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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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Just to update, so far I have replaced the vent valve, gas cap and sensor.  I have checked the E6 fuse.  Still no relief, the car continues to spit fuel when I try to fill it. 

 

My thoughts now go to the electric vent valve on top of the tank.  With the plug connector to that electric valve disconnected (and the battery connected to the car via jumper cables) i checked for voltage with the gas cap open and a large steel rod in the filler neck (to replicate the gas filler nozzle for the purpose of the sensor). No voltage comes from any of the three wires (which should be needed to open the valve on top of the tank, no?)  As mentioned, the E6 fuse seems fine. 

 

All I can think of is to check for continuity between the fuse box and the plug.

 

Any other ideas? No obvious rodent issues seem to exist. 

 

 

 

 

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Does anyone know how to access the fuel tank vent valve Pierburg  996.605.203.01?, I think it is on top of the fuel tank, but must the tank be removed (how?) to access it?  It seems to be the only part I have not replaced on the way to solving my fuel fill issue.

 

A picture may be found at:

 

https://www.carid.com/pierburg/carbon-canister-fuel-tank-vapor-valve-mpn-996-605-203-01.html

 

Thanks for any suggestions. 

 

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Posted (edited)

I recall that you take out the battery and remove the battery tray, and that the valve is right on top of the fuel tank.

I had to do this due to a mouse nest and nibbled wire in this exact location.  Great inde shop started top down when I was having your gas issue.

There's a thread on the forum about this.

He had to reconnect a chewed through wire and voila problem solved.  Must tell you the wire was cheap, but the time spent on the actually job did not come cheap.

Good luck...

Edited by judgejon

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I think the one on top of the tank is only a pressure sensor.  From what I can see in the Bentley manual, the actual valve that opens when you fill the car is somewhere behind the carbon canister inside the right fender.   Will explore further, but if this does not fix it, I am going to weld the fuel filler door shut, drill a big hole in the hood and the tank and put a racing fuel cap in the middle of the hood. 

  • Haha 1

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I bet your right about the sensor being on top of the gas tank.  Good luck with all this.  With the racing fuel cap and a big tank you will  soon be running full out at Thunderhill.  

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After taking out the fender liner for the 6th time, I realize I cannot remove the carbon canister to look for a valve behind it, there is apparently a mystery bolt which I cannot find.  I also cannot find the electrically operated valve which opens and closes the hose which releases pressure from the fuel tank to check and possibly replace it.  There are apparently three vent / shut off valves which make up the system, but they are very well hidden.  

 

This hopeless complexity is why I have resigned myself to take it to the dealer, as the agony of having to remember to bring a book to read when filling fuel into this thing exceeds (barely) what will certainly be the agony of ordering, locating and replacing these valves, just to learn (as with all the other things I have replaced so far at great expense) that none of them is actually the problem.  Geez, replacing the IMS bearing, AOS and clutch was far easier than this. 

 

Yes, I am frustrated, but feel better now that my rant is over.  

 

Did I mention that my F-car refuels quickly (albeit too frequently) by simply pouring super unleaded into a big hole in its side?  

 

  

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I understand your frustration and empathize.  Sometimes it helps to look at the parts diagram to see what you are dealing with.  Here is one of the carbon canister and apparently the one nut that holds it in...I think, but I've never been in there http://www.autoatlanta.com/porsche-parts/hardparts.php?dir=996-99-05&section=201-20

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Posted (edited)

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Principle 1: Understand the question before looking for the answer.

Principle 2: Start at the top and work down.

Were these valves/switchs already replaced earlier in the process?

If not, ...

 

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