Another try at adjustable WUR sketch, it actually worked!
 

http://forums.pelicanparts.com/uploads/WUR 1980 SC.gif
Finally, it worked! Here is the inside of a 1980 SC WUR. Does anyone know if the small adjustment screw inside is used for adjustments? I have not done the drilling and tapping in the plug which allows adjusting from the outside, so, picture this WUR without the modification. Do other years have the internal adjustment screw and what is it for? :rolleyes:

Bump!http://www.pelicanparts.com/support/...sun_smiley.gif

My 79 WUR did not have that set screw. Very interesting. The screw would only allow for modification of the cold start pressure. Because as the bi-metallic bar heats up, it's effect on pressure is removed, and control pressure is determined soley by the spring.

The external adjustment screw would work much better,because you could adjust it while the car was running and with a CIS pressure tester connected.

1980 WUR Mistery
 

Has anyone else seen this internal adjustment screw in a WUR? :confused: If so, what year? I agree with Bill that the external plug-modification and the fuel pressure gauge is the preferred way, still, there must be a reason for the internal screw. Anyone?:rolleyes:

I agree with Bill that only the initial cold-start pressure would be adjusted. This could be advantageous if some other components in your fuel system aren't operating 100%, perhaps like being able to compensate for altitude. Do you have a pic of the entire width of the WUR to attach as well?
Ryan

Hi 007: There is not much more width on the right side. The whole thing looks like a regular WUR, except for the internal adjustment screw. The '78 - '79 have the same WUR, 1980 SC has its own model and '81 - '83 are again interchangeable. I would like to know if the '81 - '83 also have an internal adjustment. Anyone?:rolleyes:

My Euro '80 SC still has its original WUR, and here's an internal adjustment screw that I found to be quite useful, and the only way I have found to adjust the WARM control pressure.

For an '80 SC, take a look at the end of the WUR that does NOT show on the picture in the original message of this thread. The drawing for an '80 SC is different -- there are TWO springs that influence the cold pressure, and there is a vacuum port at the bottom of those springs. Between the two springs is a diaphram that is the top of the vacuum chamber for the vacuum port. In the center of the diaphram is a hollow machine screw and a nut. Inside the hollow machine screw is an adjusting screw with a 3-4 mm internal hex fitting. This adjusting screw adjusts the compression on the upper spring, thus adjusting the pressure on the operating rod that pushes upward on the fuel diaphram, thus adjusting the WARM pressure of the WUR. To adjust, remove the spring plate temporarily (so the WUR thinks it is WARM), reinstall the WUR, turn on the fuel pump, and check the pressure. Remove, disassemble, adjust, and repeat until you get the pressure where you want it. In about 3 tries you can get the WARM pressure right on the spec. Put the spring plate back in, adjust it for COLD pressure, and you are set.

In this manner, the WARM and COLD pressures are adjusted independently and have no effect on each other. The COLD pressure is controlled by the bending of the horizontal spring plate. When the WUR is "warm", the spring plate no longer holds the spring (at the right) down, so the compression of the vertical spring controls the WARM pressure.

I've never heard anyone else mention this adjustment screw in my 20 years with this car. My SC does not have the adjustment screw in the long spring plate as shown in the picture.

Brain,

Do you have any pictures? I didn't notice that warm pressure adjustment in my '79 WUR, but maybe I overlooked it, or maybe it's only on the '80 WURs.

Nope, no pix. It has been years since I "discovered" this when poking around inside my disassembled WUR. And its presence does NOT jump out at you. I stared at it for quite some time before I realized what I was looking at. In fact, I took it apart BEFORE I realized it was an adjustment screw!!

"Gunter" describes his picture in the original message as from an '80 SC. Not really -- that picture is from an earlier WUR. The original one in my Euro '80 SC is like the ones pictured in Pelicans catalog for 78-79, and 80, and in parts diagram 1-7-2. The key difference is the vacuum port under the spring at the right side of the picture in Gunter's message. On Pelicans pictures, you see it externally as a vacuum line connection on the left side of the WUR. If you have that external port, it is possible that you have the same adjustment screw that I found in mine. But I wouldn't guarantee it, because I've never heard it mentioned or drawn anywhere else before in 20 years of watching.

If you're interested, I can scan a picture I have of the cross section of the WUR that shows the vacuum port, and could in more detail describe how I think it works and where the adjustment screw is. But that would have to wait until tomorrow when I can get to a scanner.

Brian Haggard, Chester, VA

Because of poor idling following initial start-up, I've been investigating the WUR on my '86 930. Tech article, if I recall correctly, says resistance should be 22-26. When checking mine several times, I always come up with 45-46. Does this mean mine is "bad" and is non-adjustable ?

Let's solve the WUR mistery
 

Brian, please, post a sketch. My '80 SC is US, not Euro. The WUR on my 3 Liter stock is BOSCH # 0 438 170 009 and it runs beautifully. Now, I obtained a used WUR from an '80 SC with the identical BOSCH number and took it apart. It does not have the "plug modification" as shown in my sketch, but it does have the internal small adjustment screw as shown. It has one round, main spring designed to work against the flat bi-metal plate which, when warmed up, will move the small plunger on the diaphragm and affect fuel pressure. It also has the outside vacuum nipple but I don't have a hose connected. The 1980 SC US stands alone; according to Porsche, and the Pelican catalog, it has its own WUR and cannot be interchanged with other SC-years. Brian mentions two springs but without a sketch I don't understand. Where is this parts diagram 1-7-2? Also, when checking for resistance across the heater element, I get none on both engine- and spare WUR, just closed circuit. Some have mentioned 20 Ohms? Let's get to the bottom of this, please:confused:

This is a sketch from a WUR (What year?) submitted by someone earlier. It shows details of the plug modification but does not show the nipple for the vacuum line or state what year it is. http://forums.pelicanparts.com/uploa...WUR sketch.gif

For a reference, I have a 80 Euro SC, the part number of the WUR is 911.606.105.09. It has a vacuum line attached to it.

There were two main types of WUR's for SC's.

First style was for k-basic and had the lower vacuum chamber, and two springs. (All euros and '78-'79 USA)

The second style was for K-lambda, and did not have the lower vacuum chamber. Only one spring. ('80-'83 USA)

The difference in the USA '80 and '81-'83 is just a slightly different warm-up control pressure curve as shown in the charts in the Bently manual.

All of the SC WUR's have a vacuum port on the top. Only the k-basic WUR has the vacuum port on the side, for full throttle enrichment. K-lambda uses the frequency valve for full throttle enrichment, so it does not need the lower vacuum chamber.

Here is a pic of the insides of the k-basic style WUR. The smaller spring sits inside of the larger spring. This is a USA '79 WUR, but I use it on my '80 Euro. (both k-basic)

The screw which Brian mentioned is on the center section of the lower vacuum chamber which can be seen on the far right.

Thanks 1980 SC! Great stuff! That makes sense. What resistance do you read across the heater element?:rolleyes:

I just checked, and my two k-basic WUR's read 23 and 25 ohms. By viewing the warmup control pressure graphs in the Bentley manual, you can see that they've changed how quickly the bi-metallic strip heats up, so different years should have slightly different ohm readings.

Rob
1980SC

1980SC. How do you get the reading? I put my leads on the outside electric connection ( 2 pins) of the WUR and get a closed circuit. How do you obtain approx. 20 Ohms? Where do you put your leads? Cheers. :)

Great picture, 1980SC!!

The attached picture is a cross-section of a WUR that is almost identical to my '80 Euro SC. The only difference is that mine has an external tube at #9 that is hooked to a vacuum line. That vacuum line goes to the thermovalve.

In the picture, the WUR is in the "WARM" mode - the bimetal spring has lifted off the top plate (the plate above spring #7). When COLD, the bimetal spring presses DOWN on that plate, compressing the springs -- #7 and the unnumbered INNER spring -- allowing more gas to bypass from #6 to #5, lowering the control pressure, thus enrichening the mixture.

1980SC's picture shows the innards quite well. #10 is a rubber diaphram. It is sandwiched between two washers that have their perimeters turned away from the diaphram as shown in the drawing. The two washers are held together by the part that contacts the lower stops (#11) in the down position and pushes up on the INNER spring. The adjusting screw that I found runs vertically through the center of that part (lower right of 1980SC's picture), and can lengthen or shorten the overall height of that part. This length adjustment results in variable upward pressure on the INNER spring, thus adjusting the pressure on the upper diaphram (#4). The upward pressure on #4 varies the fuel pressure, thus varying the mixture.

I've seen that diagram before, and I've always been confused by it. It says that the full load diaphram is at the idle position. But for it to be in the full-load position, and to reduce control pressure, then the intake manifold pressure would have to be greater than atmospheric. That can only happen with a turbo.

There are two opposing forces on the lower diaphram: Upward force from vacuum at #3, and downward force from the inner spring. With high vacuum at idle, the vacuum is stronger than the spring. As engine power goes up and vacuum goes down (intake manifold pressure approaches atmospheric), the vacuum pull UP is dimished and the spring pushes the diaphram DOWN, enrichening the mixture.

What perplexes me is the source and strength of the vacuum signal. The port on the throttle valve is above the throttle plate so the range of the signal is smaller than if the port were below the plate. I then leave it to faith that Porsche and Bosche measured the signal and properly balanced it with the inner spring rate to achieve the desired movement of the lower diaphram.

adjustabe wur idea
 

i think that the wur works as follows:
the heater heats the bimetal at a constant wattage. when the outside air is cold, as drawn in from the vacuum ports the heater can only expand the bimetal a certain distance, which causes the pressure to be increased which causes a richer fuel supply. as the outside air temperature increases, the differential temperature decreases and the bemetal can expand to close off the pressure and lean out the mixture.

i believe that by adding an adjustable resistor (AR) to the power feed to the wur, 0 to 75 ohm should do it, then you will effectively create an adjustable wur without having to remove and drill the wur. i think that at 0 ohms on the AR the heater will be full onl and cause the bimetal to lean out the mixture unless the outside air is very cold. as the AR is moved to 75 ohms the heater will esssentially be de-energized and cause the outside air to contract the be-metal and enrichen the mixture.

just a thought and worth a try if you are looking for an adjustable wur.

gary




if the above is correct i think that by inserting anadjustable resistor in the power feed to the wur, that you could make an adjustable wur without having to remove or do any work on the wur. because if you reduce the current flowing to the heater the bimetal will close tighter against the pressure port which will enrichen the mixture. by lowering the resistance in line with the heater the heater will increase the temperature and cause the wur to lean out the mixture.

All that would do is slow down the rate at which the WUR leans out the mixture.

Outside air isn't drawn into the WUR, and outside air temperature has nothing to do with the operation of the WUR. Once the bi-metal lever is heated up either by the heating element or through engine heat, it no longer has any effect on control pressure.

what purpose is the heater?
 

i think that the wur is more complex than that. i dont think it relies on force balance to achieve the mixture adjustment. i believe that since the heater is always operational, ( at least on my 1975) then the element is always being heated by this device. that made me think that there is a reason for this heater to be energized when the car is running.

if the engine heat was the method of heating up the bimetal then why would the heater be necessary as the engine heat or lack of heat would perform the same function, i.e. when the engine is cold the bmetal would enrichen the mixture when the engine is warm the bimetal would lean out the mixture.

the wur is more sophisticated than that, and i think that by using the heater a very innovative method of dynamic fuel mixture adjustment is occuring using differential temperature caused by the outside air and by the heating element. if this is not the case then the system would use a simple warm up thermostat to adjust the fuel after the engine warms up without needing the heater or all of the diaghrams and chambers.

that is why the wur is so confusing and can cause so many problems. if the heater is not working you will always be rich, try disconnecting the connection to the the wur and take it for a drive i would bet that no matter how long you drive (maybe in a very warm cllimate) the car will run rich. then reconnect the cable and see how it looks.

full power on the other hand to the wur only allows the wur to lean out the mixture when the outside air temperature overcomes the heater and the bimetal moves to the full lean position.

i may be wrong but i think that the people that designed this device were way ahead of a simple warm-up regulator.

gary

Yes it would, but it would take much longer for the mixture to get leaned out.

There is no outside air flowing through the WUR via the vacuum lines. If it were to do so, it would be called a "vacuum leak" and would need to be fixed. Try blowing into one vacuum line and see if you get air out the other. If you do it's because the internal diaphram is torn, not because it's suppose to work that way.

Your hypothesis about how the WUR works is wrong.

Old Post: Picture of WUR Internal Set Screw
 

Here is a picture of the internal set screw on the bimetal arm inside the WUR, from my 82 SC. The part number is 0 438 140 090, and it has one vacuum connection at the top that goes to the throttle body, but nothing at the base near the main spring.

The set screw and electrical contact are actually on a second, smaller bimetallic arm.

You can also see in the yellow circle that there is an electrical contact switch, which I believe interrupts the heater circuit once the bimetallic arm has bent fully. Perhaps the set screw is to adjust this temperature point and therefore the warm control pressure.

Can anyone explain how this screw would affect the operation of the WUR?

http://forums.pelicanparts.com/uploa...1061953497.jpg

Olivier

I suggest that you put this question, with pic, as a seperate thread on the board if you get no answer. The sc's have different WUR's for '78-'79, 1980 stands alone, and '81-'83 has a different one again. On my '80, the vacuum line isn't even connected to anything and the WUR works fine. I noticed the same adjustment screw on the inside and assume that it is for calibration. Good luck.

Wow!

I have to agree with Bill that the WUR is a simple device. It is just a back pressure device. The bimetal strip counters the spring force when cold and the heater relieves the spring force as it is heated. With a fuel pressure gauge, one can monitor the control pressure from a cold start to see that it gradually rises. It does not take long. The vacuum (‘76-‘77 and ‘78-‘79), depending on how it is applied (top or bottom of spring-diaphragm), will affect the spring force too. On the ‘78-‘79 the vacuum connection is on the side, opposing the spring force to heal reduce control pressure during cold starts. That vacuum source is interrupted via the thermo-valve. The’80 did not have an atmospheric pressure (intake pressure) tap; the 81-83 did have an atmospheric tap on top of the WUR. These don’t really have much accept on the WUR. Atmospheric connection was meant to compensate for changes in atm pressure changes (barometric and elevation changes). I think it would have top be a large change for one to see that the “vent” port does work. Or try blowing into it. There is no air flow through the WUR. Key word: FLOW.

Remember the lambda cars had lean-rich adjustment via the frequency valve.

It is likely that the heating element does short out as the bimetal strip rises per the earlier suggestion related to the little screw on the stripe assembly. Think toaster. Or it just hovers at some threshold between to much heat and just enough heat due to the current flow to it. Resistance on the heater is what creates the heat right? So a higher resistance may increase the ramp rate from “cold start pressure” to warm control pressure. Zero resistance is bad and so is too high of a resistance.

It’s really not that precise, but it works and a couple of pounds delta in the control or cold pressure will not make the CIS misbehave.

When warm the control pressure is controlled solely by the spring. That’s it.

You want variable control pressure? How about a PID loop with a digitally controlled back pressure regulator with logic or human interface. Not really practical.

Just get your cold pressure within spec (adjustable WUR as others have done makes it easy) and your warm pressure in the range as suggested by the readily available P-T charts for your CIS engine. If your spring or diaphragm are shot, get a new WUR or rebuild it, or look me up and I’ll build you a PID Loop controlled setup. Price discounts for Pelicans.

Souk -

Could you explain a little more on ways to make warm control pressure adjustable on the go? I occasionally change my warm control pressure, but it requires disassembling the WUR as Brian Haggard mentions on the first page of this thread.

http://forums.pelicanparts.com/uploa...1062004991.jpg

I'd love to be able to make adjustments on the fly, but I haven't been able to think of a way to do that??

Thanks,
-Rob
1980sc

The small set screw inside the WUR changes the sensitivity of the second (smaller) bimetal strip in opening the set of contacts visible in the photo I posted. At the plug connection on the outside of the WUR, I get 25 ohms with these internal contacts closed and 10 ohms with them open. It seems that this is the way the WUR regulates the warm control pressure, sort of like a simple thermostat to reduce the amount of resistance through the larger bimetal strip as everything warms up.
Actually, now that I think about it again, it is probably to alter the speed that the WUR moves the system from cold to warm control pressure. The small bimetal strip is not heated, so it is only affected by the ambient temperature inside of the WUR, which would be mostly dependent on the outside air and engine temperature. A closed internal contact during warmer conditions would heat the larger bimetal strip more quickly, so the car would not run rich for as long. In colder conditions, the large bimetal strip will get less resistance and the car will take longer to go from the enriched to the lean state for warm running.

Olivier

Methinks you are right about the resistance controling the duration of the warmup cycle. But it does not control the fuel pressure once the cycle is complete. At the end of the warmup cycle, the bimetal strip has bent upwards far enough that it no longer has contact with the spring mechanism, so it no longer has an effect on the pressure. Beyond the warmup cycle, the bimetal strip probably still needs a little heat to keep it bent upward and "out of the way".

I agree...I think the only way to affect warm control pressure would be to change the spring or "adjust" its shape, which would be hard to do accurately and hard to reverse. I set my set screw so that I would get the slow warm up cycle below about 50 degrees, but I will probably have to tweek it more when it gets colder. It is easy to check the switching point based on ambient temperature just by checking the resistance at the plug connection.

Agree. Messing with spring rates is not a particularly wise thing to do. It is hard to argue that Porsche/Bosch did not do it right. Once the "cold" and "warm" pressures are set, things run pretty well and I don't think we can improve on it.

More great posts and technical discussions from the past.

What is the effect of venting the vacuum to atmosphere disabling the diaphraghm ?

http://forums.pelicanparts.com/attac...sketch-wur.jpg