Odd WUR connections

[Cornerlot]

My '76 911S came fitted with an incorrect WUR which seems to be working (I installed a rebuild kit from Salvox), but I'm not sure of the vacuum connections. Its a 0438140034 (same as pictured) 'double diaphragm' style intended for various Ferrari, Audi, and Renault applications. But, is the top vacuum nipple intended to be the vent or the manifold source vacuum? I under stand that the pre-78 Porsche units with bottom nipples had the source vacuum there, and was switched in '78 to vacuum a the top. Which way should I connect this beast?

Steve

[fanaudical]

My understanding is that the top port is "manifold source vacuum" and the bottom port is "reference" or "vent".

[Cornerlot]

Originally Posted by Cornerlot

My '76 911S came fitted with an incorrect WUR which seems to be working (I installed a rebuild kit from Salvox)...]

Well, 'seems to be working' but not correctly. The warm control pressure is a tad low at 2.9 bar, but cold its only 0.85 bar. I'll reset the pin and see if I can get the cold up to 2.0 bar or so. I'm not sure if this WUR will have a pressure curve that will be correct from that point, stopping at just over 3 bar when warm.

Steve

[boyt911sc]

Originally Posted by Cornerlot

My '76 911S came fitted with an incorrect WUR which seems to be working (I installed a rebuild kit from Salvox), but I'm not sure of the vacuum connections. Its a 0438140034 (same as pictured) 'double diaphragm' style intended for various Ferrari, Audi, and Renault applications. But, is the top vacuum nipple intended to be the vent or the manifold source vacuum? I under stand that the pre-78 Porsche units with bottom nipples had the source vacuum there, and was switched in '78 to vacuum a the top. Which way should I connect this beast?

Steve

Steve,

Check with the WUR rebuilder how this particular warm up regulator is connected. You will get different answers from this forum because this WUR is not used in 911 applications. I doubt this would work well with '76S because it is totally different from a WUR-033. However, if you could make it work like a WUR-033 use it. Good luck.

Tony

[Cornerlot]

I was able to reset the cold and warm control pressures spot on, which is great. I'm not sure of the vacuum yet. Applying vacuum to the top port reduces the control pressure (richer to injectors), but which throttle body port will increase vacuum (ideally change from ambient to a vacuum state) under load? Vacuum to the bottom port did nothing.

Steve

[Cornerlot]

Originally Posted by Cornerlot

I was able to reset the cold and warm control pressures spot on, which is great. I'm not sure of the vacuum yet. Applying vacuum to the top port reduces the control pressure (richer to injectors), but which throttle body port will increase vacuum (ideally change from ambient to a vacuum state) under load? Vacuum to the bottom port did nothing.

Steve

I've re-read the Bosch CIS manual, and it looks like the WUR upper chamber should see POSITIVE pressure (or at least greater than the bottom chamber) from below the throttle (their words) to decrease the control pressure. Now, it shouldn't reduce the control pressure with vacuum to the upper chamber (diaphragm is against the stop already), but in my test it did do that. Strange, maybe this WUR works different than the text book example.

The theory is confusing in that you would never expect to see positive pressure in the manifold of an aspirated engine (maybe some ram manifolds near closed valves).

I'm missing some piece of data, somewhere.

[boyt911sc]

Originally Posted by Cornerlot

I've re-read the Bosch CIS manual, and it looks like the WUR upper chamber should see POSITIVE pressure (or at least greater than the bottom chamber) from below the throttle (their words) to decrease the control pressure. Now, it shouldn't reduce the control pressure with vacuum to the upper chamber (diaphragm is against the stop already), but in my test it did do that. Strange, maybe this WUR works different than the text book example.

The theory is confusing in that you would never expect to see positive pressure in the manifold of an aspirated engine (maybe some ram manifolds near closed valves).

I'm missing some piece of data, somewhere.

You have to know and understand how a specific Bosch WUR (0-438-140-xxx) works. They have different characteristics and function. Including the the locations of the vacuum port from the throttle body. A simple way is just use the standard configuration for your model year and using the right component/s. Your WUR-034 may work in your engine if you know how it works. Unfortunately, that is a totally different WUR for your specific engine. Do you have a control fuel chart for WUR-034? Why are you using a WUR-034? Keep us posted.

Tony

[Cornerlot]

Originally Posted by boyt911sc

Why are you using a WUR-034? Keep us posted.

Tony

This is what was on the car when purchased, and using it saves the several hundred dollars it would cost for a replacement. I think it will be OK (the control pressures without vacuum are fine now), its the vacuum/pressure signaled enrichment that has me stumped. I've sent a note to the Ferrari 400 - Home (great CIS resource) site master asking for info on it, so maybe tomorrow I'll hear back (he's in Europe).

Porsche did go to a vacuum based load-enrichment WUR in 1978 I believe, but its bottom port faces 90 degrees rotated to the side, and MAY operate different.

It's the wording in the Bosch tech manual that stumps me, it is not model specific and may describe either the Ferrari or Porsche style, or both. I think if vacuum was supplied to both the top port and bottom ports, but the pressure increased to the top chamber, it may function like the book says. But, my testing with vacuum only to the top chamber shows that would run the CIS richer at idle, not desirable at all!

Steve