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BWW · Joined: 21 Sep 2021 Posts: 58 Location: Idaho, USA

I finally got a fuel pressure tester and hooked it up today between the CIS and the WUR. Regardless of whether the valve to the WUR was open or closed, the meter was pinned. Any ideas on what might be causing this? Does the CIS need a rebuild? I should also mention that I did the 30 second test on the return line to see how much fuel would come out. It was about 500 ml. Thanks in advance for any help.

https://www.flickr.com/photos/196674372@N07/shares/f03EHPNv2Y
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Brent
'81 931 project car

924RACR · Posted: Sun Oct 09, 2022 9:47 pm Post subject:

I did have a WUR fail this way, but pressure that high is higher than even the system pressure should be... makes me think your return line is blocked.

Can you try blowing it out with compressed air?
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Vaughan Scott
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BWW · Joined: 21 Sep 2021 Posts: 58 Location: Idaho, USA

Thanks for the suggestion. I tested this by bypassing the return line to a gas can, but had the same result. It's also clearly related, but the airflow plate hardly opens at all when it's running, and when I press down on it, it stalls out.
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Brent
'81 931 project car

kondzi · Joined: 02 Jul 2018 Posts: 485 Location: Poland/EU

What fuel pump you have there? It’s at least weird. If everything is blocked, then the pressure would max out to the fuel pump maximum.
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Konrad
'89 951 US
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924RACR · Posted: Mon Oct 10, 2022 8:59 pm Post subject:

Even the system pressure shouldn't be that high, seems like to clean that regulator would be a start - though if it's crudded up, probably the whole thing needs a cleaning/rebuild...
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Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
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BWW · Joined: 21 Sep 2021 Posts: 58 Location: Idaho, USA

Not sure about the fuel pump, Konrad, but I think it's stock. Vaughan, that's what I feared. I know the fuel distributors rebuilds can be tricky, but I have found some pretty good tutorials online. I'll go ahead and order the rebuild kit and start there. Wish me luck!
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Brent
'81 931 project car

Beartooth · Joined: 05 Apr 2022 Posts: 206 Location: Roberts, MT

My thought is that it's either the fuel pressure regulator (FPR) or a blocked return line. It shouldn't be anything in the FD itself; I wouldn't bother with that unless you have other problems. I had a problem where my WUR was blocked (the mesh filter before the little valve that regulates fuel flow and varies the control pressure was gunked up and blocking all bit a tiny bit of flow), and that resulted in excessive control pressure, but not more than system pressure. The most you'd ever see as a result of a blocked WUR is system pressure; if you're seeing abnormally high pressure anywhere in the system, I'm not sure how it could be anything other than an issue or blockage with the FPR (keep in mind, it might be possible to install it in such a way that it looks fine but blocks flow), or a blocked return line.

Anyway, definitely start by checking the return line. You can just take the fuel line off, take the gas cap off, and try blowing air through it. You should hear gurgling from the gas tank if it's clear. If that's clear, take the fuel pressure regulator apart and look for blockages. The FD isn't that bad to rebuild, if need be. It's mostly a matter of not losing anything, keeping it clean, and then making sure everything is in the right place and square when you put it back together. But It'd be focusing on the FPR and a potentially blocked fuel line first. Hope that helps.
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1980 931 diamond in the rough

BWW · Joined: 21 Sep 2021 Posts: 58 Location: Idaho, USA

Good idea on the FPR. From what I've read, when these fail they tend to flood the system, which is of course what is happening to me. I will start there. Is there a way to bench test these before I start throwing parts at it? Thanks to everyone for the ideas! This is a great forum.
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Brent
'81 931 project car

BWW · Joined: 21 Sep 2021 Posts: 58 Location: Idaho, USA

So here's the removed FPR. The one o-ring is obviously trashed. Unless I'm mistaken, it should also have something on the end of. I'm not sure if it never had it or it came off in the FD, but there is clearly something amiss...

https://www.flickr.com/photos/196674372@N07/52422049813/in/dateposted-public/

https://www.flickr.com/photos/196674372@N07/52421820304/in/dateposted-public/
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Brent
'81 931 project car

924RACR · Posted: Wed Oct 12, 2022 8:21 pm Post subject:

Hmmm, trying to remember where in there the shims go - which would be the missing part you're wondering about, I think. Though they'll only increase the pressure by compressing the spring more... I wanna say they'd go between the spring and the body of the plug, though it's possible they're in the distributor. Maybe fish around in there gently with a pick, see if you get anything else out?

Either way, it does look a bit crudded-up, won't hurt to clean and reassemble, see how it goes.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
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#25 Hidari Firefly P2 sports prototype

BWW · Joined: 21 Sep 2021 Posts: 58 Location: Idaho, USA

Thanks, Vaughan. Will do. Shouldn't there also be an o-ring on the end of it too?
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Brent
'81 931 project car

924RACR · Posted: Thu Oct 13, 2022 7:35 am Post subject:

I honestly don't recall.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

BWW · Joined: 21 Sep 2021 Posts: 58 Location: Idaho, USA

Okay. Thanks. I will see what I can find online.
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Brent
'81 931 project car

Beartooth · Joined: 05 Apr 2022 Posts: 206 Location: Roberts, MT

I believe the shims go at the base of the spring. There's another piece to come out: it's a piston that slides back and forth, blocking or allowing flow to the return line to control the system pressure. That has an o-ring on the end of it as well. I'm not sure what the best way to get it out with the FD still on the car is; I had my FD off, and it just dropped right out with a tap. If you undo the return line from the WUR and blow some air through it, I think that'll push it out (be careful, or it'll go flying, assuming you're blowing on the right line). One possibility is that the piston could be frozen, blocking return fuel flow. Anyway, I'd think the next step is to get it out, replace the faulty o-rings, and see what that gives you.
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1980 931 diamond in the rough

BWW · Joined: 21 Sep 2021 Posts: 58 Location: Idaho, USA

Thanks, Beartooth. You seem right on the mark. I tried compressed air. Nothing. Then I actually tried closing off the fuel return port and jumping the fuel pump relay. Still nothing. So I took the FD off and tried to slide the piston out with a nudge, but it won't slide out. I'm not sure what's preventing it from doing so, but it clearly catches on something as I try to slide it out. Even levering it with a thin pick does nothing.

https://live.staticflickr.com/65535/52430775813_d1e483db70_n.jpg
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Brent
'81 931 project car