How to test functionality of 089 WUR VACUUM diaphragm?

[Mtsurfposse]

How do you test the functionality of a the WUR vacuum assisted diaphragm? The end result is vacuum is held when THROTTLE is applied resulting in a lean condition at med to heavy throttle.
I’ve tested two ways, while driving shutting off manifold vacuum to WUR. Vacuum is held for indefinite period
Statically I’ve applied vacuum to lower nipple and vacuum will be held for over 1 minute.
I’ve tried with vacuum and without vacuum to pull and blow low pressure air through relief valve that is connected from the top of the WUR to the upper throttle body nipples

Also, if the diaphragms relief is blocked any tips for clearing a clog in place or is removal a disassemble the only answer. Also pictures of what allows the relief between the lower and upper chambers would be great as I’m not sure how the equilibrium is established when throttle is applied… one hole in the diaphragm, many? Some other port or valve?

[PeteKz]

The tech specs book has the values for testing the control pressure of the WUR. There also is a spec for applying a certain vacuum (450-550 mbar) and how much that should change the CP. Your tests show the internal diaphragms are good. If it provides the correct CP from cold to warm, and applying the specified vacuum changes the CP the specified amount, it's working as designed.

BTW, the 089 is more complicated internally than the others and has two diaphragms, IIRC. It's no big deal to open it up and inspect internally. Just don't pull on the diaphragms and possibly damage them.

[Mtsurfposse]

But it’s not working as it should. There not the reduction in manifold pressure under WOT that should reduce control pressure and it’s not.
The Porsche designers attached the top hose to atmospheric for a reason. That reason should have been for make up air for the lower chamber when pressure is reduced. If it was supposed to be an air tight chamber they never would have put that nipple on the top.

Makeup air passing through the upper nipple to the lower chamber should allow for the rapid removal of vacuum pressure that causes lean fuel.

Many if not most vacuum systems are not air tight but rely on small leaks to work or overcome small leaks with CFM. Small leak, big CFM no problem to hold vacuum. That’s usually how the systems are worked out as it’s much cheaper than other regulators. The control pressure fuel system in our cars works the same way by squeezing a set system pressure of fuel through a modulated hole size increasing or decreasing our fuel pressure

[Mtsurfposse]

So I found something… Skynet(ChatGPT) found a few pages for me

It uses the language “air bleed channel” to describe upper to lower connection and describes procedure to test as applying 10”hg to lower port and counting

If it briefly, the air channel is fine. If it holds indefinitely, it is fouled for some reason…

In the same generic Bosch K manual it also describes how the vacuum is related to only inner spring and during idle at max vacuum it’s at its max preset tension

So I guess I tear into it? Try to unclog this air bleed channel and try to not muck with anything else or have you or anyone else opinions on proper range between control pressure with vacuum and without vacuum
IE what’s the preferred variance between control pressures?

[PeteKz]

Yes, the top nipple allows for atmospheric pressure on one side of the diaphragm. Vacuum is applied to the other side.

Did you test the WUR CP with 450-550 mbar applied? Did you apply it directly to the WUR vacuum nipple (not through the TV)? With vacuum applied, the CP should increase (leaner), without vacuum it should drop down (richer). What happened?

Open up your WUR and look at the internals. That will help you understand it.

[Mtsurfposse]

So the test described is to test whether a change occurs when manifold vacuum pressure decreases. That test is apply 10 inches of mercury to the lower port and see how long it hold that vacuum. The engine doesn’t have to be running for this test and the upper port could be connected or even better disconnected and it should hold vacuum briefly and then lose pressure rather quickly if it does not hold vacuum at all, then your diaphragm is ruptured if it holds vacuum indefinitely then there’s a clog in the air bleed, which connects the upper port to the lower port and relieves the vacuum pressure when you step on the gas

And yes,with with vacuum, my warm control pressure is 3.8 without it is 2.8. However, once vacuum is applied the word holds that vacuum until the car is shut off or the hose is pulled off.

When opening up the WUR Have you had your eyes on the air bleed before? Does the WUR try and blow itself into 1 billion bits because of the springs when you open it up or does it stay contained held in place by screws and bolts

[boyt911sc]

Mt,

You are over thinking this simple device. Tear it apart to satisfy your curiosity. Don’t worry if you mess it up. I will re-calibrate it for you for FREE. BTW, are you using a hand held vacuum pump like a Mity Vac? How do you test the fuel pressure? With the motor running or just the FP running? Keep us posted. Thanks.

Tony

[Mtsurfposse]

Thanks for the offer Tony, hopefully I won’t have to take you up on it but totally will if the shisse hits the fan

I take it you don’t test or worry about the air bleed channel. Have you never found them clogged before?

I’ve tested running and just using a jumper, results are the same. I use multiple vacuum set ups depending on need, sometimes a pump, sometimes handheld.

If you think I’m overthinking the WUR what else would cause the lack of control pressure drop in response to WOT. The internal spring and diaphragm appear to act properly as there is an immediate change when vacuum is applied or pulled by attaching or removing the vacuum hose.

[Mtsurfposse]

Here are the two vacuum layouts I’ve tried

[PeteKz]

It's hard to tell from the 2nd diagram where the blue and red hoses go on the throttle body. With the 089 WUR, the red line should go to the atmospheric vent, which is the top rear (back of the car) nipple on the TB; NOT to the TV . Other WURS have different routing.

At any rate, the first diagram is what you should use. NOTE: I elected to go from the vacuum nipple on my 089 WUR to the lower airbox fitting (which is for power brakes on SC models). I think it works better that way. At least my AFR gauge acts more like I expect it to act.

It's been 2 years since I had my 089 WUR apart, so my memory might be off, but I do not recall any air channels that would allow the vacuum in the WUR to bleed down. If you pull a vacuum on that nipple, it should hold that vacuum. Maybe Tony has better info.

[Mtsurfposse]

You’re right the second diagram wasn’t clear, so I erased it. The functionality of that older WUR is reversed so the picture looks wrong

As you suggest, if you pulled vacuum on the top port of our 089 it would pull the diaphragm up and seal the lower chamber, but If you blew air in it would flow out through the lower nipple.
Anyway. I’ve got to crack things open and I’ll report back, with what I hope is the proper solution to our improper enrichment

[Mtsurfposse]

Ps here’s a pic showing a cut away of a WUR with the air bleed channel just above the diaphragm. It’s still not clear to me where this opens to the upper chamber or what I’ll need to do once in there but I’ll soon find out

[boyt911sc]

Originally Posted by Mtsurfposse

You’re right the second diagram wasn’t clear, so I erased it. The functionality of that older WUR is reversed so the picture looks wrong

As you suggest, if you pulled vacuum on the top port of our 089 it would pull the diaphragm up and seal the lower chamber, but If you blew air in it would flow out through the lower nipple.
Anyway. I’ve got to crack things open and I’ll report back, with what I hope is the proper solution to our improper enrichment

Mt,

If you blow air to the top port, the air will NOT go through the lower nipple unless you have a defective diaphragm. Since you were able to create vacuum using the top port, you have demonstrated that the diaphragm is good and not leaking.

Your understanding about how the WUR-089 is constructed is flawed. Repeat your test. I bet your result will be different.

Tony

[boyt911sc]

Originally Posted by Mtsurfposse

So the test described is to test whether a change occurs when manifold vacuum pressure decreases. That test is apply 10 inches of mercury to the lower port and see how long it hold that vacuum. The engine doesn’t have to be running for this test and the upper port could be connected or even better disconnected and it should hold vacuum briefly and then lose pressure rather quickly if it does not hold vacuum at all, then your diaphragm is ruptured if it holds vacuum indefinitely then there’s a clog in the air bleed, which connects the upper port to the lower port and relieves the vacuum pressure when you step on the gas

And yes,with with vacuum, my warm control pressure is 3.8 without it is 2.8. However, once vacuum is applied the word holds that vacuum until the car is shut off or the hose is pulled off.

When opening up the WUR Have you had your eyes on the air bleed before? Does the WUR try and blow itself into 1 billion bits because of the springs when you open it up or does it stay contained held in place by screws and bolts

Scott,

Now that you had a chance to disassemble a good working WUR-089, did you figure out where the air valve is located? Keep us posted. Thanks.

Tony