Need help with gas leak in my 73S.

[merbesfield]

I have a strange gas leak and need some help. Sort of long, sorry. I filled up the tank. Upon filling I noticed fuel poring out of the plastic tank under the front drivers side fender. The gas appeared to be running from the top of the tank down to the bottom and spilling onto the horn. I have also noticed strong fumes in the car and it is going through gas very fast, ie. goes from full to half tank fast. You can also hear a very noticeable gurgling sound coming from the gas tank after you have drive the car for any good distance and park it on level ground. Sounds like bubbles or gas being pushed back into the tank. Remove the gas cap and it is clearly inside the tank. The two lines that run from the back of the car to the charcoal canister in the trunk are no longer connected if that has anything to do with this. I dropped the car off at Franz's shop today and he said he has never heard of this problem before, not very reassuring. Any help would be appreciated. Thanks, Mark

[72targa]

I don't know...but I would be pulling things apart and getting it fixed before anything BURNS!

[Grady Clay]

Mark,

I agree with Peter; fix before fire.


There is likelihood that the expansion tank in the LF fender has a crack.
Take the tank out, clean and inspect it.

Are all your vapor hoses original?
If so, you have your work cut out for you but it is absolutely necessary for your safety and enjoyment.




You are not alone with this issue.
Porsche’s choice of material for some of these parts wasn’t adequate for the task.
Some had issues within a year or few of new.
I suspect you will find the vapor tank broken at the small vent barb at the top.

There is also the result of a ‘bean counter’ vs. engineering compromise.
Since the vapor hoses are not pressurized, they did not originally have clamps, the barb was deemed sufficient.
As it turns out, the hoses shrank and pulled off the barbs.



What to do?
Search and study first.
Post a plan (here & Pelican) for peer review.
Buy parts.
Fix.
Post (here & Pelican) your results and links for the next owner.


This thread has all three of the diagrams for your 911.
http://forums.pelicanparts.com/porsc...le-shroud.html

Here is info about the clamps:
http://forums.pelicanparts.com/porsc...ml#post5791453

Another place:
http://forums.pelicanparts.com/porsc...-73-coupe.html

Many of these threads have more info:
http://forums.pelicanparts.com/searc...archid=6535511


There may be more to your loosing ‘top-off’ fuel so fast but this is a good start and necessary 38-year maintenance.

Best,
Grady

[edmayo]

Mark, if you care to, McMaster-Carr has the yellow color vent hose rated for gas usage. Here is a picture of it installed in a 66 I restored for a customer.

[merbesfield]

The car is definitely getting fixed before I drive it.

Ok, some questions after review of flow diagram. Not sure what item no. 1 is, but must be some emission part? According to the flow chart, if the tank is overly full, the overflow fuel should enter the plastic tank from the bottom and vapors go out the top. So that leads to a big question, why is fuel flowing from the top of the tank? Is that tank so full of fuel it is leaking out the top, very scary. The system seems pretty basic to me, though I have no idea what the engineers had in mind. However, it is possible that with the two lines in back disconnected, the system is not flowing properly and/or if there was a blockage it could lead to a reverse flow of sorts, which would explain the gurgling of gas flowing back into the tank that I hear after driving it. I think I will go to the shop tomorrow and work with them on this. Two/three minds might be better than one. Your input is appreciated.
About the clear/yellow fuel lines? Were they originally clear or yellow to start with? The hose Ed shows in his pic does not look correct in color to me, too yellow? McMaster sells some metric fuel hose that is listed as clear. I never saw one of these cars when it was brand new back in the day. Clear or always yellowed? The two hoses running from engine compartment to the front are the fabric covered variety and are definitely no longer connected to the system.

Who sells the original style fabric covered lines that run front to rear? What are the sizes?

Who sells the clear tubing that is in front? What are the sizes?

Clear metric fuel line at McMaster

Thanks for all the help.

PS, shop checked my injectors today and did a leak down test. Leak down numbers were excellent. No issues. One injector was not spraying properly so we ordered one. Hope that fixes the low 2200-2500 RPM bucking and popping issue.

PSS, are the expansion tanks still available new?

[edmayo]

Mark, the fuel vapors come from the tank, go to the vapor collector up under the cowl, then join the hose from the filler neck which then goes to the welded fitting in the inner fender panel then through a rubber hose to the bottom of the vapor cannister in the fender. the vapors then go through the small hose to the charcoal cannister. A hose leads from the back of the fan housing of the engine to the charcoal cannister delivering pressurized air from the cooling fan to the charcoal cannister. This pressurized air then goes through the charcoal cannister to the second hose to the inlet on the back of the air cleaner where it is drawn into the engine, thus preventing fuel vapors from going to the atmosphere.

The fabric hoses to the engine are not fabric all the way, they are attached to steel tubes through the tunnel. This fabric hose is available from Wurth.

I agree the hose I've shown is not exactly the same amber tint as the original, but it is the closest I've found to date, and it is fuel vapor rated.

As Grady stated, you should remove the vapor cannister from the fender, I'm sure you'll find it cracked someplace. Might be fixable with plastic welding, (like a soldering iron tip to melt things back together)

Don't know why you get the gurgling in the tank, but I'd start with an inspection of all the plastic vent lines in the trunk. You do want to ensure the tank is actually vented.

[merbesfield]

I am going to bet that something is routed/installed incorrectly. The tank along with all the lines were recently replaced after the car had sat for so many years. Maybe something got installed in the wrong order plus the fact that the lines from the rear a not connected could be a problem. Can anyone comment on whether the vapor lines were clear or amber colored from the start in 1973?

As for the fuel flowing out of the top of the under fender tank, that is not a good sign. As you say, I am sure the tank is either cracked or the hose has been pulled from the tank. That does not explain why there would be fuel flowing from the top of the tank. Shouldn't there only be vapors flowing out of the top of the tank? According to the arrows on this picture, excess/overflow fuel would enter the tank from the bottom and any vapors would flow out of the top. So again, why was fuel flowing out of the top of the tank? I will remove the tank and investigate. See pic with added notes.

[Grady Clay]

“The two hoses running from engine compartment to the front are the fabric covered variety and are definitely no longer connected to the system.”

Check that the two disconnected vent hoses in the engine compartment aren’t plugged.
If so, remove the plugs.
If those have been plugged, the fuel tank becomes a ‘sealed system’ when the gas cap is on.
The fuel/vapor will find some way to escape when it expands (refueling with cold fuel in hot weather).
This can push hoses off barbs and break plastic containers.

“Is that tank so full of fuel it is leaking out the top, very scary.”
Even a little (<<1 psi) can crack this already insufficient tank.
The tank is probably NLA but worth asking.
A lot of these components are the same as VW, Audi and other period German cars.


The vent hoses were originally clear but quickly gained a yellow-amber tinge.
There are Wurth & more fabric covered hose (like in the engine compartment) of the same size.
Not original but what Porsche should have used in the first place (with clamps).


The ‘gurgling’ you hear occasionally is fuel boiling in the MFI pump and engine compartment components and being forced back to the tank, bubbling up from the bottom fittings.

Best,
Grady

[edmayo]

Just another thought here Mark, was the tank ever boiled out and then slosh sealed. If so the possibility exists that the sealant clogged the vent tube from the top of the tank. Remove that vent hose and pressurize the tank a LITTLE with an air gun, you should be feeling an air flow out that vent tube.

[merbesfield]

Does anyone know the sizes of the clear tubing up front? I want to order some samples of some clear vapor line to see how it compares. Thanks