Unfortunately, I didn't know what "RP" meant back then.

Now I know!

Andy

We could almost discuss CIS using only abbreviations.

lol. Yes we probably could!

So I tested the WUR to FD fuel line, and the WUR return line.

I disconnected both ends of the WUR to FD line and easily blew air through it. But the WUR return fuel line is much more difficult to blow air through.

However, I just now read that the WUR return line goes to the FD, not directly to the fuel tank. When I tested it, I had only disconnected it from the WUR, not the FD.

Should I disconnect it from the both the WUR and the FD to test that it's clear?

Disconnecting it from the FD appears to be non-trivial!

Andy

Look at the routing from the WUR return line. It should go directly to the hard line at the front of the engine on the left side. Show a picture of the routing of your return line. There will be some resistance to blowing through the return line to the tank because you have to blow through a long fairly thin hose with fuel in it. Can you (or an assistant) hear bubbles coming through to the tank if you put your ear next to the filler?

Thanks Pete, I may be mixing up the names of the two lines.

My car is at my office, I'll be there tomorrow in the AM and can take a photo then, and have someone listen for bubbles in the tank.

But that line that we're talking about, that I only disconnected one end of (the WUR end) and that is hard to blow air through, and I thought was called the WUR return line, is a thin hard line that starts at the front side of the WUR on the passenger side of the engine and then goes forward toward the firewall, makes a 90* right turn, and then goes between the firewall and the front of the engine toward the passenger side of the car.

I can't see where it goes after the 90* right turn, but I think it goes to the front side of my FD?

I think the front side of my '81 911SC FD has three lines coming into it, with one being the WUR fuel return line? Like the image at this link shows?

https://www.google.com/imgres?q=1981%20911sc%20fuel%20lines&imgurl=https% 3A%2F%2Fwww.eurospares.co.uk%2Fimg%2FixMAAMTaOU7v7 qMsi2X59H1JEZQhGoUG6W7P5orvF4UZzU44lFWoTGOHAQM%253 D%2Fporsche-911-(1981)-part-diagram-107-010.webp&imgrefurl=https%3A%2F%2Fwww.eurospares.co .uk%2FPorsche%2F911%2F911_(1981)%2FPartDiagrams&do cid=SYPyKPzy-7e97M&tbnid=41DiU9g5a7izgM&vet=12ahUKEwiO_I2qk_aJA xXRHUQIHQ9rAFs4FBAzegQIMRAA..i&w=1100&h=800&hcb=2& ved=2ahUKEwiO_I2qk_aJAxXRHUQIHQ9rAFs4FBAzegQIMRAA


The photo below is not my own engine, but you can see the same thin hard line leaving the front top of the WUR and going toward the firewall in front of the engine:

http://forums.pelicanparts.com/uploa...1732491146.jpg

I hope this makes sense.



Andy

Andy, I forgot that your car has the OXS system. I looked at the image you sent, and it appears to be different than mine. However, the Bentley manual shows the same routing of the WUR return line for SC's generally, so I don't know. At any rate, it is a return line, so it flows back to the tank.

Fuel Return Line……
 

The fuel return line from the SC WUR goes back straight to the FD through a PUSH VALVE. That’s the reason you could NOT easily blow air through it unless you use compressed air. After the push valve, the return fuel goes to the main return line connected to the gas tank.

Tony

Thanks Pete. It appears that the line connected to the back of my FD that's closest to the camera is my WUR return. At the very least I can disconnect it and check for flow to the WUR.

http://forums.pelicanparts.com/uploa...1732556336.jpg

Andy

So I disconnected the WUR return line from both the FD and the WUR, and blew through it. It is not plugged.

I then connected the line back to the FD, and it was extremely hard to blow through.

Then I checked my NEW multimeter's accuracy by measuring resistance on several resistors. It read 22.1 on the 22 ohm resistor and 33.0 on the 33 ohm resistor.

Then I pulled the elec connector off my [edit: 090] WUR and tested resistance on the two male prongs and got 26 ohms @ 64F. Measured multiple times and got the same result.

I guess this means the WUR is out of spec?

Then I tested pressures:

@64F
SP: 4.6 bar
CCP: 0.7 bar
WCP: 3.4 bar, @ 2 minutes
RP: 0 bar, @ 1:10 minutes

The RP dropped and then held at a little over 1 bar for 20 seconds or so, but then dropped like a stone to 0.

I guess I'll now do the other tests Pete suggested.

Andy

Well, the FA test was interesting.

As soon as I removed the bottom connection, fuel poured out of the FA. Like at least a cup of fuel, maybe more. In the chaos as I was grabbing shop towels I forgot all about Pete's "plug the line" instructions although I didn't notice if any fuel came out of the line.

After the fuel stopped pouring out of the FA, I cleaned up the mess and dried everything off as well as I could, and then turned on the FP.

Yes, fuel poured out the bottom of my FA like it was a kitchen faucet.

Finally, I have a smoking gun for my intermittent no-start issue. Broken/ruptured FA diaphragm. Right?

Andy

Yes. You know that you need a new FA, so replace it now. It may or may not be the only thing that's causing intermittent no-starts, but it is surely contributing.

Thanks Pete, I just ordered a new FA and fuel filter from our host.

I'm not sure I'll get the parts and be able to install them before Thanksgiving, but I may. I'll post when I do.

I thank you so much for sticking with me during this long saga, and wish you and yours an amazing Thanksgiving!

Best,

Andy

Andy, thanks and hope you have Gemutlichkeit with friends and family too.

Check the mixture and CO value after installation of the new FA. It's influence in the mixture is massive! Especially when it was bad because mechanics ruled it out by enriching or leaning the mixture...

I don't know how I didn't see this before, but I didn't.

Thanks Tony, that answers a lot!

Andy

Just a quick update. I replaced the FA and FF before Thanksgiving last week and, so far anyway, the car has started easily every time. So maybe 20 starts with no problem, while before I was getting no-starts every 5 or 6 tries.

I've only been able to drive it sporadically since before Thanksgiving and I'm out of town until Friday of this week, so while I haven't been able to test the starts extensively yet, I'm feeling hopeful!

Thanks Thomas. I did have a backfire today so it does sound like the mixture and CO need attention as well.

Andy

Well, I was out of town for 4 days last week and now, for the past three days, the car has started every time. So I will say the intermittent no-start issue has been resolved!

Thank you to all for all of your help!!! Very, very much appreciated.

Also, I believe I will now have to dig into the CO and A/F mixture.

I'm thinking I should probably start a new thread if/when I have questions about them?

Andy

Andy,

glad to hear that the issue seems to be sorted. Well done.

I would prefer to continue here as the story of the car now is known here which is more helpful instead of reinvestigating all the details again. I already posted here earlier the instructions on how to check the sensor plate height and injection start / fuel pump start when the sensor plate is lifted slightly. Check these settings if they're fulfilling the specs. Also check the CO value on a certified gas tester as specified by Porsche (before catalyst if present, detached vacuum of the dizzy, warm idling engine, etc.).

Report these points here and we will see which steps have to follow...

Thomas

Thanks Thomas, as my son's car has also been having an issue that we finally fixed yesterday, today was the first day in a couple months that I was not required to spend at least a couple hours working on a car, so I took today off.

I'll try to start on the sensor plate tomorrow.

Andy

The joy of sorting out the issues that couldn't solved by pro's and instead by yourself is priceless. Enjoy the car and sharing time with the family. Hope you aren't affected by the Franklin bush fire...

Thomas