Help identify a line on my airbox

[vick]

Car is an ‘81SC row. On the drivers side of the airbox there’s a hard plastic line loosely fitted, about 6” long and crimped at the end. I don’t see it in the PET and don’t see anywhere obvious it would have run.

Anyone know what it is/was? Can I remove it and plug the hole in the airbox? The hole is behind the air filter and I assume pulls pretty good suction, so a plug would have to be pretty secure to avoid ingestion.

Any ideas welcome, thanks

[HarryD]

I suspect it is part of your vapor recovery system.

This post by the late Grady Clay (who had encyclopedic knowledge of the 911) may be helpful. I think it is line 6 in the last drawing.

https://forums.pelicanparts.com/porsche-911-technical-forum/1133548-fuel-expansion-hose-venting.html

Originally Posted by Grady Clay

tref,

In the third diagram I posted above (labeled “05” is an
exploded parts diagram) the hoses from the rear of the
tunnel to the fan shroud and air filter assembly are
#22 and #23. In the trunk and to the front of the
tunnel (by the steering rack) are hoses #20 and #21.
Not labeled with a number are two plastic pipes in the
tunnel. Hoses #20 & #23 are 5 and hoses #21
& #22 are 6, including the un-labeled plastic pipes
in the tunnel.


Philippe, here are the later versions, starting in ’74.

Is the plastic vent pipe original in your RS?


1974 to 1977.
"
"
© Dr. Ing. h.c. F. Porsche A.G.


1 – Fuel tank
2 – Expansion chamber
3 – Activated charcoal filter
4 – Cooling fan upper shroud with hose connector
5 – Hose from cooling fan to activated charcoal filter
6 – Hose from activated charcoal filter to engine air filter
7 – Engine air filter
8 – Return hose connecting fuel tank with expansion chamber



1978 and later.
"
"
© Dr. Ing. h.c. F. Porsche A.G.


Some features to note:

The Expansion chamber hose to the fuel tank is at the
bottom of the chamber. This returns any liquid fuel to
the fuel tank during cool-off. Ideally this hose should
be continously down hill to the fuel tank. The vapor
only hose to the Activated charcoal filter is at the top
of the Expansion chamber with baffles.

While the ’78-> system is slightly simpler, the ’74-’77
system won’t give sudden surges of vapor to the
engine intake.

The ’69-’73 system had plastic hoses in the trunk. Over
time, temperature and fuel vapor, they shrink. I think
they all should be replaced with the braided fabric over
rubber hoses. These were not originally equipped with
hose clamps. Every connection should have the Norma-
Schellen (NS) clamps. Fuel vapors in the trunk can lead
to disaster. The little expansion tank under the cowel (1
in the early diagrams) can split a seal from age. That
should be inspected also.

Even race cars should have a proper vent system that
includes an expansion tank.


Best,
Grady

[vick]

Originally Posted by HarryD

I suspect it is part of your vapor recovery system.

This post by the late Grady Clay (who had encyclopedic knowledge of the 911) may be helpful. I think it is line 6 in the last drawing.

https://forums.pelicanparts.com/porsche-911-technical-forum/1133548-fuel-expansion-hose-venting.html

Thanks Harry, that looks right. Interesting though as there’s no sign of the other line that diagram shows starting at the fan shroud, or a canister I can find anywhere. There is similar material line that’s routed up the left wheel well that just ends open - that seems to route back from the expansion tank in the front left fender.

I’ll cut this out and find a good plug for that hole, really appreciate you pointing out those diagrams

[HarryD]

Originally Posted by vick

Thanks Harry, that looks right. Interesting though as there’s no sign of the other line that diagram shows starting at the fan shroud, or a canister I can find anywhere. There is similar material line that’s routed up the left wheel well that just ends open - that seems to route back from the expansion tank in the front left fender.

I’ll cut this out and find a good plug for that hole, really appreciate you pointing out those diagrams

Per the last drawing (which should be your car), there is no line from the fan shroud to the charcoal canister. Do you smell gasoline fumes after you fill or while driving. If so you need to do something to control the fumes.

If you duplicate the 1969 system in this post by Grady it may get you there.

Originally Posted by Grady Clay

Here is the 1969 Evaporative Emissions System


© 1969 Dr. Ing. h.c. F. Porsche K.G.
This shows the fuel system for the 911T (pump at rear), #2, 4, 16, 17.
and
the fuel system for MFI 911E & 911S, #3, 4, 7-10, 16-19, 37-42 and more.
(In 1970, the 911T is plumbed as the 911E&S here.)





The ‘tee’ fitting (#44 above) does not show a 3rd connection here.
My recollection is that is the small vent hose to the filler neck.

The outlet goes through a grommet (#47) in the front panel behind the windshield washer reservoir.
It vents between the front bumper and the inner panel.





System for '70-'71.

© 1970 Dr. Ing. h.c. F. Porsche K.G.


Best,
Grady

[vick]

Originally Posted by HarryD

Per the last drawing (which should be your car), there is no line from the fan shroud to the charcoal canister. Do you smell gasoline fumes after you fill or while driving. If so you need to do something to control the fumes.

If you duplicate the 1969 system in this post by Grady it may get you there.

My mistake, I was looking at the pre-78 diagram. This looks like what mine was before the line was severed. No fumes and no concerns, I think the line terminates far enough back that any vapors dissipate. I removed the line from the air box and will find a suitable plug.

Thanks again for helping me narrow it down!

[pmax]

That looks homegrown.

[911mhutch]

Sure does look home grown

[PeteKz]

From your description it looks like someone removed much of the vapor control system. If so, and you don’t smell gas fumes now, you should consider leaving it as is.