WUR failure question

[hardebeck]

Hi all,

78 SC, freshly rebuilt motor (2 years ago). Ran great until a few months ago, then has become progressively harder to start cold. Bought a CIS fuel pressure tester and system pressure shows 70.5 psi/4.86 bar @ 77F, which is in spec. Problem is when I open the valve on the WUR side of the gage and run the Cold Control Pressure check, the pressure reads almost as high; 69.5 psi/4.8 bar. Did this a couple times, bleeding off pressure before testing again, with same result. Anything else I should do to confirm the WUR has failed or is this definitive? Assuming it's bad, any reason why I wouldn't tackle the rebuild myself? Youtube videos show a reasonably straightforward process and since it's on the internet, it must be true, right?

Appreciate any suggestions, advice, and appropriate rude comments.

[Showdown]

Do a full CIS pressure test and post the results and you’ll get better and more acute feedback. Knowing the status of the full system will better help us in figuring out the precise issue(s)

That said, the mesh filter in your WUR may be clogged- it’s easy to check without disassembling the whole WUR.

Disconnect the WUR and all the fuel lines/hoses and peek into the fuel inlet- you may see debris that can be flushed out with air or acetone.

Rebuilding the WUR is quite easy with patience.

[hardebeck]

Thanks Showdown. The cold and warm control pressure were both nearly the same as the system pressure; 69.5 psi. Based on those results, I didn't think it made sense to try to start the car and check any further pressures. I didn't do a full leakdown test but when I shut off the fuel pump pressure was about 30 psi and decreased gradually to around 20 psi in 7-10 minutes, which seems reasonable. I read a thread that talked about checking the fuel return line for blockage so a clogged mesh filter would seem to be the same possibility.

As I understand the internal workings, there is a rubber diaphragm. If that were to develop a crack or tear, would this be the failure mode we would expect; i.e., control pressure equalizes to be the same as system pressure? It's likely that the WUR is original so it probably makes sense to rebuild anyway.

[boyt911sc]

Hardebeck,

You don’t need a WUR to run your motor if you have a CIS pressure gauge. For the control pressure to equalize as system pressure like in your case, a flow restriction to the return is happening. It could be the WUR, or any where along the return fuel line to the gas tank.

A simple test to locate and identify the location of the culprit is to use your CIS pressure gauge. Disconnect the connection of the CIS gauge to the WUR but still connected to the FD. Test run the FP, and measure the CCP.
NOTE:
The CIS gauge is connected to FD and the line to WUR is disconnected and the valve OPEN. Place the end of the fuel line (gauge) in a suitable container during the test. Read the CCP. Post the value.

If you are familiar how the WUR works, you could test run the motor doing manual adjustments. Keep us posted.

Tony

[hardebeck]

Tony, thank you for your response and apologies if my questions show my incomplete understanding of CIS. When I disconnect the gauge line to the WUR, do I need to plug the open port on the WUR or do I leave it open to atmospheric pressure? I assumed this connection between the WUR and the FD was necessary for the WUR to generate control pressure so the FD can "see" it, so I'm confused as to how the gauge would measure control pressure if it's only hooked up to the FD. I thought that would be the same as reading system pressure.

I've been reading all the info I can find on CIS; the primer, Bosch manuals, Pelican threads, etc., and am committed to learning the basics and nuances as I absolutely love this car. Having owned a couple British sports cars in the past, I've come to appreciate that although Porsche may have its own quirks, they tend to be much better engineered and executed once you understand them!

[boyt911sc]

Originally Posted by hardebeck

Tony, thank you for your response and apologies if my questions show my incomplete understanding of CIS. When I disconnect the gauge line to the WUR, do I need to plug the open port on the WUR or do I leave it open to atmospheric pressure? I assumed this connection between the WUR and the FD was necessary for the WUR to generate control pressure so the FD can "see" it, so I'm confused as to how the gauge would measure control pressure if it's only hooked up to the FD. I thought that would be the same as reading system pressure.

I've been reading all the info I can find on CIS; the primer, Bosch manuals, Pelican threads, etc., and am committed to learning the basics and nuances as I absolutely love this car. Having owned a couple British sports cars in the past, I've come to appreciate that although Porsche may have its own quirks, they tend to be much better engineered and executed once you understand them!

Hardebeck,

Your high cold control fuel pressure problem is caused by fuel flow restriction at the return line system. It might not be obvious to you at this point, but for people who are familiar with CIS troubleshooting would recognize the symptoms right away as restrictive fuel flow at the return line. The blockage is occurring some where between the WUR and FD.

There are simple tests you could perform to identify and locate the culprit/s. In your case the CCP (cold control pressure) and SP (system pressure) are the same in value. Look at it this way, when you close the valve you get the system pressure. You could also get the system pressure by obstructing or restricting the total flow of the fuel by mechanical methods or accidental blockage. Are you still with me?

That is the reason I suggested to test by disconnecting the CIS pressure gauge fitting to the WUR. To answer your question about the disconnected line from the WUR, fuel will not come out. Why? Simply because the inlet to the WUR is the pressure side and the outlet is the low pressure side. However, if the blockage occurs between the FD and the fuel tank, you can not leave it OPEN because there is a likely hood of generating pressure much higher than the system pressure.

Interested to learn and understand CIS? Do this test and see it for yourself. Do not run the motor, just the fuel pump. Tell us if you get fuel coming out from the WUR. Do not accept everything I said, I make mistakes too.

Tony

[hardebeck]

Thanks Tony. It does make sense to me that there is an obstruction between the WUR and the FD. I just need to figure out all the plumbing to identify the return line. I tried your suggestion about running the FP with the gauge disconnected at the WUR and the free end of the hose on the valve side of the gauge running into a jug. Fuel did indeed pump from the FD into the jug, but the gauge registered 0 while it did. Pic attached to make sure I followed your instructions properly.

I'll figure out which hose is the return line next and try disconnecting it and clearing it out.

[hardebeck]

I made progress today but not sure what direction just yet. Here's what I did and found:

-disconnected return line between WUR and FD and confirmed no blockage.

-could see crud in WUR inlet screen so I removed the WUR. Didn't see any way to remove and clean the screen without disassembly so I decided to open it up. The interior was super clean and everything appeared to be in good condition, including gaskets. I removed the bimetallic strip so I could get to the 4 screws that hold the diaphragm assembly (think that's what its called) below the inlet and outlet, but the machined cover plate was pretty well oxidized in place and I was afraid of causing more damage if I tried to remove it, so I settled for multiple rounds of carb cleaner in the inlet and was able to get majority of the crud off the screen. Tried blowing compressed air through the outlet with hopes of dislodging more on the screen but not sure how effective that was. Reassembled and reinstalled WUR with no apparent issues.

Started fuel pressure checks. Here's where it gets a bit funky:

78 911 SC @ 82F outside temp

-System pressure - 71.5 psi / 4.93 bar

Opened valve on WUR side of gauge:

-Cold control pressure - 46 psi / 3.17 bar

Plugged in WUR electric connection:

-Warm control pressure - Started at 46 psi and decreased over 5 minutes to stabilize at 25 psi / 1.72 bar

So, this seems to be pretty much the opposite of what it should be; CCP somewhere around 1 bar and WCP gradually increasing to range of 2.3 - 2.7 per Bentley.

Is it time for a WUR rebuild or should I be checking something else first?

[hardebeck]

Pics for clarity. 99% sure I got everything lined up correctly when I sealed the WUR back up.

[hardebeck]

.....aaaaaaannddd.....as I look at this picture and realize that I could read the lettering on the bimetallic strip when I reinstalled it, I now know why the pressure is going in the wrong direction....

[hardebeck]

I've often found it's helpful to take pictures during disassembly, and it would be even more helpful to remember to look at them during reassembly. Hence my go-to saying/future epitaph; "Experience is what you get when you don't get what you want"

After pulling the WUR and flipping the bimetallic strip over to the correct orientation, I reassembled and ran pressure tests again.

At 84F/29C, not running:
System pressure: 4.9 bar
Cold control pressure: 1.45 bar
Warm control pressure: 3.05 bar after 5 minutes

Depending on how I read the Bentley graph and info in other threads, CCP may be a bit low and WCP a bit high, but at least it's closer to normal than it was. Think I'm going to try the butt in seat test next and see how it feels.

[hardebeck]

Seat of the pants test passed with flying colors.

I'm recapping in hopes that someone reading this thread in the future learns from my travails. Difficult cold start, hesitation and rough idle when I finally got it started, seemed to run OK but not great when warmed up. I assumed some major component was failing or had failed and in the end, it just turned out to be crud in the inlet screen of the warm up regulator. That was the whole problem. The good news in all this is I invested in a CIS fuel pressure tester and learned how to use it (had to machine a new fitting for the WUR since it didn't come with a 12mm female fitting), and troubleshooting forced me to learn more about CIS along the way (although a ways to go for sure). Thanks to Tony and others for weighing in with offers of assistance. Hopefully I can start repaying one of these days.

[boyt911sc]

Originally Posted by hardebeck

I've often found it's helpful to take pictures during disassembly, and it would be even more helpful to remember to look at them during reassembly. Hence my go-to saying/future epitaph; "Experience is what you get when you don't get what you want"

After pulling the WUR and flipping the bimetallic strip over to the correct orientation, I reassembled and ran pressure tests again.

At 84F/29C, not running:
System pressure: 4.9 bar
Cold control pressure: 1.45 bar
Warm control pressure: 3.05 bar after 5 minutes

Depending on how I read the Bentley graph and info in other threads, CCP may be a bit low and WCP a bit high, but at least it's closer to normal than it was. Think I'm going to try the butt in seat test next and see how it feels.

Was the highlighted section above with or without vacuum applied? If the motor was not running, I would assume it was without vacuum applied and slightly higher. Typically the WCP without vacuum for WUR-045 is between 39~46 psi. What is your WCP with vacuum applied? Good job.

Tony

[hardebeck]

Originally Posted by boyt911sc

Was the highlighted section above with or without vacuum applied? If the motor was not running, I would assume it was without vacuum applied and slightly higher. Typically the WCP without vacuum for WUR-045 is between 39~46 psi. What is your WCP with vacuum applied? Good job.

Tony

All readings done with the car off and engine cold, so no vacuum. After driving it and confirming it runs great, I haven’t looked at pressures again but perhaps I should just to get a baseline.

[AlKidd]

Does anyone have a fuel pressure gauge they recommend that comes with enough bits and pieces to be easy to use on the 911? I have steel fuel lines if that makes a difference.

[Showdown]

I use this one and it works out of the box. For testing of the fuel accumulator and fuel filter I had to get some adapters but those were nominally priced.

CTA Tools 3420 K Jetronics C.I.S.... https://www.amazon.com/dp/B008FJXA3M?ref=ppx_pop_mob_ap_share

Adapters can be found on belmetric.com or fittings.space

[hardebeck]

I bought the CIS test kit off Amazon. It came with a bunch of fittings but only 2 with female threads; M8 and M10. The M10 fits the FD but the WUR needs a 12mm. The instructions were incorrect as well; said it came with two M12 swivel fittings but the actual fittings are different. I spent several hours searching for a way to Frankenstein the M12 fitting for the WUR and couldn't find anything. I think it's the first time McMaster-Carr has let me down. Then I realized one of the supplied fittings could be machined into what I needed. I cut off the lower portion of a long M8 male fitting (to the left of the middle fitting in the pic) and then drilled and tapped the hex-shaped shank with the quick release end for an M12x1.5(IIRC) thread (result is the middle fitting in the pic). I have a small metal lathe so it made the job relatively easy. Not sure I could have freehanded it successfully. Hope this helps.

[hardebeck]

Originally Posted by Showdown

I use this one and it works out of the box. For testing of the fuel accumulator and fuel filter I had to get some adapters but those were nominally priced.

CTA Tools 3420 K Jetronics C.I.S.... https://www.amazon.com/dp/B008FJXA3M?ref=ppx_pop_mob_ap_share

Adapters can be found on belmetric.com or fittings.space

That's the same kit I bought. Maybe mine just had the wrong grab-bag of fittings. Appreciate the lead on the sources for new fittings; I'm sure I'll need another I don't have eventually.

[Showdown]

On my WUR (1977 car 033 WUR) there was an adapter from the body of the WUR to the fuel line, removing that enabled me to use the fittings that came with the kit. At first I didn’t realize that and thought the kit was a bust. Try removing the adapter on your WUR…





Alternatively the fittings from fittings.space will work.

[hardebeck]

Originally Posted by Showdown

On my WUR (1977 car 033 WUR) there was an adapter from the body of the WUR to the fuel line, removing that enabled me to use the fittings that came with the kit. At first I didn’t realize that and thought the kit was a bust. Try removing the adapter on your WUR…

Alternatively the fittings from fittings.space will work.

Argh. Yes, that would have saved me several hours. If I had thought to do that I would have seen all the crud in the inlet filter screen right away as well. Didn't occur to me until after I had the WUR out of the car that that fitting wasn't integral. Guess I get to add another item to the "experience" bucket.