WUR Question

[Porsche80]

I have a 1980 911SC US and have determined that my WUR is bad. In checking the part number on the exising WUR 0-438-140-090 this part says it goes on a 1983 911SC and the part that should be on my car is 0-438-140-072. Both of these units have a vacuum hookup. My seems to be closed off. Obviously, it seems either part works as this has been in the car since I have owned it (8 years now). So I am trying to figure out what the difference is between the two parts?

Thanks

C

[T77911S]

the 72 is for an 80, the 90 for 81-83.
if you have a single vacuum port on the WUR, that is just a vent, not a vacuum port as on the 76-78. the vacuum port on these provided enrichment for WOT.

[Porsche80]

So if I am reading your response correctly, there is no difference in functionality between the 2 devices. If that is the case is there also no difference in operation -specs?

[javadog]

No, if they were not different in some way, Porsche would not have had two part numbers for the same thing. Get your hands on technical specification book and compare the temperature/pressure curves for each one. I'd look for the correct one. There's a bunch of differences between the CIS systems used in 1980 and 1983.

JR

[Bob Kontak]

Regarding differences, I did find this quote in the CIS Primer in the CIS components section under WUR:

'81 saw a change in the internal resistor configuration for the WUR. A second resistor was added to heat the bimetallic spring, controlled by a bimetallic switch. This allows the mixture to lean out more quickly after start-up,about 2 minutes compared to the former 3 minutes.

Probably cold and warm pressures are a little different, too but I don't have my manuals with me now.

CIS Primer for the Porsche 911

T77911S - If thru 78 there was a vacuum enrichment port for WOT on the WUR and from 81-83 there is a Lambda system WOT enrichment did the 79 and 90 have a WOT enrichment? I know I can find this out if I dig enough - just being a little lazy.

Porsche80 - My US 81 had an "-089" regulator on it which is a Euro. Bought the car in 95 and have no idea why it was installed. Maybe for more fuel flow? All the rest of the hardware is US.. I changed it out in the late 1990's for the -090.

How did you determine it was bad?

[T77911S]

if i remember correctly, the difference is the 090 has some kind of switch on the bi-metal strip inside.
as long as your cold pressures are correct and your warm pressures are correct, i would not be concerned, although i have heard of the 090 warming up too quick. that switch may be some kind of adjustment for that. i have not really messed with the later WUR's.
if you have a 090 that meets the correct pressures, i would use it, for that matter, i would use any WUR that was good and i could make adjustable to meet the specs, unless i needed vaccum enrichment.

[boyt911sc]

Originally Posted by Porsche80

So if I am reading your response correctly, there is no difference in functionality between the 2 devices. If that is the case is there also no difference in operation -specs?

Curtis,

If you compare the slope of the charts for the control pressure versus temperature for both -072 and -090, they are very close to each other in values. Look very closely to the mean value for the control pressures. It has a variance of approx. +/- 10% of the mean value which is very broad. While the -090 WUR has a lower control pressure @ 10°C (1.6 bar median) compare to 1.75 bar median for -072, both WUR's have same WCP @ 3.5 bar.

WUR-072 has a slope of 30.1° (measured from the median points).
WUR-090 has a slope of 32.2°

With a deviation of +/- 10%, the line/curve could over-lap with each other because of the wide deviation range.

Lastly, these two (2) Bosch WUR's have identical components (inside and out) with a slightly lower cold control fuel pressure setting for -090. Similarly, WUR-033 and WUR-045 could be used interchangeably too. I've been using and testing these WUR's on SC engines and found no difference in performance provided they are all in good working conditions.

BTW, Porsche AG did not make these designation numbers on the WUR's. Bosch did.

Tony

[Bob Kontak]

Originally Posted by boyt911sc

Lastly, these two (2) Bosch WUR's have identical components (inside and out) with a slightly lower cold control fuel pressure setting for -090.

Tony - Read post 5 - second paragraph and post 6 - 1st sentence or two. There is a small difference in that the 90 warms up a little faster because of "resistor configuration"

[boyt911sc]

Originally Posted by Bob Kontak

Tony - Read post 5 - second paragraph and post 6 - 1st sentence or two. There is a small difference in that the 90 warms up a little faster because of "resistor configuration"

Bob,

Have you checked, inspected, dissected, tested, evaluated, etc. a -072 and -090 WUR's? What small difference between the these two (2) WUR's have you discovered? The internal parts for both these WUR's are identical as far as my limited knowledge to differentiate them. Please help me find and understand the difference. Thanks.

Tony

[Lorenfb]

"If you compare the slope of the charts for the control pressure versus temperature for both -072 and -090, they are very close to each other in values."

That's the key! It's as simple as that.

"There is a small difference in that the 90 warms up a little faster because of "resistor configuration""

Very minor, and most would never notice a difference.

[Bob Kontak]

Originally Posted by boyt911sc

Bob,
Have you checked, inspected, dissected, tested, evaluated, etc. a -072 and -090 WUR's?

Heck no. I was just pointing out what I read in the CIS Manual which is where I picked that quote up from in post 5.

I also don't know what the resistor configuration difference is. The resistor is the heating element wire wrapped around the strip, right?

Interesting you mentioned the -90 has a lower cold control pressure. Maybe the reason, or part of the reason, for the lower pressure was to offset (through added fuel)?) the one minute shorter transition in warmup of the bimetallic strip vs. the -72.

Again, this is what I have read and that is frankly all I know except for my 15 years of fiddling only with my model - and 13 of the years were before I started getting tuned-up by you guys here.

So I really got nuttin'.

Edit: Regarding the exact difference - let me do some searches as the CIS Manual only mentions the difference casually.

[javadog]

FWIW, the 090 part was first used in 1981. Although the same spec is given for the warm control pressure between the 072 and 090 versions, if you look at the graphs, both the cold and warm pressures for the 072 are .1 bar higher than the 090. Porsche gave a warm up time of +- 2.5 minutes for the 072 and less than 2 minutes for the 090. That's all they had to say about them, when the new one was introduced. It's worth noting that Porsche introduced the new regulator at the same time they introduced the new scheme for acceleration enrichment on the 81 models. Lot's of changes between '80 and '81. Given that there's a .3-.4 bar acceptable range in the control pressure values for either WUR, you can argue that either one would work. I suppose you have to decide how close to "ideal" you want your control pressure to be.

The 83 model has a different O2 sensor and acceleration enrichment unit that prolongs the enrichment during cold running for 25 seconds after the O2 sensor begins working. The stated reason for the change was to improve cold running response and to help with meeting California emissions.

[Porsche80]

After taking the part out of the car, it appears to definitely be a 089 I was able to read all but the 9 but it makes sense since it had a vcuum line which i could not clearly see until removing some duct work, etc.so what is the diff between the 089 and the 072 other than the vacuum

[Bob Kontak]

This page has an 089 for sale on it. I noted earlier that my US 81 had an 089 on it when it should have had an 090.

http://specialtauto.com/porsche-parts/index.html

My guess is that this may have been a common "upgrade" replacement and I am also guessing that warm control pressure may be a little lower (more fuel).

The factory manuals I am looking at do not show the 089. Maybe because they are the US versions? The 1979 had an -069 that started in Jan of 1979 but then was replaced when the 1980 model arrived with the -072.

I will look some more for the -089 pressure graph. I swear I have seen it before. I have the -072 graph if you want me to post it.

The other guys know more than me and I betcha can tell you off the top of their heads.

[Bob Kontak]

Here are the graphs:

[Bob Kontak]

Clearer pic of 072 graph

Interesting the vacuum function on the 089 takes it up to 3.4 to 3.8 bar. Mashing the gas pedal removes the vacuum and drops control pressure down to the 3.1-3.2 range for WOT enrichment I am guessing.

[Porsche80]

I suspect one of the PO's did what they thought was either an upgrade or was troubleshooting a cold start issue. A local in my area read my post and had a 090 that he said was good (at least when it was pulled from the car) and offfered to let me use it to test and it made no difference than the orginal and that is when I discovered that my car had a 089. The vacuum on the side of the WUR that goes into a t-connector then goes to the decel vacuum line, that then runs to vacuum advance and to the back of throttle body (the same line that should have my cruise vacuum tied into?). We hooked the old WUR back up and discovered that the decel line was hooked up to front of throttle body to it appears a port not in use and it was not pulling vacuum. Then we discovered that it should go to the back of the throttle body and my issue may be resolved, but will see after a couple of more cold starts, as the engine was warmed up at this point. I am just wondering why the car ran fine up till this time (several years)?