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Cold starts every time - just won't run until it warms
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Gatornapper  



Joined: 23 Oct 2021
Posts: 294
Location: VA

PostPosted: Fri Jan 07, 2022 8:16 am    Post subject: Another question: Reply with quote

I've read in a number of places that the WUV/WUR/CPR regulates the controlling fuel pressure in the Fuel Distributor even after the engine warms up during normal engine operation.

My question is simple: how can it do this? I see no modulating input or controls to the WUV to cause it to be anything but open or closed. Once the WUV module itself is warm from engine heat, it seems the valve can only stay in the closed ("B") position.

It is like a single pole light switch - either open or closed. Cold, it's open. Warm, it's closed.

So does it truly modulate fuel pressure in the F.D. under normal operation, and if so - how?

"Enquiring minds want to know..."

GN
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'87 944 S, looks & runs like new - sold my sweet 931; '76 914 2.0 mostly restored; 2011 Porsche Cayman S in Meteor Grey, 3.4L, Softronics ECU tune 355+hp , PDK w/Sport Chrono. Got this thing for Porsche's.......
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Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1353
Location: Washington DC area

PostPosted: Fri Jan 07, 2022 9:08 am    Post subject: Reply with quote

It's not binary. it's a disc that is controlled by the temp of the bi-metallic spring. As the spring heats up, it allows some pressure to bleed off between your L&R pipes lowering the control pressure way back in the fuel distributor.
This bled off fuel is dumped back to the fuel tank.
It's the opposite of a needle and seat in a carb.
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1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
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Gatornapper  



Joined: 23 Oct 2021
Posts: 294
Location: VA

PostPosted: Fri Jan 07, 2022 12:06 pm    Post subject: Reply with quote

Chuck - PBPWM again.

But once the engine is at full operating temp, there a full 12v to the heater of the bi-metallic spring? And doesn't engine heat keep the spring in the fully up position, keeping the valve closed? I thought that once the engine was warmed up, a full 12v went to the heating coil around the spring.

I do understand the bleed-off of the control pressure.

So you are saying that during normal engine operation, the bi-metallic spring is constantly opening and closing the valve?

Thanks,

GN

Fifty50Plus wrote:
It's not binary. it's a disc that is controlled by the temp of the bi-metallic spring. As the spring heats up, it allows some pressure to bleed off between your L&R pipes lowering the control pressure way back in the fuel distributor.
This bled off fuel is dumped back to the fuel tank.
It's the opposite of a needle and seat in a carb.

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'87 944 S, looks & runs like new - sold my sweet 931; '76 914 2.0 mostly restored; 2011 Porsche Cayman S in Meteor Grey, 3.4L, Softronics ECU tune 355+hp , PDK w/Sport Chrono. Got this thing for Porsche's.......
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924RACR  



Joined: 29 Jul 2001
Posts: 8794
Location: Royal Oak, MI, USA

PostPosted: Fri Jan 07, 2022 10:56 pm    Post subject: Reply with quote

Yes, the engine heat itself will warm the WUR too, the electrical circuit just speeds the process up. The bimetallic strip inherently actually works without electricity - it's solely a function of temperature. The wire wrapped around it just heats it faster than the conducted heat from the motor, matching the rate at which the engine combustion chamber warms up (more or less).

But yes, that valve has to always be cracked somewhat - because consider that the control pressure, set by the WUR/CPR, is always lower than the pressure of fuel delivery from the pump (determined by a basic spring/shim stack pressure regulator in the side of the fuel distributor, right where the fuel comes into the fuel dizzy). So it should never close.

But to say that it's always moving around during operation is not entirely accurate; it can move, and will with temperature, but certainly not fast, and for all intents and purposes once the engine's up to temp it should be steady.

Well, except for the fact that the inside of the WUR is also indexed to boost, and so that will impact the position of the diaphragm too...
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Gatornapper  



Joined: 23 Oct 2021
Posts: 294
Location: VA

PostPosted: Sat Jan 08, 2022 2:14 am    Post subject: Reply with quote

Vaughan -

I GET IT! Removing and rebuilding the WUR next!

Thank you and the other guys for helping me to understand!

GN

924RACR wrote:
Yes, the engine heat itself will warm the WUR too, the electrical circuit just speeds the process up. The bimetallic strip inherently actually works without electricity - it's solely a function of temperature. The wire wrapped around it just heats it faster than the conducted heat from the motor, matching the rate at which the engine combustion chamber warms up (more or less).

But yes, that valve has to always be cracked somewhat - because consider that the control pressure, set by the WUR/CPR, is always lower than the pressure of fuel delivery from the pump (determined by a basic spring/shim stack pressure regulator in the side of the fuel distributor, right where the fuel comes into the fuel dizzy). So it should never close.

But to say that it's always moving around during operation is not entirely accurate; it can move, and will with temperature, but certainly not fast, and for all intents and purposes once the engine's up to temp it should be steady.

Well, except for the fact that the inside of the WUR is also indexed to boost, and so that will impact the position of the diaphragm too...

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'87 944 S, looks & runs like new - sold my sweet 931; '76 914 2.0 mostly restored; 2011 Porsche Cayman S in Meteor Grey, 3.4L, Softronics ECU tune 355+hp , PDK w/Sport Chrono. Got this thing for Porsche's.......
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Gatornapper  



Joined: 23 Oct 2021
Posts: 294
Location: VA

PostPosted: Tue Jan 11, 2022 11:10 am    Post subject: I lied...... Reply with quote

Well, not really. Change in plans.

CIS pressure testing gauge/system arriving any day.

Going to test all CIS pressures according to factory manual and see what's really going on.

If pressures are within specs, I'll not touch the WUR. If they aren't, I'll give it my best at rebuilding it.

GN
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'87 944 S, looks & runs like new - sold my sweet 931; '76 914 2.0 mostly restored; 2011 Porsche Cayman S in Meteor Grey, 3.4L, Softronics ECU tune 355+hp , PDK w/Sport Chrono. Got this thing for Porsche's.......
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Fifty50Plus  



Joined: 28 Feb 2008
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Location: Washington DC area

PostPosted: Wed Jan 12, 2022 5:36 am    Post subject: Reply with quote

Good plan! The CIS tester will show whether the WUR is working correctly.
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car
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Gatornapper  



Joined: 23 Oct 2021
Posts: 294
Location: VA

PostPosted: Wed Jan 19, 2022 12:00 am    Post subject: Reply with quote

Got very good CIS Pressure tester - so easy to use. Gotta rebuild the WUV.

Only good news is my fuel pump is putting out 78psi.

Cold engine CIS pressure is 75 psi and does not change as engine warms up. WUV is not modulating pressure at all.

Shop/garage is frigid, but may try to pull WUV in next few days.

Two questions:

1. What is the correct # for an early 1980 (mfg. 6/79) 931 WUV/WUR? I'm finding 3 numbers: 063133404, 063133404X, and 477133403X. Or do I just have to wait until I get the WUV out and see what number is on it?

2. I cannot find a rebuild kit for these numbers. Does anyone know of one?

BTW - with the WUV not working, hard to believe engine starts fine and runs fine cold from the start. Wondering how it is doing that? It does overheat though as mixture is far too rich. So I don't run it long.

TIA,

GN
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'87 944 S, looks & runs like new - sold my sweet 931; '76 914 2.0 mostly restored; 2011 Porsche Cayman S in Meteor Grey, 3.4L, Softronics ECU tune 355+hp , PDK w/Sport Chrono. Got this thing for Porsche's.......
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Gatornapper  



Joined: 23 Oct 2021
Posts: 294
Location: VA

PostPosted: Thu Jan 20, 2022 9:27 am    Post subject: Reply with quote

Ok, got the WUR out today. Was pretty easy except for that bottom bolt, which took over an hour even with my homemade 1 1/2" long 5mm allen wrench in my 5mm 1/4" socket.

As all who've done this know, the main problem was the heater valve and hose blocking access to the bolt.

Found my WUR is 0438 140 062 with vacuum. Seems to be the one for all 924 Turbos.

Found and ordered rebuild kit from Germany on eBay for $100 US and got it but won't be here for 3 weeks.

Meanwhile I think I'll try rebuilding the WUR w/o the kit and see what happens. Coil is good at 23 ohms. Only when I install it, I won't put in the bottom bolt until it's proven to work properly.

GN
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'87 944 S, looks & runs like new - sold my sweet 931; '76 914 2.0 mostly restored; 2011 Porsche Cayman S in Meteor Grey, 3.4L, Softronics ECU tune 355+hp , PDK w/Sport Chrono. Got this thing for Porsche's.......
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Gatornapper  



Joined: 23 Oct 2021
Posts: 294
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PostPosted: Thu Jan 20, 2022 11:12 am    Post subject: Reply with quote

Can anyone explain to me how the vacuum part of the WUR works?

Does more vacuum cause the WUR to lower the control pressure, and richen the mixture?

GN
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'87 944 S, looks & runs like new - sold my sweet 931; '76 914 2.0 mostly restored; 2011 Porsche Cayman S in Meteor Grey, 3.4L, Softronics ECU tune 355+hp , PDK w/Sport Chrono. Got this thing for Porsche's.......
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2596
Location: MI

PostPosted: Fri Jan 21, 2022 5:02 am    Post subject: Reply with quote

Gatornapper wrote:
Can anyone explain to me how the vacuum part of the WUR works?

Does more vacuum cause the WUR to lower the control pressure, and richen the mixture?

GN


It’s more for boost than vacuum..

More boost/pressure, makes the spring in the WRU push a bit less on the diaphragm valve, let’s more fuel flow through WUR, lowers control pressure on top of the piston in the fuel distributor, less force resisting the movement of the airplate, airplate travels farther moving the piston farther exposing more area of the metering slits, riches mixture..

Boost pressure sensing WUR riches mixture when air pressure is applied to that port..

WUR basically controls how hard it is to move the airplate..

With lower control pressure the airplate will deflect more for any given amount of air vs high control pressure..
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Gatornapper  



Joined: 23 Oct 2021
Posts: 294
Location: VA

PostPosted: Sat Jan 22, 2022 12:01 am    Post subject: Reply with quote

Eddie -

THANK YOU!

I discovered that last night when I put a tube on the middle section of the WUR and sucked on it - noting immediately that the diaphragm indeed did not move.

Then I blew pressure on it, and noted immediately that the diaphragm LOWERED the place where the center/smaller spring hits only - not affecting the larger spring.

I instantly thought - "this is not vacuum controlled, but must be boost controlled."

But then I was confused because the WUR is referred to as a vacuum-controlled WUR. Clearly it is not.

Wondering why it is mis-named......??????

Thanks again for the explanation.

GN

Fasteddie313 wrote:
Gatornapper wrote:
Can anyone explain to me how the vacuum part of the WUR works?

Does more vacuum cause the WUR to lower the control pressure, and richen the mixture?

GN


It’s more for boost than vacuum..

More boost/pressure, makes the spring in the WRU push a bit less on the diaphragm valve, let’s more fuel flow through WUR, lowers control pressure on top of the piston in the fuel distributor, less force resisting the movement of the airplate, airplate travels farther moving the piston farther exposing more area of the metering slits, riches mixture..

Boost pressure sensing WUR riches mixture when air pressure is applied to that port..

WUR basically controls how hard it is to move the airplate..

With lower control pressure the airplate will deflect more for any given amount of air vs high control pressure..

_________________
'87 944 S, looks & runs like new - sold my sweet 931; '76 914 2.0 mostly restored; 2011 Porsche Cayman S in Meteor Grey, 3.4L, Softronics ECU tune 355+hp , PDK w/Sport Chrono. Got this thing for Porsche's.......
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Gatornapper  



Joined: 23 Oct 2021
Posts: 294
Location: VA

PostPosted: Sat Jan 22, 2022 12:17 am    Post subject: Reply with quote

Ruben Simmank in Germany is my source for the rebuild kit for the WUR, and sent me a complete set of clear instructions on the rebuild for this boost-controlled WUR. I'll check with him to see if I can post them here as they are copyrighted.

Meanwhile I have this question (yes - my questions are endless): The interior and every part of my WUR looked pristine. Like new. I could find nothing that would interfere with its proper performance. Not one sign of fuel crud on the fuel side of the thin disc that adjusts the control pressure, no sign of dirt (of course - it is a well-sealed unit) or wear anywhere. Both ports clear and open, no debris in intake port.

So I'm wondering WHY the WUR wasn't working properly. At first, it was frozen closed. Then I put 100psi of air pressure on the center (return) line with the other end (source from fuel dist.) open/disconnected.

This as intended did open the valve. But then it was frozen in the open position, not modulating the control pressure. After disassembly, I could find nothing that would cause this. The thin disc that closes the valve is like new.

Today I will soak all the appropriate parts (NOT the heating element & bi-metallic bar) in carb cleaner, thoroughly and gently clean, and re-assemble. As one article said most of these WUR's simply need a good cleaning, I'm hoping mine will work fine after my cleaning & rebuild. If not, I'll do it again when the rebuild kit arrives from Germany.

Wondering if any of you might know why the WUR froze in the full open position?

Sorry for all the questions. It's just the way I'm wired.

GN
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'87 944 S, looks & runs like new - sold my sweet 931; '76 914 2.0 mostly restored; 2011 Porsche Cayman S in Meteor Grey, 3.4L, Softronics ECU tune 355+hp , PDK w/Sport Chrono. Got this thing for Porsche's.......
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Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1353
Location: Washington DC area

PostPosted: Sat Jan 22, 2022 3:37 am    Post subject: Reply with quote

Gator,
When I was troubleshooting my NA WUR on my race car, I tried rebuilding, replacing, re-replacing (I plugged in 3 different WURs over time) to find out why the control pressure didn't drop. It turned out that the line dumping the excess fuel back to the tank (thus lowering the pressure) was clogged. I cleared that and now it works fine. My guess is that all of the WURs I rebuilt or swapped in were good.
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car
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Gatornapper  



Joined: 23 Oct 2021
Posts: 294
Location: VA

PostPosted: Sat Jan 22, 2022 9:40 am    Post subject: Reply with quote

Chuck -

Of course! Had not thought of that, will check tomorrow.......thank you!

GN


Fifty50Plus wrote:
Gator,
When I was troubleshooting my NA WUR on my race car, I tried rebuilding, replacing, re-replacing (I plugged in 3 different WURs over time) to find out why the control pressure didn't drop. It turned out that the line dumping the excess fuel back to the tank (thus lowering the pressure) was clogged. I cleared that and now it works fine. My guess is that all of the WURs I rebuilt or swapped in were good.

_________________
'87 944 S, looks & runs like new - sold my sweet 931; '76 914 2.0 mostly restored; 2011 Porsche Cayman S in Meteor Grey, 3.4L, Softronics ECU tune 355+hp , PDK w/Sport Chrono. Got this thing for Porsche's.......
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