The right WUR?

[RDM]

If I am understanding Jim's CIS primer (CIS Primer for the Porsche 911) correctly, the WUR for 1980 was 0 438 140 072. I have 0 438 140 011 marked on mine, which appears nowhere on his table. What do I have installed? And how different is it from what I should have?

[Bob Kontak]

072 may be for US cars with oxygen sensors.

[Walter_Middie]

My Bosch book shows for 1980 911SC:
0 438 140 072
Or
0 438 140 090

Your 0 438 140 011 is listed as Porsche 924 1976-1982. Also used by Volkswagen and Audi.

[RDM]

Originally Posted by Bob Kontak

072 may be for US cars with oxygen sensors.

Bob,

Mine is a US model.

Perhaps this is the cause of my rough running, as the WUR and the Lambda system fight it out for supremacy over the fuel pressure.

[Bobboloo]

Try unhooking the O2 sensor and put a pressure gauge inline to read control pressure to see if the WUR will perform within spec. If it's close enough for warm and cold running then hook the O2 back up and the Lamda will fine tune the system.

P.S. Lamda cars don't use vacuum lines to the WUR. i.e. the vacuum lines on the WUR you have should be unhooked.

[Bob Kontak]

Originally Posted by Bobboloo

Try unhooking the O2 sensor and put a pressure gauge inline to read control pressure to see if the WUR will perform within spec. If it's close enough for warm and cold running then hook the O2 back up and the Lamda will fine tune the system.

P.S. Lamda cars don't use vacuum lines to the WUR. i.e. the vacuum lines on the WUR you have should be unhooked.

Good info.

The frequency valve/Lambda system takes what pressure the WUR gives it and works with that given the output of the oxygen sensor.

The WUR pressure range can be adjusted also if you find the warm pressure specs are out of spec. Need the gauge though and some fiddling is required.

How does the car seem to run?

[boyt911sc]

Originally Posted by RDM

If I am understanding Jim's CIS primer (CIS Primer for the Porsche 911) correctly, the WUR for 1980 was 0 438 140 072. I have 0 438 140 011 marked on mine, which appears nowhere on his table. What do I have installed? And how different is it from what I should have?

Dru,

If you could make the WUR-011 work on your '80 SC would be a good achievement. I'm totally surprise why someone would even install a totally different WUR than the WUR-072. These two (2) WUR's (-011 and -072) are totally different from each other in many ways. They don't even look alike (physical appearance) and totally different configuration. The heating resistances (Ohms) between these two are different.

The -011 could successfully make your engine to run and start from cold but what happens after the engine starts to warm up? What problems are you having now with your engine's performance?

First of all, you need to know your fuel pressures (system and control) both cold and warm states. A set of fuel pressure gauge could identify if the WUR is the culprit or not.

I could loan you one on my WUR-072's to try and test on your car. But you have to decide soon because I'll be going away on vacation (4 weeks) to Carmel, CA for my annual trip to the West Coast and 4 days to go. BTW, the OXS has nothing to do with the operation (directly or directly) of the WUR based from my observation and tests.

Keep us posted.

Tony

[RDM]

Originally Posted by Bob Kontak

Good info.

The frequency valve/Lambda system takes what pressure the WUR gives it and works with that given the output of the oxygen sensor.

The WUR pressure range can be adjusted also if you find the warm pressure specs are out of spec. Need the gauge though and some fiddling is required.

How does the car seem to run?

It runs like a house divided against itself. It revs, then stumbles. It runs like it's missing on one or more cylinders, which gets worse when load increases (as in going up a hill) It gets 15 miles to the gallon on average. It started at a consistent 13 when I got the car ast fall, and I've gotten as high as 17.

Originally Posted by boyt911sc

Dru,

If you could make the WUR-011 work on your '80 SC would be a good achievement. I'm totally surprise why someone would even install a totally different WUR than the WUR-072. These two (2) WUR's (-011 and -072) are totally different from each other in many ways. They don't even look alike (physical appearance) and totally different configuration. The heating resistances (Ohms) between these two are different.

The -011 could successfully make your engine to run and start from cold but what happens after the engine starts to warm up? What problems are you having now with your engine's performance?

First of all, you need to know your fuel pressures (system and control) both cold and warm states. A set of fuel pressure gauge could identify if the WUR is the culprit or not.

I could loan you one on my WUR-072's to try and test on your car. But you have to decide soon because I'll be going away on vacation (4 weeks) to Carmel, CA for my annual trip to the West Coast and 4 days to go. BTW, the OXS has nothing to do with the operation (directly or directly) of the WUR based from my observation and tests.

Keep us posted.

Tony

Tony,

Your trip sounds great!

The car does start pretty well (usually two tries) and runs smoothly while in warmup. But once the Lambda comes on line, it's trying to adjust the A/F ratio. Given the mileage it's getting, I would guess it's cutting off the fuel just when I ask for more.

Please explain the OXS / WUR relationship. I thought the OXS cycled the OXS relay, activating/deactivating the frequency valve, thereby adjusting the fuel pressure.

Oh, and you have a PM!

[Bob Kontak]

Originally Posted by RDM

I thought the OXS cycled the OXS relay, activating/deactivating the frequency valve, thereby adjusting the fuel pressure.

OXS relay provides power to the freq valve. The box the relay is attached to does the thinking and adjusting FP through the freq valve.

If you get a moment, idle your car and rev it up a little. Note the sound. Go pull the OXY relay off and see if the car runs differently (poorly). If no change, that's a big issue. Easy check.

[tirwin]

Maybe I'm wrong but I don't think the FV changes the pressure. The ECU controls how long the FV is open. A 50% duty cycle means it is open half the time. So what it's really controlling is the volume of fuel. The WUR and the FD control pressure.

[Bob Kontak]

Originally Posted by tirwin

Maybe I'm wrong but I don't think the FV changes the pressure. The ECU controls how long the FV is open. A 50% duty cycle means it is open half the time. So what it's really controlling is the volume of fuel. The WUR and the FD control pressure.

I'll buy that but I was pretty darned close. Thanks!! You da Man.

From the CIS primer.

This component is used only on the engines with Lambda control. The duty cycle of pulses sent to the device by the Lambda control box varies the pressure in the lower chambers of the fuel distributor, which controls the fuel mixture.

[tirwin]

Bob,

I don't know... Short of talking to an old fart from Stuttgart, I'm not always entirely sure. I'm still learning. My thinking was that as duty cycle increases towards 100%, that is adding more fuel so the mixture gets richer. The FV valve is just an on/off switch and the ECU tells it how often to open and close. My simple analogy was to think of a beer keg. You pump the tap to build pressure. That's the WUR and the FD. The FV is the spout. And the ECU is me deciding to pour a big beer in my red solo cup so I decide how long the spout is open. And I guess to continue the analogy the O2 sensor is my friend that's telling me to slow down the pour because I'm committing a party foul by making too much foam.

[RDM]

Whatever the answer to whether the pressure changes or not, the ultimate effect is that the wrong WUR, working with (or against) the Lambda system, would produce bad running, right?

Originally Posted by tirwin

Bob,
My thinking was that as duty cycle increases towards 100%, that is adding more fuel so the mixture gets richer. The FV valve is just an on/off switch and the ECU tells it how often to open and close. My simple analogy was to think of a beer keg. You pump the tap to build pressure. That's the WUR and the FD. The FV is the spout. And the ECU is me deciding to pour a big beer in my red solo cup so I decide how long the spout is open. And I guess to continue the analogy the O2 sensor is my friend that's telling me to slow down the pour because I'm committing a party foul by making too much foam.

But what does the FV switch turn on and off? The injectors run all the time (as long as they have more than their opening pressure), so not them. The one frequency valve works on all six injector outputs. So it has to act either before or inside the fuel distributor, right?

Originally Posted by Bob Kontak

I'll buy that but I was pretty darned close. Thanks!! You da Man.

From the CIS primer.

This component is used only on the engines with Lambda control. The duty cycle of pulses sent to the device by the Lambda control box varies the pressure in the lower chambers of the fuel distributor, which controls the fuel mixture.

I think this is more correct. Let me research.

[Bob Kontak]

Originally Posted by RDM

I think this is more correct. Let me research.

FV works before the fuel distributor but is connected to it - changing pressure in one chamber in the the FD - to allow the FD plunger to move more or less delivering more or less fuel.

I do believe your comment about the two systems wrestling against each other is correct now that I read the CIS Primer's description of the FV operation.

The plunger movement in the FD is the key. Two chambers upper and lower. Different pressure in each make the plunger move less or more with a given amount of air flowing past the air sensor.

All of that said, you are correct - a WUR that does not have the same spec as the correct one will deliver a different pressure to one of the chambers in the FD allowing the plunger to move differently than the proper design specs. Therefore more or less fuel running through the injectors than needed.

[tirwin]

Quoting the Probst book:

"When the lambda valve's [frequency valve] duty cycle increases so that it is open longer and returning more fuel to the tank, lower chamber pressure is reduced. The differential pressure valve diaphragms deflect further, reducing upper chamber pressure. This increases the pressure drop at each metering slit and more fuel flows through the slits for any given plunger lift. In short the greater the duty cycle the richer the mixture.

On the other hand, reduced duty cycle means less fuel bleeds off from the lower chamber; that increases chamber pressure and decreases deflection of the diaphragm. This reduces the pressure drop in fuel flow at the slits. So less duty cycle means a leaner mixture."

So I think we were all right. The lambda valve DIRECTLY only opens or closes - changing the volume of fuel. That's what I remember reading and why I was confused by the statement Bob made that it changes the pressure.

It is the volume of fuel going into the lower chamber of the FD that changes the pressure to create a richer or leaner mixture. That was the part I was missing.

[Bob Kontak]

Originally Posted by tirwin

Quoting the Probst book:"When the lambda valve's [frequency valve] duty cycle increases so that it is open longer and returning more fuel to the tank, lower chamber pressure is reduced.

Excellent info. I did not know how the freq valve actually changes the pressure. Probst's book is great.

[RDM]

Sagt Probst:



The picture is much easier to understand than the description, which is more detailed.

"[T]he amount of time the valve is open controls the pressure in the lower chambers of the differential pressure valves. This in turn changes the upper-chamber pressure to change the pressure drop and change enrichment.

"The opening of the lambda valve is controlled b the electronic control unit which monitors the signal from the lambda sensor (also known as the oxygen sensor). The lambda sensor sends a signal to the control unit which is based on the oxygen content in the exhaust. The control unit then operates the lambda valve to control lower-chamber pressure."

...

"When the lambda valves duty cycle increases so that it is open longer and returning more fuel to the tank, lower-chamber pressure is reduced. The differential-pressure valves deflect further, reducing upper-chamber pressure. This increases the pressure drop at each metering slit and more fuel flows through the slits for a given plunger lift. In short, the greater the duty cycle, the richer the mixture."

Probst, pp 5-22-23

So at 13 MPG, the lambda sensor reads rich, reduces the duty cycle, thus reducing the amount of fuel delivered, causing the car to stumble.

< I see I'm too slow with this info. Thanks, guys!>

[Bob Kontak]

Originally Posted by RDM

< I see I'm too slow with this info. Thanks, guys!>

Just a simple overlap. We are all on the same page and you were the first one on that page.

Probst's info is great. For the life of me I pictured the "slits" in the plunger and when the plunger went up and down, more or less based on the pressure diff in the chambers, it would meter more or less fuel.

Your reference indicates the plunger/sensor plate movement is independent of chamber pressure. I ain't gonna argue with Charles P, so I just need to do some refresh reading. Been a while.

These kind of threads are way more fun than the AC ones. :-)

All the best.

[RDM]

Originally Posted by Bob Kontak

Your reference indicates the plunger/sensor plate movement is independent of chamber pressure. I ain't gonna argue with Charles P, so I just need to do some refresh reading. Been a while.

These kind of threads are way more fun than the AC ones. :-)

All the best.

More plunger movement = more upper chamber pressure = more fuel flow

AC? That's on my shelf. Got in the way of looking for vacuum leaks!

[tirwin]

Originally Posted by Bob Kontak

These kind of threads are way more fun than the AC ones. :-)

All the best.

Amen!