911 sc cis residual pressure

[leonardo911sc]

Originally Posted by Schulisco

That long time delay is our enemy...the WUR should reach those 1,4bar asap, even after several seconds when engine fired up.

Could you make 2 videos with the fuel pressure gauge connected to see how the pressure behaves after switching off the engine?
1. control pressure (not important if the engine is warm, but the WUR should have reached the warm cp)
2. system pressure

Thomas

Originally Posted by Schulisco

That long time delay is our enemy...the WUR should reach those 1,4bar asap, even after several seconds when engine fired up.

Could you make 2 videos with the fuel pressure gauge connected to see how the pressure behaves after switching off the engine?
1. control pressure (not important if the engine is warm, but the WUR should have reached the warm cp)
2. system pressure

Thomas

Already done

1. Control pressure after switch off engine will drop to 2.5 bars and will maintain 1,3-1,5 bar after 30 min.
2. Warm pressure 2.8 bar without vacuum line connected and 3,4-3,5 bar with vacuum connected.
3. System pressure set to 5 bar.

Have posted all these before. With photos also.

Thanks

[ahh911]

Originally Posted by boyt911sc

Phil,

There is nothing wrong with the control fuel line. The fuel in the line would slowly seep out through the WUR after several hours. And would be filled up again in the next start-up. What is critical is to have the system pressure present immediately during start up. The control fuel pressure will come next after the system pressure.

To measure the system pressure in your CIS, you need the valve for the gauge closed and open for control pressure. This is the conventional way how the CIS pressure gauge is connected to your motor. You could leave the gauge installed and run the motor to measure the control pressure but NOT the system pressure. To overcome this problem, I installed 2 set of gauges. One for the control pressure and one for the system pressure.

So at any given time the motor is running, I could monitor both control and system pressures simultaneously. But this is not for everyone. Unless you have a curious mind.

Tony

Thanks Tony,

I don't have two fuel pressure setups, but it sounds like the only way to confirm system pressure is coming up in running/starting mode while observing the control pressure as well.

As a question, my system pressure was about 4.4/4.5 bar, on the edge of spec. I've seen many others with this type of system pressure on the board. What benefit is there to increasing the system pressure that you have seen (in terms of start/drivability) for a cis car? Also, I guess that increasing the system pressure 10% will also increase the control pressure 10%? If so, then a low system pressure would have the warm and warming up control pressure set to the low side as well for optimum warmup and then driving? By the way, the lambda shows 45% Duty when driving around 3000 rpm, I'd like to keep it that way which I assume is a function of the system vs control pressure once warm of course and if one is adjusted, I'd adjust the other to maintain the 45% at roughly 3000rpm I'd think. Is most of this the way you understand it? Do you have any advice/comments/recommendations?

Phil

[leonardo911sc]

Good day Phil.

Testing value is 4.5 to 5.2 bar

But

Adjusting value is 4.7-4.9 bar

Above is for 089 WUR.

Check your WUR datasheet.

[Schulisco]

Phil,

just a hint for understanding - George/leonardo911SC owns an '81 euro spec 204hp ROW 911 SC without lambda control and - I suppose - without catalyst...

But I personally own an '81 US spec SC with lambda control. I can confirm that my SC also doesn't reach 5bar fuel system pressure. The duty cycle on my SC while cruising is also somewhere in the 40 duty cycle. So pretty close to yours. It might be that an increase of 10% system pressure also rises the control pressure. Never tried. Would be an interesting experiment.

But - the tolerances on this CIS system are not very narrow. E.g. the WUR cotrol pressure diagram shows always a range of pressure. In general this is +-0,2bar, in sum almost 0,5bar between upper and lower value on a given ambient temperature. Also for the system pressure. Those systems aren't that precise. The injectors have also a range of opening pressure between 2.5 and 3.6bar, so pretty wide. The individual setup on every single system is balancing this out. So it's quite important to folow the rules on adjusting first and foremost the sensor plate height (must be very precise! If not, it will make a huge difference!), then the CO value as given in the manual and lastly the idle rpms. All values on a warmed up engine only. If you keep this sequence of adjustment should you hit the mark...

Thomas

[leonardo911sc]

Good day to everyone!

So since control pressure will not raise during cranking i decided last night to go crazy and bypass the WUR as part of my troubleshooting.

Simply i connected my pressure gauge to FD outlet and WUR outlet lines. I run the pump and set the pressure to 1.4 bar by adjusting the gauge valve.



Here is next morning cold start...
https://youtu.be/r3iP1BHkuS8

[Schulisco]

[leonardo911sc]

Will check WUR diaphragm.

[Showdown]

The WUR, because of the fine mesh and close tolerances seems to be vulnerable to any debris, sediment, or contamination more so than any other component.

When I rebuilt mine, I found that simply cleaning it out radically changed start ups. And it wasn’t all that dirty…

It may take a few tries to get the tightness of the diaphragm correct, but don’t despair, you’ll get it eventually.

[leonardo911sc]

Good day!

So i opened the supposed rebuilt WUR.

There were traces of fuel leak into the chamber. I didn't find any liquid but stains of dried gasoline. Check the white stains in WUR body and diaphragm outer perimeter at the photos below

Removed the new fuel diaphragm and compared it with an old genuine i have from a spare old used WUR i have.

My only observation is that the new steel diaphragm feels softer than the genuine. My digital caliper is out of order so can not measure thickness to compare.

Cleaned thoroughly the old genuine diaphragm and installed it with new o- ring.

Cold / warm pressures needed re adjustment.

Engine fired this morning with half crank.

I will not declare this case as solved yet. Will test for a week first.

[ahh911]

leonardo911sc/ George,
Thank you for the update, please keep us informed.

Phil

[Funracer]

Best thread I have read this year. Great problem solving and pictures/vids to bring us along. I had forgotten you can bypass the WUR and use the fuel gauges manual valve to control pressure as a troubleshooting measure. When you are satisfied this fixes your start issue please let us know.

[Schulisco]

Originally Posted by Funracer

Best thread I have read this year. Great problem solving and pictures/vids to bring us along. I had forgotten you can bypass the WUR and use the fuel gauges manual valve to control pressure as a troubleshooting measure. When you are satisfied this fixes your start issue please let us know.

This is just one way of narrowing down the cause of the error. It's not a permanent solution! The only permanent solution is to fix the WUR!

I haven't personally done it, but from what I've heard you might need a few tries. There are afaikno specified torque values for the valve screws available.

Thomas

[Funracer]

Originally Posted by Schulisco

This is just one way of narrowing down the cause of the error. It's not a permanent solution! The only permanent solution is to fix the WUR!

Thomas

Of course. But a nice troubleshooting procedure for future reference.

To summarize, even though the WUR CP was within spec, it was not getting to that number in a timely manner. This caused too rich mixture for the first 10-15 seconds for a smooth start. Started faster with the CSV removed from the system was a clue.

Always more to learn on these CIS things.

[ahh911]

Hopefully it's solved,

What still is puzzling:

1. Video test when air was introduced into the FD to WUR line and the control pressure was at zero (max richness) and the CSV was attached, it started up right away and surged.
Repeatable?

2. Video test when the line was primed, the control pressure started higher and increased almost twice as fast as 1. above, it did not start. CSV was attached.
Repeatable?

3. The metal diaphram if plugged, should increase the initial control pressure, not lower it. How does control pressure start off lower? The leaking gas stains around the wur, was it a leaking diaphram indeed emptying the FD to WUR line? The residual control pressure test should have shown this or was it too small a leak, or is control residual not tested? Is Thomas right it should drip when removed 12 to 24 hours later? Tony says it doesn't matter, mine is dry but assumed to have negative pressure and starts fine but just one data point, but Tony Highlighted that is is Normal that the line could be dry but not because of a leak in the WUR to the outside world.

4. George mentioned it started first time after many days, wouldn't the pressure have further dropped in the system? (Repeatable?)

Let us know when things are stable what you think George, it will be useful.

Phil

[Showdown]

It's always the god-forsaken WUR... UGH.

Glad that it's fixed... just in time for the CIS to throw you another mystery. Fun times!!

[Showdown]

It's always the god-forsaken WUR... UGH.

Glad that it's fixed... just in time for the CIS to throw you another mystery. Fun times!!

[leonardo911sc]

Hi Everyone!

It is the third day of testing. No issues with cold starts.

See below video

https://youtu.be/FZ0GIcQh4dk

[leonardo911sc]

I just have one technical query which i personaly can not explain.

Since this was a WUR pressure build up isuue during cold start causing an over rich condition , why same happened even when i was priming the system by activating the pump? This was supposed to ballance the pressure of the system prior starting the engine.

Food for thought

[leonardo911sc]

Let me reply to the above.

Although the engine now starts every time anytime, at cold starts the smell of rich mixture was noticable.

A couple of hours ago i went for a routine service before i deliver the car to my best man. Lubricant, oil filter and air filter.

When i removed the air filter i went and pushed up the sensor plate. It took about 5-6mm until the resistance of the plunger was felt.

Repeated the push up a couple of times to realize that the plunger was not resting on the sensor arm completely.

After about 10 times of moving the arm up and let it relax it finally rests on the arm and resistance can be felt from the begining of the lift.

Now gas smell is also gone at cold starts.

This is also the reason why in the begining of this thread i mentioned that the engine will not start after 9 hours but it may start after 2 days!

I suppose the plunger eventually would rest on the arm over time and gravity effect.

So my culprit was a combo of CIS components not working properly.

Now officially this case is solved.

Thanks everyone for your assistance and knowledge passed.

[ahh911]

George,
How do you plan on fixing the sensor plate plunger not sitting in rest position?

Please keep us informed of this, it's very interesting, I'm glad you're solving this... Now I know a little more.

Phil