WUR return line
 

My cold start problems remain, I have cold control pressure of 5 bar. I removed the wur, and am hesitant to open it up if I don't have to. Is there a way to check the fuel return line, say by blowing air thru? I have an '83 the # on the wur is 072, and it has a vacuum line.

You should be able to blow air back through the return line into the gas tank. Take the gas cap off before you do this. But it's almost certain that the WUR is plugged if your CP is the same as your SP. Look in the top of the CP fitting and see if there's any crud in the screen.

Screen looks good. I have tried to blow using lung power, no joy. Perhaps I should try 10lbs of compressed air?

5 psig of compressed air should be sufficient to hear bubbles in the gas tank. Don't do that for more than ~10 seconds - you'll be generating lots of flammable gas vapor. Do this outside if possible and no flames!

Testing with the pressure-end of a MityVac air pump (or similar) is safest; even a tire pump is useful.

Take the return line off the WUR - don't try to blow through the WUR.

WUR Return Line………
 

Boom,

Your WUR-072 has no vacuum line. It is not a vacuum assisted WUR. Double check the connection of the small rubber hose on top of your WUR to the throttle body. It should be connected to a vent port.

There is flow restriction in your return line. The restriction could be caused by a clogged WUR or blockage any where along the fuel return line. Use your CIS pressure gauge to locate the culprit.

If you are not familiar with the test procedure, I could do the testing for you for FREE. Send your WUR to me with a RSL (return shipping label) preferably a UPS. The test takes only several seconds and you could watch and measure the return flow using an appropriate set up.

If the WUR passed the test, you need to break down your return fuel line starting between WUR and FD, FD to main return line, etc.

Tony

Thanks for the replies. And thank you to boyt911sc for the offer. I have already fitted a small hose to the return line and will try to clear it with low pressure. Wish me luck, the weather is too nice not to be driving.

CIS Troubleshooting…………..
 

Boom,

Do you have a CIS pressure gauge kit? Use it to pressure test your system with a running FP. You know it is clogged and you have to determine the location to be able to correct the problem.

Tony

Let's be clear about this: blow air through the return line only, NOT through the WUR and return line. You should be able to do it with lung pressure.

When was the last time you replaced the rubber fuel lines and rubber return lines, including the one that goes from the forward tunnel to the tank?

It's time, I guess. I was trying to avoid an engine drop, but it's almost time for winter hibernation. I did want to get a few more driving weeks in, but really don't like the hard start issue.

Unnecessary Engine Drop……….
 

boom,

It is unnecessary to drop the motor to test your fuel line return line. You could do all testing with the motor installed.

Tony

I tested the line by disconnecting by the WUR and blowing after removing the gas cap, first by lung power and later with a bike pump. I hope that this was the correct procedure, as once I found that the line was totally blocked I attempted to remove the other fitting on the fuel distributor. This did not go well, the fitting was apparently stuck to the tube and -no surprise after 41 years. Gave up trying that, tightened it, and now it leaks. If it's possible to replace it with the engine in situ, I would be very happy, What say you?

:)

I am having trouble understanding what "return line" the above conversation is referring to.

For an 83 SC USA model, your CIS Main Return line should look like this.....

http://forums.pelicanparts.com/uploa...1726531952.jpg

...and the line between the FD and the WUR should look like this.....

http://forums.pelicanparts.com/uploa...1726533228.jpg

I am not clear on which "return line" you are referring to.

With Polyamide tube, if you have a leak at any of the connections the line must be Removed and Replaced or Re-Made.

Yes you can do this in place, but it's advisable to use crowfoot wrenches and use the utmost care to prevent damage to the fittings or connection.

I will look up the Porsche bulletin on these Polyamide lines and post it for all to see.

Len Cummings

:)

:)

For all CIS systems from Model Year 73.5 on until the end of the SC model for 1983.....

http://forums.pelicanparts.com/uploa...1726534299.jpg

Hope this helps.

Len

:)

:)

One more of the CIS Main Return Line......

http://forums.pelicanparts.com/uploa...1726535914.jpg

.... from another 83 911SC.

Len

:)

Len, thanks for the response, the line is definitely the return line, as shown in your first pics, the one with the red tape. From what I have seen on various posts about this, the end that attaches to the distributor is located on the back right side. I was attempting to remove it to see if I could clear the tube and apparently twisted the tube, which had welded itself to the fitting after 41 years. Is this line the same for all Lambda cis?

:)

This is unique to the 80-83 911SC models.

Here is one I Re-Made with new Polyamide tube a while back before I was able to find a suitable rubber cover.....

http://forums.pelicanparts.com/uploa...1726613235.JPG

Often I receive them crusty and bent out of shape.

The red Fixture shown above was made up so I could straighten them back to semi-original shape.

I then send them out for yellow zinc plating, and when back I fix new Polyamide tube and rubber covers.

Here are a late SC Main Feed and Main Return as yours should be.....

http://forums.pelicanparts.com/uploa...1726614188.jpg

I don't know if your damaged one can be repaired or not, but I am willing to try if you send it to me.

The only alternative I can think of is a replacement.

Len

:)

Len, I don't think I have explained myself well. The line I am talking about is a single line, going from the wur to the back of the fuel distributor. I have traced it by following it with my hand. It is only one line, with regular fittings (non-banjo) on both ends, that fit a 10mm wrench.

:)

Guess a photo is needed. There are two FD to WUR Lines, one with 8mm Banjos and one with M12 Threads.

I did not know there was a Feed and a Return here, thought they had to do with differences in Fuel Pressures.

Are we talking about this one ???

http://forums.pelicanparts.com/uploa...1726687754.jpg

If not, then show us a photo.

If it is, and the steel line is twisted and deformed at the FD, then a replacement is necessary.

I do not think this is available from Porsche any longer, so used may be the only choice.

I will look for one in my collection.

Len

:)

Thanks much, Len. That's the one I need. It would be great if you have one.

Gary ;-)

The line that I am talking about is solid tube end to end, with a 90 degree bend where it comes out of the wur and another at the end at the fd. I will take a pic and post.

On a side note, the 072 WUR is for an 80.

Was it replaced at some point for your 83 ? What does the Lambda control unit look like, under the seat ?

:)

Gary-

I could not find a solid one piece steel line, but the earlier CIS models all use Polyamide tube and I make these up all the time.......

http://forums.pelicanparts.com/uploa...1726749053.jpg

http://forums.pelicanparts.com/uploa...1726749088.jpg

I am happy to help, but it's best if we converse directly by email.

len.cummings @ verizon.net but without the spaces.

Len

:)

Pmax, it is for sure an 072, I was surprised as well. I will take a look under the seat, what should the unit look like.

Gary

Pmax, it is for sure an 072, I was surprised as well. I will take a look under the seat, what should the unit look like.

Gary

To be clear, the 072 should work as well but it's good to establish the baseline, so to speak.

What happened to the return line ?
Where is the leak ? The metal portion is often subject to abuse ... the one in Len's post is above is typical after years of handling ... but seems to hold up.

Mine line looks great, problem is I have been chasing a cold start issue ever since I got the car 5 years ago. I did all the checks, vacuum leaks, fuel pressures and electrical connectors. Took it to a highly respected shop and they replaced the cold start valve. The car ran worse than before. I should have sent it back, buy I am a stubborn old man and wanted to prove something or other. Anyway, I have been getting a cold control pressure of almost 5 bar, which seems to point to a blocked return line. So. I tried to blow through it first by lung and them with bike pump. Line would not allow air to enter. I then attempted to remove the line at the fuel distributor end, only got it to turn ¼ turn before encountering stopping, as I was not getting any easier to turn. Most likely the line has fused to the nut and as a result was damaged and is now leaking.

Learn And Listen………
 

Boom,

Talking about old and grumpy men, you are not going to fix this CIS problem unless you listen to people with experience. We are talking a couple of minutes test to identify and locate the culprit and you failed to do it. Or refused to accept the suggestions. And this problem is not going away. Good luck.

Tony

@boy911sc, not really sure what you mean. I conducted the tests to determine the issue, as described, what else do you suggest I do? I have a cold control pressure of 5 bar, what else can cause that? I really appreciate all the great advice.

Take your time, don't need to force anything, you're only 2 pages in ;) Replace that busted line with Len's or post a WTB. I'm impressed you could get at the fittings in front of the FD given the limited room there.

The fuel return from your WUR goes thru the fuel distributor as detailed in this post below given it's a later CIS.
https://forums.pelicanparts.com/porsche-911-technical-forum/1159640-fuel-pressure-testing-system-pressure-cold-control-pressure-residual-press-0-a-10.html#post12271194

Fyi………..
 

Gary,

Very few people know this secret. WUR-072 = WUR-090. They are the same and identical except for the stamped # on them. If you don’t believe me, investigate and inspect every single component and compare. I don’t want to take this secret to the grave.

Tony

Great to know, Tony. Would you take a look at my wur, please.

FREE Testing And Evaluation…..
 

Gary,

Yes. Send your WUR to me less fuel line fittings and include a RSL (return shipping label) preferably a UPS. Schedule it to arrive after my Engine Rebuilding Workshop. I have suspended my CIS activities during the WORKSHOP. Will PM you the address.

Tony

072 and 090 charts are here.

https://forums.pelicanparts.com/porsche-911-technical-forum/758788-cis-troubleshooting-dummies-4.html#post9671930

Squinting a bit, they do look the samel.

There is a negligible difference between the two (2) charts by 0.05 bar (0.73 psi.). If you plot every data point points for -072 and -090 control pressure charts on the same chart, the difference is negligible. The pressure gauge tools we use is not capable of detecting the pressure difference unless you have precision laboratory equipment to use.

Tony

Harbor Freight CIS Gauge Kit…….
 

Gary,

Do you have a HF pressure gauge kit tester? I hope not. Keep us posted. Thanks.

Tony

A Quick Look………
 

Gary,

Before you send your WUR, could you post a close-up shot of the WUR? I am interested to see the top particularly the area where the plug is located. Thanks.

Tony