WUR Polarity ???

[patkeefe]

Hi:
Anyone know which terminal is positive and which is negative? I think I posted this before and I don't recall the outcome. Memory is the second thing to go.
TIA, Pat

[timmy2]

Doesn't matter to a resistor.
Neither side is grounded.

[boyt911sc]

Originally Posted by patkeefe

Hi:
Anyone know which terminal is positive and which is negative? I think I posted this before and I don't recall the outcome. Memory is the second thing to go.
TIA, Pat

Pat,

Just like what Timmy2 (Dennis) said, the polarity is not critical. However, this type of electrical plugs maintain a uniform or standard orientation for the ground wire. I really don't know the name for these electrical plugs (maybe Dennis could identify it for us) but one thing I found out, they consistently have the ground (brown wire) at the same terminal. See picture below:



So, if you still have the original engine wire harness, the ground wire for your WUR should be on the right pin (terminal) using your attached picture. Switching the polarity would not have any adverse effect.

Tony

[timmy2]

2 pole female amp connector is what connects to your WUR terminals.
If you need one, these guys have them.
2-Pole Female AMP Connector

[patkeefe]

Stock WUR apart.

[1982911SCTarga]

Pat, what WUR number is that? The guts seem complex and more characteristic of a later lambda-style "090" because of the leaf switches and the three wires to the resistor/heater unit.

I've posted repeatedly about this type of WUR or control pressure regulator because there's some adjustability to it with regard to the switch contacts (but in what way?). I'd like to know more about how this exactly works (note the different resistance values marked on the heater unit).

Mercedes also used this 090-style of WUR.

Brian

[patkeefe]

Brian:
I'll get the numbers in a bit. BTW, the first pictures I posted are an early SC WUR, non-lambda.

It is indeed a later lambda WUR. We are still contemplating how it switches and the extent of the switching, ie, what were the engineers thinking on this one?. Measured resistance is less than it shows...the 16.5 side has 11.9 ohms, and the 26 side has 10.6 ohms. positive 12V is obviously in the center common terminal.

My WUR that I'm using is a 930 model (my SC is a turbo), but the Amp Jr connectors will all be oriented the same, as Tony stated. I fried one before, and don't want to do it again.

I do see a little screw in the leafs. I'm guessing you can adjust warmup time and switch action with this?

[patkeefe]

It's 0 438 140 072. It does have an 090 stamp inside an oval, and also has a 047 stamped on it.

[1982911SCTarga]

Hi, Pat.

I think my resistance values were similar when I was fooling around with one of mine. I also suspect that as you say the leaf switch adjustment has to do with the rate that the unit heats up, but I've been unable to make heads or tails about what exactly happens in terms of electrical flow as it does so or how to optimize it. I've got an EE buddy who might be able to suss it out.

The thing is, those units must have been checked/calibrated/adjusted by the fine folks at Bosch before they went out the door. How was it done?

Brian

[boyt911sc]

Originally Posted by patkeefe

Brian:
I'll get the numbers in a bit. BTW, the first pictures I posted are an early SC WUR, non-lambda.

It is indeed a later lambda WUR. We are still contemplating how it switches and the extent of the switching, ie, what were the engineers thinking on this one?. Measured resistance is less than it shows...the 16.5 side has 11.9 ohms, and the 26 side has 10.6 ohms. positive 12V is obviously in the center common terminal.

My WUR that I'm using is a 930 model (my SC is a turbo), but the Amp Jr connectors will all be oriented the same, as Tony stated. I fried one before, and don't want to do it again.

I do see a little screw in the leafs. I'm guessing you can adjust warmup time and switch action with this?

Pat,

I'll be sending a heater from a -072/-090 WUR to Timmy2 (Dennis) to help me with my investigation. What I found out that many -072/-090 WUR's that failed or exhibited erratic performance have resistance reading of around 10 Ohms (average). While the early CIS WUR's show low or no resistance, it is strange to find that the -072 and -090 WUR's with different bimetallic heaters from the non-lambda WUR's exhibit a consistent resistance of 10 Ohms when they fail to work properly.

Timmy2 has offered to help find the reason for this observation. Dennis is a professional electrician and very capable of finding what's going on in these bimetallic heaters. I'll have one sent to him right away. Anyone who are interested in the test are welcome to participate. Then we could share the finding with everyone.

Tony

[patkeefe]

I pretty much have my question answered, but, I'm going to think about this -090 WUR. I think it has some sort of switching mechanism, and may have something to do with the lambda enrichment I see on the wiring diagram. Tony, are we measuring resistance the same way here? I measured it as you see the photo...left side to common, right to common, across left and right. I recall resistance in parallel being:

1/Rt = 1/R1 + 1/R2; 1/Rt = 1/16.5 + 1/26 => Rt = 10.09 ohms. I think since the positive common is statically feeding both heating elements, we are going to get 10V no matter what, unless we cut the wires from the heating element to eliminate any "backfeed".

I think the leaves are a switch, as Brian suggested previously. This may be a high-medium-low heating arrangement, depending on the circuit being in parallel, one element or series. Maybe tomorrow I can apply a 12V signal to the device and see what it does.

And, if I remember, I'll bring my original non-turbo 78 MY WUR to work and see what it looks like on the inside.

Pat

[1982911SCTarga]

Pat, thanks for tolerating the discussion diversion. I've patiently waited a long time to get some meaningful dialogue going about these later, more exotic, and somewhat little-known-about WURs. If, as we all suspect, there's some adjustments to be had, it would be great to learn how we can use it to our advantage on our cars in setting our rise/run rates.

One other thing. I see you've made your WUR adjustable. When you reassemble it and tweak it in, make sure the bimetallic strip doesn't move inside the housing. I've had problems with this happening even though I've pinned the pin in making the WUR adjustable. It could be related to the stacks of switches that allows the strip a greater chance to move around. Anyway, if you get non-repeatable cold pressures (given similar ambient temps) or odd starting or warm-up/running behavior, split the WUR and check the position of the strip.

Brian

[patkeefe]

Brian:
Don't let me confuse you. I have three WUR's....an original 78 SC WUR, the -090 WUR, and a special 930 WUR which was modded by Brian Leask. I use the Leask WUR, as I have a turbo on my SC; I couldn't get the enrichment with a stock WUR, and I didn't want to add extra injectors.

The original SC WUR was modified by me to make it adjustable for cold control pressure. The -090 is stock, and I was running it on my turbo car along with it's matching fuel head (different cone and metering assembly than the early SC's. The early SC is the WUR in the first picture in the posts.

The turbo WUR is adjustable for cold control pressure, warm control pressure and boost threshhold pressure. That is really a nice setup.

[boyt911sc]

Pat,

I have two (2) -072 and six (6) -090 WUR's and here are the resistance readings I got from measuring across the terminals.

-072 (#1)..................................9.8 Ohms (?????)
-071 (#2)..................................28.0 "

-090 (#3)..................................10.3 Ohms (?????)
-090 (#4)...................................26.0 "
-090 (#5)...................................9.5 " (?????)
-090 (#6)...................................10.0 " (?????)
-090 (#7)...................................10.0 " (?????)
-090 (#8)...................................27.6 " (from a fellow member's WUR)
-090 (#9)...................................25.0 " (from a fellow member's WUR)

Note: Resistance measurement read across the WUR terminals.

1/Rt = 1/R1 + 1/R2 , Rt = 10.2 Ohms (calculation from your WUR)

My dilemma is understanding why Rt (total resistance) measurement differ from the good working units and those (?????) units deemed to be bad (???). Would someone knowledgeable help us understand the discrepancies? Thanks.

Tony

[jeffs9146]

I too am very interested in the results of the later WUR testing! I have an 83sc that I have swapped out the WUR and it is finaly running well! I would like to get my "spare" ready for when I need it!

[LM3929]

any more info on the WUR 090 resistance?

Lorne M.

[boyt911sc]

Originally Posted by LM3929

any more info on the WUR 090 resistance?

Lorne M.

Lorne,

Pat has discovered the anomaly about these -090 WUR's and gave me his calculations written on a piece of paper or napkin at a Garden State Parkway rest area 120 miles away from home. That was the last time I had contact with him. Anyway, I was able to save these -090 WUR's from the dumpster. PM me or give me a call. What resistance are you getting now?

Tony

[patkeefe]

Hey Tony!
I gave you the only copy of the calcs. What did we determine...the resistances are in as I said in post #11? So, if you get a bad element in one or the other, you will get a non-10-ish ohm reading?

I haven't done much work on the car this summer...had to fix the water cooled section of the fleet, and play golf, of course. I will be examining the SC WUR soon, so I'll post anything I find. I'm pretty sure the two resistance WUR's are for enhanced warm-up control.
Pat

[RarlyL8]

Pat - you are correct, the -090 WUR has 2 strips and the reason is for additional warm-up control. Specifically it is for sever cold weather (below zero) to allow the fuel pressure to raise at a slower rate. More importantly, with this WUR polarity is critical. Switch it and you fry the unit.
No I didn't figure this out by myself, I don't have that kind of time. The info came from Bosch.

[timmy2]

Originally Posted by timmy2

Doesn't matter to a resistor.
Neither side is grounded.

I now know differently due to 090 WUR, it does matter, as I found out about 7 years ago...