033 WUR Spec Question

[jma0506]

I am trying to wrap my head around the specs of the 033 WUR compared to the readings I am getting on my recently refurbished 033 WUR for my '77 911S 2.7.

I have run all the various pressure tests to baseline the measurements of the rebuilt WUR before starting up the car. Everything I have come across in the workshop manual and in this forum tells me that my CCP numbers are lower than they should be.


My Pressure Readings:

1977 911S 2.7 - 033 WUR
System Pressure: 4.9 Bar
CCP (no Vac) @ 17C: 0.9 Bar [LOW]
CCP (with Vac) @ 17C: 1.5 Bar [LOW]
WCP (no Vac): 2.7 Bar
WCP (with Vac): 3.6 Bar

The additional point of confusion I have is what the source of truth for the 033 CCP is - there seems to be two different CCP charts [see below].

Robert Bosch


Workshop Manual


There are 2 differences between these two charts: the ~0.5 Bar difference in each scale and the workshop manual seems to imply CCP is measured with vacuum.




So based on all of this, I am hoping to answer the following questions:

1) Is the inherent difference between the Robert Bosch Graph and the 911 Workshop manual simply excluding vacuum (bosch) and including vacuum (workshop) in the CCP measurement? The delta between the two looks to be ~0.5 Bar on average which is the delta I measured between my CCP with and without vacuum.

2) Which chart is the source of truth for 033? And if it is the workshop manual, should we be testing CCP with vacuum applied or not?

3) With my WUR CCP numbers being low, in order to increase the CCP of the 033 do I need to raise or lower the pin located between the top vac port and electrical connector? I am thinking raise based on the below image.

[Classic 911]

Following


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[hughc]

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[boyt911sc]

Josh,

If you are NOT happy and satisfied with your newly rebuilt WUR-033, contact the rebuilder and explain your out of spec control pressure values. You should not be fixing it in the first place and lose the warranty. If the rebuilder does not do to correct the problem or refused to help, you have a responsibility to this community to prevent other members from getting into similar situation by mentioning the identify of your rebuilder. Simply bringing up a customer dissatisfaction to the attention of the other party should be enough to resolve your problem. Good luck.

Tony

[jma0506]

Thanks Tony. I am in the process of resolving this with the rebuilder and am also trying to educate myself in the process as well. I am consulting the forum to try and get to an understanding of what CCP I should be expecting at 17*C and whether that is being measured with our without vacuum as per the above charts above. I appreciate any help or guidance on this point specifically, thanks!

[jma0506]

For those following, after speaking with Kurt from Klassikats he helped clarify an answer to question #2:

Which chart is the source of truth for 033? And if it is the workshop manual, should we be testing CCP with vacuum applied or not?

He (and Tony) both go by the Workshop Manual chart. The recommendation is to measure cold control pressure without vacuum. Why? The reason is because there is no vacuum at cranking speed and the 1977 911s has a thermo vacuum valve that counteracts the direct vacuum signal to the top of the diaphragm of the 033 WUR. Vacuum doesn't get applied to the WUR until the thermo vacuum valve opens after ~20-30 seconds.

Hopefully this helps clarify the CCP measurement approach for 1977 911s owners with a 033 WUR.


So the million dollar question: Why does the workshop manual say apply vacuum when measuring CCP? I have my own theory that I'd love to have validated or debunked.

The CIS Specifications page of the workshop manual covers the 1976 and 1977 911S. Both cars came with the 033 WUR but it wasn't until 1977 that the thermo valve was added to the car (along with '78 and '79).

For those of us who have tried to understand the vacuum line connections on a '76 or '77 (i have certainly come across a number of conflicting drawings), there is a clear difference in how the lines are connected between these 2 years. In 1976, the WUR vacuum port is connected to a T that comes off of the deceleration valve on the back side of the throttle body. In 1977, the deceleration valve is isolated to the back of the throttle body and a T is instead connected between the distributor vac line, bottom front port of throttle body and the WUR vacuum port by way of the thermo valve.

So based on this could we say that because the '76 does not have the thermo valve and has vacuum connected to the WUR from the decel valve that it would expect vacuum at the WUR just after a cold start where as the '77 has the thermo valve blocking vacuum to the WUR for ~30s after cold start? And if so a '76 should have it's CCP measured with vacuum but a '77 should have it's CCP measured without vacuum? And if we agree with that theory then the workshop manual CCP measurement approach is written for the 1976 and was not updated to reflect the changes made to the 1977?

Well if you've made it this far let me know what you think!

[icarp]

I can start my CIS engine with out any WUR at all.
I made a simple hand adjustable pressure regulator , I set the pressure to a reasonable pressure and it starts right up.
This system is very basic , 5-10-15psi off of exact, usually starts the engine .
I do not know anyone that knows more about the CIS systems than Tony.
I recommend you pic your team and stick with it , end of story.
It is your choice .

Ian

[Bimmers4Life]

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[jma0506]

Thanks icarp, not trying to pick teams here but appreciate the response.

I'm more focused on a thoughtful discussion around the nuances of what the workshop manual says about measuring CCP for a 033 WUR, theories around the perceived discrepancy and letting those who have worked on the 033 WUR chime in on their approach to measuring CCP either with or without vacuum and why as well as the expected values of CCP with or without vacuum at say 18*C.

[boyt911sc]

Josh,

What is the status of your newly rebuilt WUR-033? Everything OK now?

Tony

[jma0506]

Hi Tony,

Thanks for checking in. The WUR is back being recalibrated to the following specs that I provided them:

CCP (no Vac) @ 18C: 1.7-2.1 Bar
CCP (with Vac) @ 18C: 2.2-2.6 Bar
WCP (no Vac): 2.7-3.1 Bar
WCP (with Vac): 3.4-3.8 Bar

Let me know if you think these values are inaccurate. I should have it back soon after which I'll install it, rerun the pressure test and provide an update.

Thanks,
Josh

[boyt911sc]

Originally Posted by jma0506

Hi Tony,

Thanks for checking in. The WUR is back being recalibrated to the following specs that I provided them:

CCP (no Vac) @ 18C: 1.7-2.1 Bar
CCP (with Vac) @ 18C: 2.2-2.6 Bar
WCP (no Vac): 2.7-3.1 Bar
WCP (with Vac): 3.4-3.8 Bar

Let me know if you think these values are inaccurate. I should have it back soon after which I'll install it, rerun the pressure test and provide an update.

Thanks,
Josh

Josh,

Those numbers were taken from the PSM (Porsche Shop Manual) data sheet and chart. And I use them for reference. Any value within the range is considered acceptable. But what you will ask later, was the WUR correctly calibrated? Not until you get back the WUR, you won’t know the answer to this question.

Why are you telling your rebuilder how to do their job. You paid a lot of $$$ for their service and expect in return a good working WUR-033. Hope you get this problem sorted soon because summer is just around the corner.

You could have borrowed a WUR-033 since we had met before in one of my earlier Engine Rebuilding Workshops. Wish you luck.

Tony

[PeteKz]

Josh, follow up to your question about which graph is correct. I think you were trying to read too much into it. One chart is with vacuum applied, and other other is without vacuum applied. The print under the chart also gives the differences in CP with and without vacuum, and it's about 0.5 bar (7psi), as you measured. They work out to the same results.

I think it's a simple case of Bosch published the graph one way, and whoever at Porsche wrote the PSM decided to publish it the other way. As the 14th Century philosopher and theologian supposedly said, don't add complexity--the simpler explanation is usually the better one.

[boyt911sc]

Josh,

It would be helpful for others if you share your experience. Were you able to get the WUR corrected? If not, did you get a refund? Would you recommend it to your friends? Thanks.

Tony

[kepa75]

Hello,

I've also a car with a 033 WUR and I have a varition in warm contol pressure of 0.8 - 0.9 bar from with to without vacuum applied. This is more than than it should be and the car runs to lean. So, is there a way to set the vacuum correction to a 0.5 bar difference?

Thanks,
Peter