924Board.org

[Tiny]

+1 to the above.

I also usually place a workshop cloth just under the WUR before you start as you don't wanna drop a bolt or copper washer down a dark chasm.
Its a real pain worth avoiding!
Tiny
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*****1981 - 924 - Auto - London, UK******

[jrcook320]

I've done some testing of control pressures on a boost sensing WUR like this from an audi 5000s and the volvo 240 turbo.

To start off, I drilled a hole in the brass plug over the bottom stop of the diaphragm to access the allen adjusting screw. This allows simple adjustment of warm control pressure via the secondary spring. This also makes it so you can't plumb the vacuum lines they way they would be stock on a volvo, which is better anyway. It should be plumbed like on the 930 & 964, with a single boost line above the diaphragm. This also allowed me to watch diaphragm movement.

By applying pressure to the top port, the diaphragm moved downward, lowering control pressure by about 20 lbs on my system. Applying vacuum to the upper port made no movement of the diaphragm and no change in CP, which means that the diaphragm is all the way up at 0 manifold pressure and negative manifold pressure. This means there is no vacuum enleanment (if that's a word).
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| '81 320i Turbo | T25, 931 CIS, 250hp, 13.92@100mph | e21 Legion Page | My E21 Videos |

[Smoothie]

Very interesting - so I might have to go back to my original theory on how it works and un-yellow the "yellowed-out nonsense" in my first post..
-But this would mean the load enrichment WUR is useless as an upgrade for an NA.
Are you sure this is correct?.. That negative to zero pressure = no affect on control pressure, and > zero pressure (positive pressure) = gradual lowering of control pressure..?
More interested in getting the facts straight than "being right", so if these are the facts, obviously my earlier comments need to be reversed again..

[jrcook320]

I am sorry, I am not sure this is correct.

I can only vouch for what I have tested on 2 turbo WUR's, which unfortunately did not show decreased control pressure under vacuum. This would benefit a turbo car as much as an NA car to increase throttle response.

I actually just downloaded a bosch manual that says otherwise, that the mixture is leaned out under vacuum which means there is upward travel available. It did not discuss boost conditions, however.

The difference must be in where the diaphragm travel stops are positioned. There may be a pretension of the diaphragm as well...
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| '81 320i Turbo | T25, 931 CIS, 250hp, 13.92@100mph | e21 Legion Page | My E21 Videos |

[Rasta Monsta]

I am surely missing something, but why would you want to richen the mixture under vaccuum?
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[jrcook320]

You don't. The vacuum is applied above the diaphram, which increases control pressure, thus leaning the mixture.

Ideally, at throttle tip in, vacuum lowers and control pressure drops to give good throttle response, and even reduce lag on a turbo setup. Then under boost teh diaphram drops further to give max wot enrichment.
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| '81 320i Turbo | T25, 931 CIS, 250hp, 13.92@100mph | e21 Legion Page | My E21 Videos |

[Smoothie]

I just did a Yahoo search on cis wur vacuum. Not too suprisingly WURs were apparently made with an assortment of different functionalities.. -From the simplest temperature operated one without vacuum or boost hookup, to the temperature and vacuum operated type that's in enrichment mode at 0"Hg and gets "pulled" into a leaner state under vacuum, ..to a temp, vacuum, and boost operated version that's also "pulled" into a leaner state under vacuum, goes richer as vacuum decreases up to 0"Hg, then enriches further under boost.

I'm pretty sure that lambda (o2 sensor) equipped 931s like mine got the second type that's affected only by temperature and vacuum. -Because at full throttle the lambda system increases the duty cycle of the frequency valve to enrich the mix (it would seem redundant to have both the WUR and the frequency valve enriching the mix at WOT)(Until it's verified by testing a North American 931 WUR this is still just a partially educated guess that this is the type we got with lambda.) Of course the rest of the worlds' 931s that didn't get the lambda system would need a way to enrich under boost, so my guess is that they got the 3rd type of WUR that's all 3 - temperature, vacuum, and boost-operated.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[jrcook320]

Correct. The only real difference between the latter 2 is the travel range of the vacuum diaphragm. This is determined by the position of the lower max travel stop. I am currently wondering if there is also a difference in the "preload" tension of the diaphragm. The diagram posted above is discussing a vacuum WUR, and it shows the diaphragm at the top travel stop under vacuum, and lowering to the bottom travel stop at 0 pressure. In this case, there is nothing pushing the diaphragm down, so I would think the diaphragm's home position is the lower stop, ie, preloaded in that direction. That is unless the home position is somewhere in the middle of the 2 stops and fuel pressure is actually able to push the diaphragm down for enrichment at 0 psi.

If a boost sensing WUR went to full rich at 0 psig, it wouldn't be able to provide any boost enrichment. At 0 psi, it would have to be somewhere in the middle of it's travel range. BUT, from what I have observed, the home position of a turbo WUR's diaphram is at the TOP stop, which means it's preloaded in the opposite direction. This also means that it doesn't provide any change in control pressure until there is positive pressure applied.

I observed this top stop home position on a WUR off the car (with NO fuel pressure) and watched the diaphram move from top stop at 0 psi to the lower stop under pressure. I then tested the WUR on my car, with fuel pump jumpered and observing control pressures while applying pressure, then vacuum. I only noticed a drop in CP under "boost", but CP did not raise under vacuum. I'm going to re-do this second test to be sure I didn't mess it up or miss anything, and I will get back with you guys on it. It seems like there should also be vacuum adjustment range, so I'm HOPING I screwed the test up and that fuel pressure is enough to push the diaphram away from the top stop enough to allow for some vacuum enleanment.

Consider a vacuum WUR like a performance "chip" for an obd1 car. It can provide better fuel mileage, better throttle response, and more power under WOT due to the richer mixture a motor needs.

As for depending on the frequency valve for boost enrichment on US 931's, that is fine if the "ecu" is actually capable of hitting the proper AFR with the frequency valve. What AFR does the ECU hit? if it's higher than 12.0:1, then I would argue that it is not adequate for boost enrichment by itself. In my case, with my current tune (which is soon to change), the stock e21 ECU can't hit 12.0 AFR with a boost sensing wur helping it.
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| '81 320i Turbo | T25, 931 CIS, 250hp, 13.92@100mph | e21 Legion Page | My E21 Videos |

[jrcook320]

So, last night I did my test again and recorded my findings. It is very odd, but with it plumbed volvo style, I get immediate drop in CP (which means better throttle response & less turbo lag). I tried to drive to work today with just one line to the top port. The car would idle fine but I couldn't accelerate so I had to switch it back. I need to just take my spare audi 5000s WUR appart and see if my theory of diaphragm preload is correct and see if I can adjust the "top" stop enough to give me vacuum travel or not (If there is preload, I doubt it as the top stop is the body of the WUR). I know that there is a 928 company that modifies a vacuum WUR to also have boost range by moving the lower stop.

Here are my findings:
1 Vacuum/boost line to top port of WUR (similar to the 911)
WCP @ 0" Hg = 54 psi (fuel pump jumpered)
WCP @ idle, 19" Hg = 56 psi
Throttle blip to 5" Hg = no change, 56 psi
AFR @ idle, closed loop = 13.2 - 13.4

Vacuum/boost line to top port, vacuum line w/ delay valve on bottom port (volvo plumbing):
WCP @ 0" Hg = 54 psi (fuel pump jumpered)
WcP @ idle, 19" hg = 47 psi
Throttle blip to 5" Hg = CP dropped to 30 psi
AFR @ idle, closed loop = 12.6 - 12.8

In the second test, what I think is happening is the diaphragm is pulled down some by equal vacuum on both ports. Once vacuum drops (throttle tip in), the delay valve (much like a check valve to keep boost from reaching the lower port) holds vacuum under the diaphragm while pressure rises above the diaphragm, allowing the diaphram to drop to give instant drop in control pressure and excellent throttle response. This works much like an accelerator pump on a carb would. Under boost, the top port sees full boost pressure, the lower port sees nothing.

Remember, these findings are for the Volvo 240 turbo WUR. If you're running a vacuum sensing WUR (with 1 vac nipple above the diaphragm), you can probably modify it to sense both vacuum and boost with only 1 vacuum line attached by pulling the lower stop out.
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| '81 320i Turbo | T25, 931 CIS, 250hp, 13.92@100mph | e21 Legion Page | My E21 Videos |

[jrcook320]

so, I've learned quite a bit from the time I first posted on this thread. I took apart my audi 5000s WUR and it does have a coil spring on the bottom side of the diaphragm which preloads the diaphragm at the top stop. This type of WUR has 2 ports, one above and one below the diaphragm, and the lower port has to have a check valve to keep positive pressure from entering the lower chamber. As my testing confirms, on throttle tip in, pressure in the upper chamber rises while the check valve holds vacuum in the lower chamber. This pulls the diaphragm down to lower control pressure. Also, 0" vacuum and boost conditions don't really produce different control pressures so this style is technically just a more complicated vacuum sensing WUR. With the volvo FD and AFM installed and the lambda system working, it is enough to get WOT afr to 11.9:1, which really is ideal (safety wise) for a turbo application.

Smoothie, I think your original theory about a vacuum sensing diaphragm must be correct. That type of WUR must be preloaded on the bottom stop so that vacuum pulls the diaphragm up, while 0" lets it drop back to the lower position. The only way to be sure is to take one apart and see. Can anyone verify what type the 931 used? How is the 931 WUR plumbed? This will be a big indication as to how it functions internally.

I am wondering what it would do to have a spring above and below the diaphragm so that the 0" hg rest position is in the middle of travel. Then all you would need is a single line above the diaphragm to pull the diaphragm up under vacuum and push it down under boost.
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| '81 320i Turbo | T25, 931 CIS, 250hp, 13.92@100mph | e21 Legion Page | My E21 Videos |

[Fasteddie313]

I would also like to know how a 931 WUR is supposed to be plumbed..

My car has post TB vac to item 9 in the WUR diagram and nothing but a vent to item 3.. I want to make sure my connections are correct..

It seems counterintuitive that connection 9 should be used vs item 3..


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80 Turbo - Slightly Modified

[Johann]

Interesting topic. I am learning so much from you guys!!

My car(ROW '83 931 with DITC), and a friends car (ROW '82 931 with DITC) has a vacuum tube going into port 9 coming from a vacuum port on the charge pipe before the throttle body.

Looking at the diagram in this topic It states that you need to hook the vacuum line up to port 3 with Port 9 acting as a vent. However, if you want diaphragm 10 to go down, pulling the plunger down and as a result diaphragm 4 down making rhe car run richer you will need high pressure inside the bigger chamber and low pressure in the small chamber.

So, that means hooking vacuum up to port 9 is correct and the diagram has it wrong?

[Carrera RSR]

[Johann]

Thanks Carrera RSR.