WUR Return Fuel line

[Brian Fuller]

The prior owner replaced the fuel line from the WUR to the main fuel return line rail with a low pressure fuel line. I am assuming that this fuel line is not under the same pressure as the rest of the injection system? There is no evidence the replacement line has ever leaked.

Do you think it would be ok to simply replace the exsiting line with the best 60 – 70psi fuel line I can find at my local auto shops? I looked for hours for specs regarding the pressure from the WUR to the fuel return line but could not find anything.

All the Best,
Brian


1978 Porsche 911 SC (barrowed these pics since I already pulled the lines)

[T77911S]

the return line from the WUR should go back to the fuel distributor (FD).
the FD has a check valve in the system pressure reg that closes when the fuel pressure drops a certain amount after the pump shuts off.
this helps with residual pressure. it helps to start with a higher pressure AND to maintain that pressure.
with out the check valve pressure could leak past the WUR and back to the tank.

if your WUR return line is connected directly to the return line back to the tank, you would not have any pressure on that line.
for it to be connected as you say there would have to be a plug on the back of the FD where that line should be connected.

have not looked at one of these in quite a while.

[Brian Fuller]

OK, I think I figured it out. Thank you for your reply. I must have re-read your post six times. Something was just not right. My return from the WUR was not going back to the FD. Then, I got it! I have a Frankenstein. The prior owner did some "creative" thinking. I looked at the PET more carefully and see that the PO welded a additional bracket on to the return line and instead of running the return from the WUR back to the FD, he ran it back to the return line. See illustration below:

It does not appear that these fuel lines are available anymore. Hence, why the previous owner probably did what he did. I am still under the persuasion that these lines are not under a lot of pressure and that I may be able to build a set. (Unless someone out there has a nice clean set)

Looks like what I need will look something like this (see below) with a line from the WUR returning to the FD:

[Brian Fuller]

This just got a little more interesting. A friend sent me the pic below. The return lines up thru 1977 look almost exactly like like the one on my 78'. (Except someone did do some changes to the original on my car). Is it possible that Porsche put a 77' return line on my 78' car?????

[kenikh]

^ especially if it is an early 78 car, it is possible

[Rawknees'Turbo]

Originally Posted by Brian Fuller

It does not appear that these fuel lines are available anymore. Hence, why the previous owner probably did what he did. I am still under the persuasion that these lines are not under a lot of pressure and that I may be able to build a set. (Unless someone out there has a nice clean set)

If you wanted to, you could take the current hose assembly to a hydraulic shop, and they would re-build it with high pressure, ethanol friendly hose (re-using the existing fittings and replacing the old hose and crimps with new). There is a "Mom & Pop" shop in the Dallas area that I have used for many years (everything from oil to refrigerant hose) - the finished pieces look better than new and at very reasonable costs, too.

[Brian Fuller]

Rawknees, Thanks for the tip. I think I'm getting closer to figuring out this puzzle. I just got home from work, looked at my CIS and looked it up. It is not from a 78' but appears to be from a Euro 77'. Now I know why the fuel lines are from a 77'!!

[BoxsterGT]

I would expect that your original was a Polyamide line which was commonplace then.

I have had pretty good luck re-making these lines if the original metal fittings are still good..........





For inquiries, please.....email me only.

Len at Autosportengineering dot com

[Brian Fuller]

Len,
Thanks. My only problem is I don't have a good original return hardware. Mine is a Frankenstein with an additional nut welded (brazed) on to the end of the original nut

I'll probably need to purchase a new one that has a single piece of hardware with both the return barb for the WUR and a barb to the accumulator. Like the one in the pic below:

[T77911S]

the early cars, (pre78 I think) had a different system pressure reg on it.
your pressure reg has a check valve in it that closes when the fuel pump is turned off blocking the return of fuel from the WUR to help with residual pressure. at this point you DO have pressure on the return line, probably around 2-2.5bar.
while it is running there is really no pressure on the return side unless there is a restriction going back to the tank.

I had a 77 but cant remember where the return line went, but I am thinking it is how yours is now connected.
there are lines out there that people have removed with their CIS.


good job brazing that on.

[BoxsterGT]

That actually is quite creative. Why don't you keep what you have as long as it is not leaking. The Polyamide tube is much more durable, but if what you have works, then...........Drive it and enjoy.

This is on the low-pressure side of the system so not a big deal. If you are still concerned, pull the hose and show us the barbs on the PO custom fitting. They are different. between hose & poly. If anyone wants to see the differences I will post photos.

If its a hose type you must keep hose. If its a Polyamide type fitting then you must go to a Polyamide tube

Len

[Brian Fuller]

Len,
You're right, it probably would have been fine. (The PO was driving it around and had not problem). However, I decided to pick up a new line. I just did not like the "welded" on piece.