Seriously, do I really need a WUR?

[Hotwatermusic]

Without getting into the particulars as to why I would, is it possible to start and drive my 83 SC engined '74 911 without power to the WUR? Will I cause any damage if I just pull power to it? I live in Texas and today, for example, it was 80 degrees. It gets below freezing *maybe* twice a year. Does my car really need this thing? I've searched this subject and can't see where anyone has actually asked it.

[timmy2]

WUR=Warm up regulator is a misnomer. (poorly named)
It is actually a constant fuel pressure regulator that compensates for temperature.
Without it your fuel pressure will be far too high. Even when fully heated the WUR lowers/regulates the fuel pressures in the system.
HTH

[Hotwatermusic]

Ah, so that would be a definite no. So how do you know when it's malfunctioning? What symptoms will the car show?

[tazzieman]

Originally Posted by timmy2

WUR=Warm up regulator is a misnomer. (poorly named)

...AKA the control pressure regulator.
I think of it as the engine's analog brain. Primitive, but it instinctively knows what to do.

[timmy2]

Poor cold starts, poor warm starts, poor running, stalling, bucking, won't run, and the list goes on...
Basically everything in the Troubleshooting section here:

CIS Primer for the Porsche 911

[T77911S]

you will not cause damage if you remove power.

you CAN start it with no power, but as the engine warms, it will run very rich. although the WUR is designed to also be a heat sink that warms up from engine temp, it would be extremely slow, and even then, i am not sure it would get hot enough to raise control pressures to where they should be. all the power is doiing is heating a heating element inside the WUR.

this is a VERY crude device. it does not do any real pressure regulation. for instance. if the system pressure dropped, the WUR would not compensate. the control pressure would drop too. thus the need for good system regulation.

[Bob Kontak]

Originally Posted by T77911S

you will not cause damage if you remove power.

you CAN start it with no power, but as the engine warms, it will run very rich.

+1

And confirmed by this bone-head last week.

Ohio to NC in the 911. 65MPH. 15 degrees outside. 17mpg on gas refill after four hours. Normally about 23 unless driving like a little girl then over 25mpg.

Connector to WUR is tired and had slipped off.

I put my hand on the WUR when the light bulb in my head came on and it had warmth but it was in no way hot.

[boyt911sc]

Originally Posted by Hotwatermusic

Without getting into the particulars as to why I would, is it possible to start and drive my 83 SC engined '74 911 without power to the WUR? Will I cause any damage if I just pull power to it? I live in Texas and today, for example, it was 80 degrees. It gets below freezing *maybe* twice a year. Does my car really need this thing? I've searched this subject and can't see where anyone has actually asked it.

Hot,

Why would you do that? Even if you decide to unplug the WUR, a bad heating resistance would be acting similarly. Test and check your WUR. Why are so many people having difficulties with the CIS engines in the cold seasons? I would guess that your WUR's heating resistance is about 10 Ohms (??). Keep us posted.

Tony

[montauk]

Originally Posted by boyt911sc

Hot,

Why would you do that? Even if you decide to unplug the WUR, a bad heating resistance would be acting similarly. Test and check your WUR. Why are so many people having difficulties with the CIS engines in the cold seasons? I would guess that your WUR's heating resistance is about 10 Ohms (??). Keep us posted.

Tony

Tony,
A reading of 10 Ohms is normal for some WUR's at lower temperatures. At least that's what I've found after opening my 072 and another 090. There's an internal switch that switches in the 16.5 Ohm resistor in parallel with the 25 Ohm resistor. Both resistors are in the single heating element. There are three connections on the side of the heating element. The switch is adjustable. In my 072 WUR the head of the adjustment screw faces up so you have to remove it to make an adjustment. With the 090 WUR, the screw head faces down so you only need to remove the bottom of the WUR to access it.

There's photos of both and my guess at the wiring in this thread.
CIS fuel pressure rising too rapidly

What temperature that switch operates at is a question I'd like to get an answer to. I really don't know how anyone can properly rebuild a WUR without knowing the correct temperature.

Dave

[Paulporsche]

Dave,

Do you have a pic of that adjustment screw on the bottom of the WUR? I'm assuming this is the one under the brass plug.

The reason I'm asking is because in all the discussions/work I've done regarding my WUR, along w/ a lot of help from Tony, Ty and many others on this board, I've always heard that this adjustment changes the warm control pressure by adjusting the pin position, rather than by changing the resistance, much as knocking the large plug on the top would alter the wcp.

[montauk]

Originally Posted by Paulporsche

Dave,

Do you have a pic of that adjustment screw on the bottom of the WUR? I'm assuming this is the one under the brass plug.

The reason I'm asking is because in all the discussions/work I've done regarding my WUR, along w/ a lot of help from Tony, Ty and many others on this board, I've always heard that this adjustment changes the warm control pressure by adjusting the pin position, rather than by changing the resistance, much as knocking the large plug on the top would alter the wcp.

Paul,
I don't believe that we're talking about the same item. The adjustment screw that I'm referring to sets the temperature for the second resistor to be switched into the circuit. It doesn't have any direct effect on pressure. My thinking, perhaps incorrect, is that at very cold temperatures, the resistance stays high so the arm bends at a slow rate. This give the engine more time in a rich mode to warm up.

At higher temperatures, the engine needs less time to warm up. At this temperature and warmer, whatever that temperature may be, the switch is closed bringing the second resistor in parallel with the circuit which lowers the overall resistance to around 10 Ohms. At only 10 Ohms, the metal bar will bend faster resulting in a shorter time in a lean mode.

Here's a photo of an 090 WUR with an arrow pointing to the screw I was referring to.

[1982911SCTarga]

There is not much known about the adjustment of the "090" leaf-switch-type WURs, other than that the leaf switches do affect the rise rate of the control pressure regulator from cold to warm operating pressure. I've started threads on this very topic.

For the original poster, as a thought experiment only, you could run without a plugged in WUR, but you would have to "knock the pin" up such that the bimetallic strip is not acting on the diaphragm pin. Thus, your engine would always be at the proper warm control pressure. The downside part would be getting through the first few minutes of a cold start because your mixture would be very lean and likely prone to backfiring (not good for the airbox). This also presumes that everything else (ignition timing, vacuum, etc.) is in good working order. Again, this is a thought experiment only.

Brian

[Paulporsche]

Thanks for clarifying, Dave.

[montauk]

Originally Posted by 1982911SCTarga

There is not much known about the adjustment of the "090" leaf-switch-type WURs, other than that the leaf switches do affect the rise rate of the control pressure regulator from cold to warm operating pressure. I've started threads on this very topic.
Brian

Brian,
Here's my semi-scientific method to find the temperature at which the WUR switches from low power (high resistance) to high power (low resistance). See if it makes sense. Bear in mind that I'm using an 090 that I bought used off of ebay. Maybe it's still got it's factory setting or maybe it doesn't. I'll need a virgin WUR which I understand are hard to come by.

I starting by sticking the 090 in our freezer. When I took it out it was reading 26 Ohms and the temperature of the body, according to my cheapo Harbor Freight IR thermometer, was 56F. I let it warm up and the switch closed dropping the resistance to 10 Ohms when the temperature was about 68F. I guess it took about 30 minutes to warm up. The temperature in our house was about 70F. I repeated this procedure and came up with 68F the second time.

Would 68F make sense as the temperature to switch into high power mode? I imagine it probably does. Anybody else ever measure one?

[1982911SCTarga]

Good stuff. I've also thought that the leaf switch system design might be to promote lower power consumption or longevity. In a conventional two-wire WUR, the power draw is constant. With the leaf-switch WUR, the power starts high and goes low.

The 090s that I've opened up have had the leaf switch screw adjuster painted, so someone among the fine folks at Bosch calibrated those durn things for some reason.

The bimetallic strip/heating component is only there to get the fuel system through the cold start, warm re-start phase and up to the warm control pressure when it does not inluence the diaphragm pin. It is the three to four minutes of getting there that make things interesting. Or fascinating, as Spock might say.

Brian

[patkeefe]

-090 is designed for different warm up rates, in theory. It is for the later model SC with the frequency valve CIS setup.

You can run with it unplugged, but it will require longer warmup, and run rich, as has been previously stated. Local ambient temps at the typical WUR during operating conditions are approximately 140F.

montauk is absolutely correct in his write up above. There are two resistors in the WUR. Glad to see someone else doing a little science project!

[boyt911sc]

1/Rt = 1/R1 + 1/R2

R1 = 16.6 Ohms
R2 = 25.0 Ohms

When both resistances are ON:

1/Rt = 1/16.5 + 1/25
Rt = 10.0 Ohms

When R1 = zero
Rt = 25 Ohms

Tony

[montauk]

Perhaps I misunderstood what you were saying in this thread and in another one. I thought you were implying that if the resistance is 10 Ohms, something is not working. Do you know the temperature the factory sets the element to switch at?

CIS fuel pressure rising too rapidly

Originally Posted by boyt911sc

1/Rt = 1/R1 + 1/R2

R1 = 16.6 Ohms
R2 = 25.0 Ohms

When both resistances are ON:

1/Rt = 1/16.5 + 1/25
Rt = 10.0 Ohms

When R1 = zero
Rt = 25 Ohms

Tony

[montauk]

I just got my brand new in the box 072 WUR for about $300.00. The contacts open/close around 70F. This probably isn't super accurate since I'm measuring the temperature on the outside of the WUR but by letting it warm up slowly, I think it's probably close.

I guess that the thinking was that if the outdoor air temperature, OAT, was around 70F, you don't need to be in the warm up mode (rich mixture) for very long. Switching the resistance from 26 to 10 Ohms provide more power (heat) to the arm causing it to close down the valve much quicker that it will at 26 Ohms. (the Power equals the Voltage squared divided by the Resistance). I guess this was done to improve emissions. Any other ideas?

If you're reading 10 Ohms and the temperature is around 70F or warmer, your WUR is probably working correctly. At least that's my take on what's supposed to happen.

Dave