Evap issue (fuel pump at gas station keeps shutting off)

[vladvv]

Hello, I'm trying to figure out my evap issue

This is my 95 legacy automatic, with the charcoal canister under the hood

 

When I go to fill up at a gas station the pump always cuts off, and I can see fuel vapors pouring out of the filler if I move it back and fill up that way. I believe this tells me the line between gas tank and charcoal canister is clogged.

 

 

 

Diagnostic:

I took off the line going to tank from canister, and removed the 2-way valve  (Part 14)

I blew air into the tank bound line with a tire pump, and could feel air gently coming out of gas tank: so I guess this line is clear

I blew air into the charcoal canister and could feel air coming out the other line, so I assume canister is clear

 

Blowing air through the 2-way valve is very difficult, but I can (with my mouth...)

I suspect the 2-way valve, but I have no idea what it's supposed to act like. Looking through FSM I did not find any instructions on testing it. Can anyone tell me how this part should behave or how to test it?

 

 

 

 

[Bushwick]

Try a different gas station and see if it persists. Can also try not forcing the nozzle all the way into the filler hole, but rather just far enough in that it won't splash or fall out (the rubber accordion or round flap on the nozzle is to prevent splash back, not seal from the outside). Honestly, I don't think it's your car. Also, some gas station nozzles are super sensitive and don't exactly "work" as intended. I've run into some nozzles that constantly shut off over the years, and wasn't the car. Oh, I wouldn't pressurize your fuel tank again. All it'd take is static to ignite and you'd have a super bomb, not too mention the components might get damaged. It's usually under vacuum, not positive pressure. When you remove a "working" gas cap after the car has been running, that's a vacuum seal you are breaking. If you don't hear anything, your gas cap might need replaced. 

Edited October 30, 2013 by Bushwick

[vladvv]

Try a different gas station and see if it persists. Can also try not forcing the nozzle all the way into the filler hole, but rather just far enough in that it won't splash or fall out (the rubber accordion or round flap on the nozzle is to prevent splash back, not seal from the outside). Honestly, I don't think it's your car. Also, some gas station nozzles are super sensitive and don't exactly "work" as intended. I've run into some nozzles that constantly shut off over the years, and wasn't the car. Oh, I wouldn't pressurize your fuel tank again. All it'd take is static to ignite and you'd have a super bomb, not too mention the components might get damaged. It's usually under vacuum, not positive pressure. When you remove a "working" gas cap after the car has been running, that's a vacuum seal you are breaking. If you don't hear anything, your gas cap might need replaced. 

 

I had the gas cap off when I was running the pump, so there was no pressure. I am experiencing gas shut off at many stations, and when I pull it out so it does not stop I can see massive amounts of fuel vapors pouring out of the side of the filler. I'm surprised that the "two way valve" is a proprietary part, but there's no procedure in the FSM for cleaning/inspecting/diagnosing any issues with it. I think I'm going to try filling up without the valve installed and if there's a dramatic change assume that's it.

[Bushwick]

Read these 2 links as they may help you understand better what's happening.

 

This link is really good with illustrations and some ways to diagnose:

http://www.agcoauto.com/content/news/p2_articleid/242

 

 

This quick link shows how a gas nozzle works to understand better why it's shutting off:

http://auto.howstuffworks.com/fuel-efficiency/fuel-consumption/gas-pump-full-tank.htm

 

 

Also, no.14 is a 1-way check valve, not 2-way. So it should easily pass air through 1-way, while completely blocking air in the reverse direction.

[vladvv]

Read these 2 links as they may help you understand better what's happening.

 

This link is really good with illustrations and some ways to diagnose:

http://www.agcoauto.com/content/news/p2_articleid/242

 

 

This quick link shows how a gas nozzle works to understand better why it's shutting off:

http://auto.howstuffworks.com/fuel-efficiency/fuel-consumption/gas-pump-full-tank.htm

 

 

Also, no.14 is a 1-way check valve, not 2-way. So it should easily pass air through 1-way, while completely blocking air in the reverse direction.

Really? for some reason it's listed as "two-way valve" in parts lists and FSM... makes sense... the its purpose is to let the excess air pass from gas tank, but not back?

[Bushwick]

I honestly haven't looked at what ours run up close, but the diagram you linked is one-way and probably has a simple ball check valve with a spring keeping it seated (PCV systems run the same type, manual boost controllers work the same way). I know on newer cars (OBDII) it's electrically activated (pretty sure it's still an open/close affair unless there is a bypass or something, and can cause problems with drivability (and CEL) if it's "stuck" while the engine is running (speaking in general). If it was a true "2-way" valve (allowing flow in both directions) it'd have to be electrically controlled as I don't see how it'd be able to contain anything inside the canister as it'd flow right back to the tank, meaning how would it switch flow without a solenoid? Maybe their reference to "2-way" is just a name, I dunno maybe I'm wrong. Were those links helpful? If you check valve is sticking, you can try and liberally spray carb cleaner in it and see if it frees up. It most likely has a directional arrow on it to signify flow, so long as it's flowing in the correct direction it should be OK. But it's still possible it could sticking at times. 

[okamikai]

I'm having a similar issue with my Forester, but when I'm finally done putting gas the car will shut off right after I turn it on, as if the fuel line had emptied. After a few atempts it will rev up and down until it stabilizes, which takes around 2 mins total, still trying to figure it out...

[heartless]

I would just eliminate the check valve and see what happens. Just replace the line with a piece long enough to go from the block fitting to the canister. If that sloves the problem, then you know it is/was the check valve causing it.

 

none of the first gen, 90-91 Legacys (5) that we have had ever had that little check valve going to the charcoal canisters under the hood...has to be something that was added later for emissions purposes.

[Bushwick]

^ You can bypass the valve temporarily, but long term on cars designed to run with it can cause drivability issues, especially on OBDII cars. Best bet is to either clean it out, or replace, otherwise it can't store the fumes in the canister.

[vladvv]

I would just eliminate the check valve and see what happens. Just replace the line with a piece long enough to go from the block fitting to the canister. If that sloves the problem, then you know it is/was the check valve causing it.

 

none of the first gen, 90-91 Legacys (5) that we have had ever had that little check valve going to the charcoal canisters under the hood...has to be something that was added later for emissions purposes.

 

I actually did that yesterday. I inspected the valve and it does have an arrow on it. I can blow air easily in the reverse direction, and can blow air through in the direction of the arrow but only with a lot of force... I replaced the valve with a piece of hose and tried to fuel up, I didn't see fumes coming out by the filler and it did not click off so that must be the problem.

 

The part is like $50 from Subaru or something so I'm going to try to clean it with carb cleaner/air/etc (stuck ball or something?) If that doesn't help next time I go to junk yard I will pull a couple and play with them to see if they are passing air in the right direction.

 

I'm thinking the hose might be better than the defective valve since at least it passes air from tank to canister... I was considering actually flipping the valve but if there's dirt or stuff in there it's probably not the best idea.