tank ventilation-MFI diagrams

[philippeF]

Hello
May you post, or send by mail, the part diagrams for :
the tank ventilation system
the MFI complete system (filters, lines, pump ......)

2.7 Rs MFI engine.
Thanks
Philippe

[Grady Clay]

Philippe,

Here is the evaporative emissions system (fuel tank vent) for 1969 to 1973.
FuelEvapEmmissions69on03.jpg
"
"
© Dr. Ing. h.c. F. Porsche A.G.

1. Expansion Chamber
2. Vent Chamber
3. Activated charcoal container
4. Engine fan upper shrouding
5. Pressure line from fan to activated charcoal container
6. Purging line from activated charcoal container to engine air cleaner.


02a
"
"
© Dr. Ing. h.c. F. Porsche A.G.

04
"
"
© Dr. Ing. h.c. F. Porsche A.G.

05
"
"
© Dr. Ing. h.c. F. Porsche A.G.

06
"
"
© Dr. Ing. h.c. F. Porsche A.G.

Best,
Grady

[randywebb]

Wow, Grady -- 1969 to 1973, no matter what fuel delivery system? Does it include 1973.5 CIS?

Note:
#1 is up under the cowl - access from the trunk.

#2 is up under the LF fender and is surely a cracked up remnant by now. Also NLA IIRC. I plan to use a water bottle there.

#3, carbon canister is NLA. You can get a VW one for about $70. It is a big oblong thing that is at the LF by the spare tire on a '73 and by '75 had moved to the RR above the wheel hump.

Who has pics to post to help others?

[Grady Clay]

Randy,

I looked in the workshop manuals and tech infos and can’t confirm either way about a ’73.5 911T CIS. I suspect it is the same as MFI and carbs ’69-’73. If I have time I’ll look in the parts manuals and PET. The system changed in ’74 (simpler). I posted on a prior thread about the later systems.

Pelican Brant is picking me up tomorrow and we are going to the vintage race (his 914-6) in Hastings, NE. I’m a little short on my chores.

Hopefully this is what Philippe needed, it is 2 AM there.

Best,
Grady

[HarryD]

Randy,



This drawing looks a lot like my 73.5 CIS setup. If you need pictures, I shoot some for you. For the tank in the fender well, call Gary at Parts Obsolete. He sold me one from a later year for $5.00 and after some Hillbilly Enguneering, it was installed. See the story here: Vapor Tank Replacement

Does anyone have the sizes of line#'s 24, 25, 27, 28, 29, & 30?

[philippeF]

thanks grady !

unfortunately, as my car has been modified, it seems this is not the same configuration... more simple...

[tref]

I'm trying to locate where the hose #5 and 6 are physically supposed
to be. The whole system is missing from my car and I'm sure the hose
(or part of them) are still in the car but where are they routed in the
engine bay and the trunk.

Thanks,
F.

[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

[randywebb]

"replaced with the braided fabric over
rubber hoses."

- There is a special 'clear' hose made just for fuel vapor that you can use - it is in an old post by Jim Sims. Any big hose shop will have something. Do NOT use regular PVC.


Grady - do you think people with older cars should 'upgrade' to the 1974-77 layout?

[Grady Clay]

Randy,

"Grady - do you think people with older cars should 'upgrade' to the 1974-77 layout?"

No. I think just good maintenance is the order of the day.

If I had to install a evaporative emissions system in a car, my first choice would be the ’74-’77 if it complied. I think the reason they changed in ’78 is when the 911 is parked the vapors bypass the activated charcoal and vent into the fan shroud (there isn’t a check valve).

The next time I’m by one of the dealers, I’ll look into the current system that holds pressure on the fuel tank.

Best,
Grady

[randywebb]

I think current systems use 2 or more pumps.

But it would still beinteresting to see the layout.

Thx, as ever, for your posts.

[HarryD]

Originally posted by Grady Clay

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.

Grady,

My trunk has the aged plastic hoses (with clamps). I hear you on the rubber hose but I need to get a handle on the required ID's Do you have that info?

Thanks.

Harry

[philippeF]

Hello

I've almost ended my car restauration project, but i have to complete the tank ventilation....

is there any more simple solution you've tried ? (i mean a diy solution), (i don't have the parts listed on the pics here)

[Peterfrans]

Sure,

You could go for the simple setup as used in non US cars. Only one hose to the expansion cannister under the dash and another hose that goes through a grommet behind the front bumper. I did this as several hoses and cannisters were leaking. No more fuel fumes for me now.

[philippeF]

thanks Peter, i'll try this.

[Peterfrans]

To add, the y-connection marked 55 in the drawing connects to the overflow hose from the brake fluid container.

[HarryD]

Originally Posted by Peterfrans

To add, the y-connection marked 55 in the drawing connects to the overflow hose from the brake fluid container.

Peter,

Why on earth would anyone ever allow gasoline fumes to mix with brake fluid? 55/56/57 is connected to the vent at the filler neck.

[pope]

philippeF, I think we may be in a similar situation. Mine is described here:
Missing fuel bleeder (breather) container?

I was looking at the diagram that Peterfrans put up and thought that both hoses from the cannister went to the tank.

Peterfrans,
you say the second hose goes through a grommet in the fender. Do you maybe have a picture of this? Also, where exactly is the cannister hooked up?

A word on hose sizes and maybe somebody can add something. The connection on top of my tank is 16mm. Between that and the top of the filler neck there is an intermediate piece which is not a T-junction but a barb adapter from 10mm to 9mm. The hose from the tank to the piece (grey in the picture) is somewhere between 12-14mm and someone managed to craftily put it over the 16mm connection on the tank (I have no idea how). The other hose (black) is a normal 9/15 ID/OD hose.

Both of these hoses are very old in my car. I had a difficult time removing the small one so I had to cut it of with a razor. I did not attempt to remove the big one because that one is thoroughly stuck to the tank connection and I do not have a replacement for it at this moment. I went about shortening that one on the piece side and replaced the 9mm hose with a longer one.

[HarryD]

I found this thread again and after reading it over, I have a question.

Currently, I have a 1973 Fume recovery system that looks like this:



Is there any reason I cannot replumb it to match the later design that looks like this?



In particular, I am thinking of eliminating the tank behind the dash (#1) and reroute the hoses to go directly to Tank #2.

[wicks]

On the '73 system here, is there a quick way to tell which of the two large pipes in the engine bay are which?

One sucks from fan shroud and other blows evap into air box.

They are both the same length and had them unplugged for a month, didn't mark em. Oops!