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I know this has been covered, but all the posts seem to start with a direction to 'read the posts', which is less than helpful. 

 

I have the apparently common problem whereby I need to use a teaspoon when I fill my '01 996, or it will petulantly spit its breakfast all over my shoes.   

 

The car has done this since I brought it back to life last fall.  I have replaced the fuel line vent valve, checked the mythical E6 fuse (not sure what it does or what it powers, but mine seems the picture of health).  I cleaned a ground spade connector which connects to the alloy bracket which secures the fuel line vent valve to the fuller neck. I have also pulled the battery and tank cover plate (when I installed a new fuel pump earlier this week), all the hoses seem good (no mice) and properly connected with a 'click'.  From what I can tell, the fuel tank vents through a small diameter hose which connects to the vent valve via a canister. It appears that the air displaced by incoming fuel has nowhere to go; something in this Rube Goldberg Porsche design has gone awry, or never worked from inception. 

 

Apparently there is a factory bulletin on this issue?  Is there a number / date for it, or is there an online source for these?

 

The fuel line vent valve is a purely mechanical thing?  It seems to have no place to plug any wire in to it, so I am not sure how it decides to open or close. 

 

Thanks to all for any insight which you can share. 

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7 hours ago, johnmh said:
I know this has been covered, but all the posts seem to start with a direction to 'read the posts', which is less than helpful. 
 
I have the apparently common problem whereby I need to use a teaspoon when I fill my '01 996, or it will petulantly spit its breakfast all over my shoes.   
 
The car has done this since I brought it back to life last fall.  I have replaced the fuel line vent valve, checked the mythical E6 fuse (not sure what it does or what it powers, but mine seems the picture of health).  I cleaned a ground spade connector which connects to the alloy bracket which secures the fuel line vent valve to the fuller neck. I have also pulled the battery and tank cover plate (when I installed a new fuel pump earlier this week), all the hoses seem good (no mice) and properly connected with a 'click'.  From what I can tell, the fuel tank vents through a small diameter hose which connects to the vent valve via a canister. It appears that the air displaced by incoming fuel has nowhere to go; something in this Rube Goldberg Porsche design has gone awry, or never worked from inception. 
 
Apparently there is a factory bulletin on this issue?  Is there a number / date for it, or is there an online source for these?
 
The fuel line vent valve is a purely mechanical thing?  It seems to have no place to plug any wire in to it, so I am not sure how it decides to open or close. 
 
Thanks to all for any insight which you can share. 
 

Check to see if the Reed switch is in place. It is a sensor that is activated when a gas station fuel pump nozzle is inserted in the filler neck. 1499553701-10104.jpg

Sent from my Pixel 2 XL using Tapatalk
 

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Where would it be? (It does not look familiar).  I open the fuel cap, look in, I see a metal disk with a hole covered with a flap on a spring. Not much else.

 

When I fill it with a funnel and a gas can, it fills fine (albeit slowly).

 

Thanks.   

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Where would it be? (It does not look familiar).  I open the fuel cap, look in, I see a metal disk with a hole covered with a flap on a spring. Not much else.
 
When I fill it with a funnel and a gas can, it fills fine (albeit slowly).
 
Thanks.   
It is attached to the side of the vent valve.

Sent from my Pixel 2 XL using Tapatalk

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It is attached to the side of the vent valve.

Sent from my Pixel 2 XL using Tapatalk

See attachment photo1499553552-23172.jpg

Sent from my Pixel 2 XL using Tapatalk

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See attachment photo1499553552-23172.jpg.915ec2c26bbee06400f35aabcdbae915.jpg

Sent from my Pixel 2 XL using Tapatalk

See photo where Reed switch is attached to vent valve.db1b80605cfca858a71922d55db3ebc4.jpg

Sent from my Pixel 2 XL using Tapatalk

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I know you've looked at the posts and checked your hoses, etc., but take a look at the wires on the top of the gas tank that go to a gas tank vacuum switch.

Sure sounds like a switch is not opening to release pressure in the gas tank.  Yes, I was the "mouse nest" guy that learned about this little switch the hard way.

Others have mentioned that 996 cars do tend to fill very slowly, esp as the tank gets full.  So a bit of gas overflow is not unexpected.  Your issue as described is more than the usual situation.

Good luck.  Post up when you find the answer.

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Ah! That little cylindrical thingy connects to the gas tank vacuum switch where it pokes out of the vent valve.  Mine is not connected, and was not connected when I examined it before I replaced it.  That might be it. 

 

Thanks! Something to try this weekend. 

 

 

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Hope you have solved this mystery.  Curious to know the answer.

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Will have a chance to look at it on Thursday after work.  Fingers crossed.

 

 

 

 

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So, the small magnetic sensor was placed back into the groove in the plastic part of the vent valve which attaches to the fuel filler pipe.  Next trip to the gas station - no joy.  The fuel spat back out as usual.  This morning I unplugged the magnetic sensor and checked it with an ohmmeter - full resistance.  I then pushed a large diameter socket extension into the filler neck (to approximate a fuel filler nozzle).  Full resistance.  I then pulled the sensor from the car and bench tested it by placing it on a large chunk of steel.  Full resistance.  Finally, I placed a magnet on it - finally, the resistance dropped to near zero. 

 

Am I bench testing it properly?  Is it supposed to detect the presence of a steel gas station filler nozzle when placed into the fuel tank filler pipe?  

 

So far I have replaced the vent valve and the gas cap without luck.  I have also checked the fittings at the top of the tank.  Besides the vent for the charcoal canister, I am running out of options. 

 

Thank for the help so far, I would not have diagnosed the issue to this extent without help from this site. 

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High resistance may indicate that there is an internal short in the sensor, the ohms readings should be relatively low.

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45 minutes ago, JFP in PA said:

High resistance may indicate that there is an internal short in the sensor, the ohms readings should be relatively low.

Does it not need to be near something like a gas nozzle (i.e. steel) to close the circuit and open the vent?  

 

When it is just sitting on the (wooden) table, the resistance is infinite. Only when I press it against a magnet does the resistance approach zero.  I would have thought there was a magnet in it, i.e. when it senses the pump nozzle it closes the circuit and allows air to leave the tank (via the charcoal canister). 

 

I am beginning to understand why they redesigned this system on the 997.  Only Porsche could so overengineer what is effectively a hole to pour a liquid through. 

 

 

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13 minutes ago, johnmh said:

Does it not need to be near something like a gas nozzle (i.e. steel) to close the circuit and open the vent?  

 

When it is just sitting on the (wooden) table, the resistance is infinite. Only when I press it against a magnet does the resistance approach zero.  I would have thought there was a magnet in it, i.e. when it senses the pump nozzle it closes the circuit and allows air to leave the tank (via the charcoal canister). 

 

I am beginning to understand why they redesigned this system on the 997.  Only Porsche could so overengineer what is effectively a hole to pour a liquid through. 

 

 

 

Think about it: I have never seen a gas pump nozzle with a magnet on or in it.  If it needs a magnet to do anything, something is wrong with it...

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