089 WUR spec

[Alan L]

What is the flow rate the FD on my SC should be delivering to the WUR?
I have a pump rate of 1500cc/30 sec.
The flow from the top of the FD to the WUR inlet is showing 110cc/30 sec. Which I think is a bit low?
I am getting zero control pressure (after having pulled the WUR apart).
Trying to find source of problem. Suspect the metering diaphragm must be wide open - but changed nothing in terms of the settings. Trying to eliminate all the spec settings. System pressure 4.9 bar.
Alan

[boyt911sc]

Originally Posted by Alan L

What is the flow rate the FD on my SC should be delivering to the WUR?
I have a pump rate of 1500cc/30 sec.
The flow from the top of the FD to the WUR inlet is showing 110cc/30 sec. Which I think is a bit low?
I am getting zero control pressure (after having pulled the WUR apart).
Trying to find source of problem. Suspect the metering diaphragm must be wide open - but changed nothing in terms of the settings. Trying to eliminate all the spec settings. System pressure 4.9 bar.
Alan

Alan,

Check the pin. The “pin” for the “sombrero” has been dislodged and sitting somewhere inside the WUR. Are you sure it was ZERO pressure reading? The presence of a new stainless screen mesh (filter) and stainless diaphragm would give you a reading at least 4~5 psi.

When doing a flow test (pin removed), I always get some pressure readings on the gauge but NEVER ZERO. And I have done thousands of these flow tests over the years.

Tony

[Alan L]

Hi Tony,
Absolutely zero pressure. And I had the WUR apart again to check. Pin is in place. I can get a semblance of normal control pressure if I insert another spring on the bottom of the diaphragm (adding more pressure to the sombrero and pin) - like the 930 WUR has. So it is capable of working.
I have a flow spec for the 930 WUR of around 145 cc/30 sec to the WUR. But my manuals usually do not give the number, or at best wide range of what to look for . Trying to ascertain I have enough fuel flowing in to the WUR.
Regards
Alan

[Alan L]

Just checked 930 specs - around 130cc/30 sec is high end of spec.
So at 110 for the SC, I suspect that is correct.
Problem lies elsewhere
Alan

[Alan L]

Checked and reassembled WUR again, this time got 3-4 psi. Tightened the housing screws down as hard as they go. Maybe that was a difference. But reluctant to shift the finger's plug setting unless have to.
How would the internal settings change so much - unless they are governed by a few thou in reassembly. Maybe.
Would you move the plug Tony, or look for an alternative?
Alan

[boyt911sc]

Originally Posted by Alan L

Hi Tony,
Absolutely zero pressure. And I had the WUR apart again to check. Pin is in place. I can get a semblance of normal control pressure if I insert another spring on the bottom of the diaphragm (adding more pressure to the sombrero and pin) - like the 930 WUR has. So it is capable of working.
I have a flow spec for the 930 WUR of around 145 cc/30 sec to the WUR. But my manuals usually do not give the number, or at best wide range of what to look for . Trying to ascertain I have enough fuel flowing in to the WUR.
Regards
Alan

Alan,

Test and verify your pressure gauge is good and working. Are you sure there is fuel flow between FD and WUR? Yours could be a SUSPECT gauge.



Tony

[Alan L]

The gauge is fine. When I turn the pump off, it shoots up to around 2 bar. Then slowly bleeds off to zero over the next minute or so.
Alan

[boyt911sc]

Originally Posted by Alan L

The gauge is fine. When I turn the pump off, it shoots up to around 2 bar. Then slowly bleeds off to zero over the next minute or so.
Alan

Alan,

If you have “0” pressure reading with the fuel pump running, turning OFF the FP should NOT give you more or higher pressure reading. Highly not feasible.

Tony

[Alan L]

Tony - I can confidently tell you - that is exactly what I am seeing. I have repeated it several times now. Same result. Fuel pump running = zero pressure on CIS gauge. I can let it run as long as you like - it does not change (I have the power to the WUR disconnected). (If I shut the valve I get Sys P.)
I turn the pump off with zero WUR pressure, and go back to the gauge and it sits about where the CP should be, and slowly drops to zero - over 1-2 mins. That is exactly what I am seeing.
Regards
Alan

[Alan L]

I have taken a video of the behaviour - but don't know how to post it. Can do pics, but never done video. It is exactly as I explained.
Alan

[boyt911sc]

Originally Posted by Alan L

Tony - I can confidently tell you - that is exactly what I am seeing. I have repeated it several times now. Same result. Fuel pump running = zero pressure on CIS gauge. I can let it run as long as you like - it does not change (I have the power to the WUR disconnected). (If I shut the valve I get Sys P.)
I turn the pump off with zero WUR pressure, and go back to the gauge and it sits about where the CP should be, and slowly drops to zero - over 1-2 mins. That is exactly what I am seeing.
Regards
Alan

Alan,

I have seen this phenomenon many times too when the control pressure is about 2 bar with the fuel pump running and after you turned off the FP, the gauge reading goes up. This is the effect of the FUEL ACCUMULATOR diaphragm decompression. The smaller FA on my CIS bench tester has 25 psi. decompression pressure. But never on a ZERO reading.

I will test a different FA (bigger) and observe where the decompression # settles.

Tony

[Alan L]

Hi Tony,
I can confirm it must be the FA. I have pinched the one off my 930 (no easy task - pic. If you thought the 911 was tricky......).



I don't have a confirmed source for a local FA yet and delivery from one o/seas is suggested early/mid July. So desperate measures - I want to use the car before I depart o/seas for months in early July.
Once I swapped the 930 one in (same as 911), everything has gone back to normal, other than some small WUR tweeks, and I had to raise the pin 0.4 bar and tweek WP back a bit.
I have cut the old accumulator open. Hard to see any obvious issue. But it was bleeding air, and I had already replaced the system pressure O ring and the pump check valve - to no avail.
I can only think it was spilling too much fuel via the bottom port to register a pressure in the WUR. It could register a system pressure against a locked return loop, but not an open loop thru the FD.
Regards
Alan