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Inside the WUR

Started by Feather535, 18 December 2022, 08:27 PM

Feather535

I'm disassembling the WUR from my 280SE in search of the cause of excessively high control pressure (always about 5.5 bar, warm or cold).  I suspect a restriction on the return side and according to raueda1 there is a little screen inside the WUR that can get clogged and cause that to happen.

I've removed the bimetal strip, the springs and the little pushrod, and the circular cap and 4 screws beneath that.  Under that is a steel cylinder: on the inside face is a small diaphragm, and the fittings for the fuel lines screw into the outside face.  But now I don't know what to do.  It's not obvious how to remove the diaphragm, and I still don't see where the fuel comes into the WUR and goes out.   In fact, from the outside, the port for the return line looks like a dead end, while the one for the inlet has a small orifice at the bottom.

A diagram of this device would be a big help.  Can anyone explain how to get access to the fuel passages and that screen, if it's really there?

daantjie

Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

Check out this courtesy of Daniel from another post.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Feather535

Quote from: daantjie on 18 December 2022, 10:00 PMHere is a good video that'll help you:

https://m.youtube.com/watch?v=VVsnF2RlEqw


Kent from Mercedessource has also done a pretty good video that's a lot shorter https://www.youtube.com/watch?v=UoNw47wI8E8

Feather535

Now I've taken most of the WUR apart and I can see that the screen inside the large fuel fitting is plugged up. It's so bad that at first I didn't recognize that actually is a screen.  But it's hard to see how to get access to the screen to clean it. Seems like the fuel cell would have to come out, but it's not clear how to remove the fuel cell or whether even that would make the screen accessible.  Ideas?

ramiro

I usually just blow throught it with compressed air from the other direction.
Removing the fuel cell will not change the access i think , but removing the fuel cell will change the pressures because the warm control pressure is adjusted by tapping in or out the fuel cell , allthough i am pretty sure it has to be readjusted after dissasembly anyway.

raueda1

Quote from: ramiro on 22 December 2022, 06:48 AMI usually just blow throught it with compressed air from the other direction.
Removing the fuel cell will not change the access i think , but removing the fuel cell will change the pressures because the warm control pressure is adjusted by tapping in or out the fuel cell , allthough i am pretty sure it has to be readjusted after dissasembly anyway.

Yes, all this.  A couple further points.  The steel diaphragms really need to come off the cylindrical fuel cell to clean it all out, but I guess this is already done.  So, also try using carb cleaner to loosten the junk inside filter.  It might be time to just buy a rebuild kit.  They're available on ebay.  Then you can also replace the o-ring under the diaphragms as well as the diaphragms themselves.  If the diaphragms are slightly distorted or bent (pretty likely after years of use) then they should be replaced.

As for knocking out the cell, you might as well just do it.  It's almost certain that it will need to be reset anyway, so why not?  Then you can also repolish the bottom per link above.  Use 3000 grit paper to get a mirror finish.  Take a picture so you know approximate cell positioning when putting it back together.  And don't get discouraged.  You'll likely do a lot of in-and-out-again before getting pressure set up right.  That's just a fact of life (and also why there are so many posts about making your WUR adjustable).  Keep posting progress!
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

There's also this one:
[another wur video]https://www.youtube.com/watch?v=zW5qV208tCA[/url]

This guy polishes the screw-on valve cell cover but not the face of the valve body itself (where the orifices are).  Seems a but odd - pressure will doubtless need resetting, so why not do the whole job?
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

SteveDuNord

Does anybody know where I can buy the retaining clip for the electrical connector to the WUR?

I appear to have lost mine.
'77 280se

Feather535

Quote from: raueda1 on 22 December 2022, 01:57 PMYou'll likely do a lot of in-and-out-again before getting pressure set up right.  That's just a fact of life (and also why there are so many posts about making your WUR adjustable).  Keep posting progress!

Sadly, that seems to be what's in store.  Since my last post, I replaced the o-rings in the fuel distributor using the kit from raueda1, removed and disassembled the WUR, soaked it in solvent for 2 weeks, and put it back together using the kit from k-jet.biz.  At first, the screen on the inlet side of the WUR was obscured with sediment, but after cleaning it looked clear and I could blow compressed air through the fuel cell fittings. 

I was feeling optimistic that clearing the screen would fix my problems, but when I reinstalled the WUR yesterday, nothing had changed  :-X That is, the control pressure is 5.5 bar warm or cold and the engine runs lean.

So what next?  Push in the pin holding the bimetal strip?  Replace the pressure damper in the inlet circuit?  Reset the fuel cell height?  Take the WUR apart again?  It seems like I'm starting over from zero.

revilla

Hi,
Can you send us a picture of your pressure gage setup when measuring both control and system pressure. With that kind of CP your engine wouldn't even start. The piston won't move even one mm upwards to let fuel flow into the injectors. Do not hammer the plates/pins for now. That might get things worse if we don't understand what's going on with the measurement method first.
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]

Feather535

Quote from: revilla on 29 January 2023, 03:22 PMCan you send us a picture of your pressure gage setup when measuring both control and system pressure. With that kind of CP your engine wouldn't even start.

The engine does start, but not easily, and it's clearly running much too lean. 

I'll post a picture as soon as I can figure out how.

Feather535



I hope this is clear enough.  The valve is on the hose connected to the hard fuel line to the WUR.

Feather535


rumb



I'll post a picture as soon as I can figure out how.
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