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WUR fuel cell height and control pressure

Started by Feather535, 29 January 2023, 12:57 PM

Feather535

I have a questions about next steps after cleaning and refurbishing the WUR on my 280SE failed to solve the problem of excessive control pressure.  It's my understanding that driving in the pin that secures the bimetal strip reduces control pressure by relieving spring pressure on the fuel cell diaphragm.  So it seems that increasing the height of the fuel cell should have the same effect: longer distance => lower pressure.  Does that make sense? 
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1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Randys01

It doesn't seem to matter what you do, the control pressure when hot remains the same.ie elevated at 5`bar.

So what is the CP when cold?..1 to 1.5 bar?
What happens as the motor warms and the control pressure starts to rise?.ie creeps up to 3.6bar but keeps going. ?

ramiro

Driving in the pin that holds the bimetal reduces the cold pressure , and driving in the fuel cell increases the warm pressure
The right procedure to adjust them is to drive out the pin that holds the bimetal to the top(that way it has no influence and you can adjust the warm pressure) and also drive the fuel cell out 3 - 4 mm , then connect the wur and adjust the warm pressure by tapping in the fuel cell , after that you can adjust the cold pressure by driving in the pin.
But be sure that everything around the wur is fine before doing that.

Feather535

Quote from: Randys01 on 30 January 2023, 09:37 PMSo what is the CP when cold?..1 to 1.5 bar?
What happens as the motor warms and the control pressure starts to rise?.ie creeps up to 3.6bar but keeps going. ?

The CP stays around 5.5 bar warm or cold, vacuum attached or not.
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Feather535

Quote from: ramiro on 31 January 2023, 05:50 AMDriving in the pin that holds the bimetal reduces the cold pressure , and driving in the fuel cell increases the warm pressure.

Thanks.  This answers my question.  The pin is already down about 2 mm and the cold pressure is too high, so does it make sense to drive it in further?  I'm a bit reluctant, since I'd have to take the WUR apart again and reset the pin if that doesn't work.
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

ramiro

If the Pressure is also 5.5 when the WUR is warm it makes no sense to change that pin , because it only affects the cold pressure.
If you are sure that everything around the WUR is ok suggest doing the procedure i described above to adjust the pressures.

Feather535

Quote from: ramiro on 01 February 2023, 08:17 AMIf the Pressure is also 5.5 when the WUR is warm it makes no sense to change that pin , because it only affects the cold pressure.
If you are sure that everything around the WUR is ok suggest doing the procedure i described above to adjust the pressures.

Makes sense, thanks.
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Randys01

Ramiro is correct in his setting up procedure...go with that.
I would suggest...irksome I know...that whilst you have it apart for the tenth time., you check that the metal film valve in the fuel cell has not been damaged. You don't have to remove it from the WUR body...it's 3 or 4 screws to peak a look.

revilla

The procedure is correct.
BUT...
Think well before tapping on any of the 3 settings points of your WUR.
There are especially 3 things to consider before making that decision.
1) How did the WUR ended up in such condition to have 5 bars of CP. It takes a lot of tapping to get there. Never seen one that needed this huge amount of calibration.
2) The procedure is in fact simple. But it requires steady hands to get it right-first-time.
3) What if tapping doesn't solve the problem? You've recently been in the situation.

Tapping in/out for corrections will at one point damage your device.  It can take a few adjustments in 40 years. But it's not a robust enough design to get three sessions of tapping a week. It'll certainly get damage under that type of abuse.

But this is your WUR and your car, so it's your decision.

I suggest we understand where the problem is coming from first, before start tapping in a let's-throw-the-dart-in-a-dark-room approach, cross fingers and get lucky.  I have never seen that work before. Low probability. Rather let's understand the root cause of the problem first. Just my suggestion.
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100][url="http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG"]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/url][/img]

raueda1

Quote from: revilla on 03 February 2023, 12:45 AMThe procedure is correct.
BUT...
Think well before tapping on any of the 3 settings points of your WUR.
>>>snip<<<

I suggest we understand where the problem is coming from first, before start tapping in a let's-throw-the-dart-in-a-dark-room approach, cross fingers and get lucky.  I have never seen that work before. Low probability. Rather let's understand the root cause of the problem first. Just my suggestion.
I agree.  I've been out for a while and it looks like a lot more has gone on and we're now to 2 threads on the topic.  Feather535, at this point it might be helpful to take a step back and summarize what's been done thus far and the results to date (though I guess that's mostly "tried XYZ but didn't help").  Otherwise we may end up just repeating ideas that were already tried but lost in much earlier posts.  Might make it easier for people to help.  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Feather535

Quote from: raueda1 on 03 February 2023, 10:01 AMit looks like a lot more has gone on and we're now to 2 threads on the topic.  Feather535, at this point it might be helpful to take a step back and summarize what's been done thus far and the results to date

Good idea.  I'm going to start a new thread combining this one and Inside the WUR and provide a summary of what I've done so far.  Stay tuned.
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)