

iboughtatahoe23 · Jan 31, 2025

Fless said:
If the ignition is in the off position (meaning no power to the evap system) either the canister vent valve is not opening or the evap system is somehow plugged. The system shouldn't hold pressure like that with the ignition off.

Here's some of the back story: https://www.tahoeyukonforum.com/threads/charcoal-canister.152136/#post-1935228

I noticed it only hisses when the vehicle is on, when I’m filling out the pump and it doesn’t matter if the vehicle is on or off it always clicks off after a few bucks.

iboughtatahoe23 · Jan 31, 2025

PPV_2018 said:
Sounds to me like possible fuel vapor issue? Did you purge the lines out when you took them off to replace the charcoal canister

Had a similar issue on a different car where the evap purge solenoid failed choked the fuel system.

Yeah, I can’t figure it out and it’s starting to look like the only option is going to be dropping the tank and blowing the lines out which I really don’t wanna do so I’m gonna take it in

Like I said, no idea how the pellets went down the tubes if I took the tubes off before

tuckerrnr1 · Jan 31, 2025

When I replaced my canister, while the lines were still disconnected, I blew air into the tank from the filler neck to clean out the lines. I just used an air nozzle and a rag to seal the filler tube. Quite a bit of charcoal came out without having to drop the tank.

Fless · Jan 31, 2025

It's not whether or not the canister was disconnected, the canister can dump charcoal pellets into the lines any time it gets internally compromised. It's probably been leaking them out for a while.

I can't tell -- when it's hissing is it blowing out fumes or sucking in air?

iboughtatahoe23 · Feb 1, 2025

Fless said:
It's not whether or not the canister was disconnected, the canister can dump charcoal pellets into the lines any time it gets internally compromised. It's probably been leaking them out for a while.

I can't tell -- when it's hissing is it blowing out fumes or sucking in air?

I believe it is sucking air in. Like the tank is depressurized.

Gas cap hissing. Can barely pump gas.

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