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Need help! I almost figured out my fuel tank problem...

Okay guys, so today was the day I started to tackle the problem with fueling my Boxster (after three summers). I always thought it was the slipped tube flapper problem and didnt want to deal with it. It wasnt the problem. My filler tube is shrouded by a plastic tube in the tank and is not in contact with anything. It free flows from the filler all the way into the tank.
So, that means a vent problem...
The attached photo shows the top of the sending unit. My finger is pointing to the vent. I took the unit out and was unable to blow in or out (I know its a one way). My question is, does that mean that its bad, or are there electronics involved? Im trying to find out if this part is bad regardless if it's plugged in or not to the system. I would think that I should be able to suck air through it...
(I was able to blow through the tube attached to it on the outside by the way.)
Any help is VERY appreciated!

Old 07-31-2011, 06:00 AM
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I think the vent is electrically controlled. If you push the flapper in a magnetic switch closes and the vent valve at the tank opens. Porsche has a unit up near the filler opening they call a vent valve. This is a picture of mine removed from the car.



If this unit isn't working you'll have trouble filling. Also the magnetic switch. A new one comes with a new vent valve.



If you can get the tank to fill by depressing the little tab where the side of the filler cap presses down when you thread it back down, then the magnetic switch could be the problem. That's what happened to me when I replaced the valve in the picture and didn't put the switch back where it's supposed to go, which is actually a recess on the side of the plastic valve. I couldn't get a half a gallon of gas to go into the tank. It worked before I took it apart so I knew it was something I did and was able to figure out what I'd done wrong. You might have a different problem than I did. I actually have an extra magnetic switch if you need it.

I had all the charcoal stuff apart at the same time and I couldn't blow through any of the lines that went back into the tank.

Last edited by Dale_K; 08-01-2011 at 11:52 AM..
Old 08-01-2011, 11:49 AM
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Thanks for the reply Dale...
I have a 2000. I heard that the solenoid flapper was on 2001+
What year do you have?
I'm not sure that is the problem. While I was in the tank I had my brother blow through a hose at the filler flap and I was able to see the air coming out the tank side of the filler tube. There is a plastice shroud that fits over the end of the filler tube and bends down towards the tank. It's not what I was expecting to see. I was under the impression that the filler tube was just exposed in the tank and had a flap. I suppose I should take the plastic shroud off and see if there is any kind of flapper at the tank end of the filler tube. If the problem is not there it has to be somewhere in the evap tubing or valves.
Man, I have some work cut out for me
Old 08-02-2011, 04:45 AM
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How far down the filler tube is that other magnetically controlled flap? Is it where the tape is?
Old 08-02-2011, 04:47 AM
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My car is a 2000 S. The magnetic switch actually fits inside a cavity on the side of the plastic vent valve housing where it lives pressed against the fill tube in the right spot to detect the flapper. The whole vent valve just clamps around the fill pipe up at the fuel door. When I finally got my vent valve and switch back together correctly I could hear a faint click and hear the tank breath out when I pressed the flapper back with my finger.

I haven't seen the filler tube in the tank but I've read a technical article that says there is a "spit back" valve on the fill tube. I think it keeps fuel from splashing out when the tank gets full. Here's a screen shot of a diagram I found.


Last edited by Dale_K; 08-02-2011 at 12:32 PM..
Old 08-02-2011, 12:24 PM
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Dale, thanks for the info. I guess from here I need to remove that plastic vent valve housing and see what might be going on with it. I've checked the fuse so many times I know that's not the problem. Not sure how a simple magnetic switch could malfunction... But I guess I need to check it out! Maybe some connectors/wires got loose?
Old 08-02-2011, 07:46 PM
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This is interesting stuff. My 2001 Boxster S has a problem where it builds up pressure in the fuel tank that never gets released - I did not realize there were these magnets and stuff in the venting system. Maybe this is where my problem is as well?
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Old 08-02-2011, 09:38 PM
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I wonder if there's a way to bench test this part? I guess by simply blowing through it... but as far as the magnet... that's probably going to be more of a visual inspection and how it's positioned etc...
Old 08-03-2011, 04:44 AM
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The diagnostic test for whether it's the plastic vent valve gizmo up near the filler pipe door is to depress the little tab on the edge of the filler opening ring. I don't have my car right now so I can't take a picture but it's the part that the edge of the gas cap depresses when you screw it down. The little tab moves down about half an inch and moves the valve into a position where you can get gas into the tank even if the magnetic switch is not working. This isn't how the valve works in regular use but it's a work around for a tank you can't fill. You'll need a small screwdriver to press down in the same spot the edge of the gas cap would normally hit.

If you can get it to take gas when you depress the tab but it won't take gas otherwise it might be the magnetic switch (assuming the fuse is good). On my car the magnetic switch wasn't where it needed to be because I worked on the vent valve and didn't put it back correctly. A new vent valve comes with a new magnetic switch. It doesn't cost very much and it's not too hard to replace once you've removed the right front fender liner. The plastic valve just clamps around the filler tube and one bolt holds it in place at the fuel door. You have pretty much total access to the charcoal cannister, the tubes that connect the venting system to the cannister and the valve block behind the right side headlight. That valve block has two small electricly operated valves. One is spring loaded open and the other is spring loaded closed. The car's computer cycles those valves in various ways when it does an emissions check on the fuel tank and during normal driving. The Durametric can cycle the valves for testing and you can hear them clicking.

I'm not an expert on Boxsters - I'm just telling you what I found out when I worked on my car. Your car might have a different problem.
Old 08-03-2011, 09:49 AM
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Thanks a tome Dale! Your help gives me an excellent starting point to diagnose the rest of the evap system! I'll let you know what I find out! I was going to work on it this weekend, but having this information motivates me to work on it tonight after work!
Old 08-03-2011, 10:29 AM
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Well, all of the valves seem to be working. I looked at the magnetic switch thats in the filler vent valve and from what I can tell it looked to be okay. It was clean and all of the connections looked good. So my guess is that the spit back valve in the filler tube down the line must be stuck or not working because I do not hear the "click" so many people talk about when the gas nozzle valve is opened. I wish this were easy. Looks like I'll need to go back into the tank again and figure out how to resolve this from that end
Old 08-08-2011, 04:54 PM
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Maybe you could tap that fuel level limit valve, marked as #3 on that diagram. It looks like a float valve that cuts off venting when the valve rises. If the ball float was stuck in the up position it might make it impossible to vent the air in the tank. This is 100% a guess on my part. I know that sometimes my car won't let me fill above 3/4 of a tank and other times it works fine.

Another thing that happened on my car after I drove around for about a month without the fender liner installed. The wires controlling the charcoal cannister valves fell down and the tire rubbed through them, eventually setting a CEL. After I fixed the wires filling the tank to the top became much easier. I could set the gas station nozzles as fast as it would go and the car would accept gas to match. It also began taking gas beyond the 3/4 full level. I remember reading a post by somebody who said they cured their filling problem by driving the car around very violently and sloshing the gas in the tank very massively. I don't know if these will do you any good.

I have an extra brand new magnetic switch you can have if you want. Send me a PM and I'll mail it to you.
Old 08-09-2011, 04:34 AM
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Dale regarding that diagram... In my tank the vent valve is part of the sending unit. There's some type of a ballbearing valve in the tank. It didn't seem like it was working well when I inspected it. I messed around with it and felt like I had somehow fixed it. Still was unable to fill the tank.

Since I do not hear the click when I open the filler flap it's probably the switch, a closed spit back valve down the filler tube or the solenoid that controls that second flap (spit back valve) if it's that then boy do I have some work
Old 08-09-2011, 06:19 PM
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Just wondering something before I get back into my car.
If my fuel door lock is not working anymore... would that have anything to do with the tank fill problem I'm having? Or is that solenoid strickly for locking the fuel door? I'm wondering is it controlls anything else back there.
Old 08-13-2011, 10:47 AM
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vent valve magnetic switch

Quote:
Originally Posted by Dale_K View Post
I think the vent is electrically controlled. If you push the flapper in a magnetic switch closes and the vent valve at the tank opens. Porsche has a unit up near the filler opening they call a vent valve. This is a picture of mine removed from the car.



If this unit isn't working you'll have trouble filling. Also the magnetic switch. A new one comes with a new vent valve.



If you can get the tank to fill by depressing the little tab where the side of the filler cap presses down when you thread it back down, then the magnetic switch could be the problem. That's what happened to me when I replaced the valve in the picture and didn't put the switch back where it's supposed to go, which is actually a recess on the side of the plastic valve. I couldn't get a half a gallon of gas to go into the tank. It worked before I took it apart so I knew it was something I did and was able to figure out what I'd done wrong. You might have a different problem than I did. I actually have an extra magnetic switch if you need it.

I had all the charcoal stuff apart at the same time and I couldn't blow through any of the lines that went back into the tank.
Dale - I recently had the vent valve replaced on my 2000 Boxster and now cannot add gas. My new vent valve did NOT come with a new magnetic switch. Do you know where I can order one? Can't seem to find it on the pelican part website. Thanks!
Old 10-18-2014, 10:36 PM
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