Gas Nozzle Auto Shutoff - Triggers, but Splashes Gas

[Kibo]

I think the issue is that your fuel tank is pressurizing slightly while filling. When the fuel pump shuts off, the pressure "burps" out your filler tube. Your test of disconnecting the evap canister supports this--the excess air pressure from filling the tank was able to escape through this hose. However, it's meant to escape through the vent tube that runs alongside the filler neck to just below the fill cap. (The secondary line in this pic for reference



Have you checked this vent tube that to make sure it's clear all the way to the fuel tank?

Your fill tube configuration looks a bit different than mine, but this vent tube should run directly to the top of the tank (no check valves, tees, etc.).

By the way, here's a video explaining how the gas pump shutoff works:

https://www.youtube.com/watch?v=fT2KhJ8W-Kg

Long story short, the fuel level in your filler hose needs to cover the vent on the gas pump nozzle in order to shut off the flow of gas.

[motovan_mn]

Originally Posted by Kibo

I think the issue is that your fuel tank is pressurizing slightly while filling. When the fuel pump shuts off, the pressure "burps" out your filler tube. Your test of disconnecting the evap canister supports this--the excess air pressure from filling the tank was able to escape through this hose. However, it's meant to escape through the vent tube that runs alongside the filler neck to just below the fill cap. (The secondary line in this pic for reference



Have you checked this vent tube that to make sure it's clear all the way to the fuel tank?

Your fill tube configuration looks a bit different than mine, but this vent tube should run directly to the top of the tank (no check valves, tees, etc.).

By the way, here's a video explaining how the gas pump shutoff works:

Long story short, the fuel level in your filler hose needs to cover the vent on the gas pump nozzle in order to shut off the flow of gas.

Really appreciate the detailed response! I have not yet checked that the vent tube running parallel to the fill neck is clear. That video of the gas pump shutoff is the best i've seen yet - excellent explanation!

I kind of figured that a lot of the pressure buildup was intended to be relieved through the charcoal canister as well. My understanding is that the charcoal canister has two potential "outputs" - the purge vent and the atmospheric vent.

The purge vent is controlled by a normally closed solenoid, and the atmospheric vent is controlled by a normally open solenoid. So shouldn't the fuel tank be able to vent any pressure buildup through the charcoal canister? In any case, I will make sure the filler neck vent tube is clear and report back.

[moorefc]

So shouldn't the fuel tank be able to vent any pressure buildup through the charcoal canister?


That is what the cannister is for, driving pass-thru to the engine, parked filling, pass-thru the cannister to the atmosphere...Maybe I missed it earlier in the thread, but to troubleshoot the canister effect, you could disconnect its input and fill the tank....


I solved my shutoff issue finally after fixing some hosing crimp issues and not "seeing" issues with the canister, but replacing it...(I don't remember doing a fill tank disconnect canister test, but seemingly easily blew air thru it).



ebay eased the decision in my case..

[motovan_mn]

Originally Posted by moorefc

So shouldn't the fuel tank be able to vent any pressure buildup through the charcoal canister?


That is what the cannister is for, driving pass-thru to the engine, parked filling, pass-thru the cannister to the atmosphere...Maybe I missed it earlier in the thread, but to troubleshoot the canister effect, you could disconnect its input and fill the tank....


I solved my shutoff issue finally after fixing some hosing crimp issues and not "seeing" issues with the canister, but replacing it...(I don't remember doing a fill tank disconnect canister test, but seemingly easily blew air thru it).

I just verified that the fill neck vent tube is clear, so now I guess I will pull the trigger on a new canister. Fingers crossed!



ebay eased the decision in my case..

Yep, I tried filling the tank with the charcoal canister disconnected, and that seemed to solve both problems (auto shutoff engaging every few seconds, and gas splashing out of the fill neck once the tank was full).

However, I reconnected the charcoal canister after making sure all the passageways were clear, and the first issue (auto shutoff every few seconds) magically went away, but the splashback issue remained.

[motovan_mn]

I bit the bullet and purchased a new charcoal canister, despite none of my tests on the old canister indicating that it was bad. Disappointingly (but not surprisingly), the new charcoal canister did not solve the splashback issue either.

So the current state of the situation is as follows:

• I can fill the tank completely at full speed without the auto-shutoff triggering early/multiple times
• When the auto-shutoff triggers at the end of the fillup, a little bit of gas "dribbles" out. This is an improvement over the original problem, where gas was "splashing" out.

I believe the splashback issue was significantly improved by removing some kinks I found in the vent hoses coming out of the fuel tank (see previous posts).

Additionally, disconnecting the charcoal canister entirely solved the splashback issue completely, so I'm inclined to believe this is still some sort of venting problem. Will continue digging...

[Nathandeuel]

We had a similar issue with our 2015 Chevy. I tried various things but what seems to have finally fixed it? We replaced the whole dang fuel tank. I do not want to say how much it costs, as I am still traumatized. We finally bit the bullet because we started throwing evap codes. I could deal with pumping gas being a nightmare but a check engine light was a bridge too far.

[motovan_mn]

Originally Posted by Nathandeuel

We had a similar issue with our 2015 Chevy. I tried various things but what seems to have finally fixed it? We replaced the whole dang fuel tank. I do not want to say how much it costs, as I am still traumatized. We finally bit the bullet because we started throwing evap codes. I could deal with pumping gas being a nightmare but a check engine light was a bridge too far.

Oof, don't scare me like that!

[Nathandeuel]

I'm sorry! I bought the van June 2020 for a crazy cheap price and when I went to fill it up I realized why: couldn't pump fuel without shutoff. For two years I ignored it, even in Wyoming for instance when it was like -20 and it took me 15 minutes to fill up. But I gotta smog that big dumb van in Cali so I went nuclear. Hope your fix is much easier!

[moorefc]

Originally Posted by motovan_mn

I believe the splashback issue was significantly improved by removing some kinks I found in the vent hoses coming out of the fuel tank (see previous posts).

Additionally, disconnecting the charcoal canister entirely solved the splashback issue completely, so I'm inclined to believe this is still some sort of venting problem. Will continue digging...

It sounds like you have checked the CVS canister vent solenoid and line with engine off?


These might give you some additional ideas...
https://www.ford-trucks.com/forums/1...-problems.html

https://www.motor.com/magazine-summary/fords-evap-system-operation-testing/

[motovan_mn]

Originally Posted by moorefc

It sounds like you have checked the CVS canister vent solenoid and line with engine off?


These might give you some additional ideas...
https://www.ford-trucks.com/forums/1...-problems.html

https://www.motor.com/magazine-summary/fords-evap-system-operation-testing/

I actually haven't tested the canister vent solenoid by applying 12V to the connector. However, since the solenoid is built into the canister, replacing the charcoal canister should have ruled that one out. But probably worth testing the new one anyway.

And just to be clear, are you suggesting that the solenoid might have failed in the closed position, thus not allowing the canister to vent to atmosphere?