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Excessive control pressure (combines Inside the WUR and fuel cell height & CP)

Started by Feather535, 05 February 2023, 11:46 AM

Randys01

Pardon me if i'm not full bottle on your project but have you had the "slug" apart.?
 If so.    Is the O ring in tact? The foil valve in place? Is the inlet mesh filter crystal clean?

Feather535

Quote from: Randys01 on 09 May 2023, 02:55 AMPardon me if i'm not full bottle on your project but have you had the "slug" apart.?
 If so.    Is the O ring in tact? The foil valve in place? Is the inlet mesh filter crystal clean?

No worries!  Thanks for following this thread.

If the "slug" is the assembly in the picture on page 1 of this thread (I hear it called the fuel pressure regulator), yes, I've cleaned it and replaced all the o-rings.  I also replaced the inlet mesh filter on the fuel distributor and cleaned it again in repeating the whole diagnostic sequence with the WUR.  I don't know what the "foil valve" is. 
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Randys01

The slug is the valve body fitted in the WUR to which the inlet and outlet fuel lines are connected. Looking from the inside of the WUR there is a ceramic /fibre type disc with small hole in it. This hole is to allow the pin influenced by the bi metallic strip to adjust the fuel pressure by vituue of a silver film foil and an O ring embedded in side the slug. This assy is held to the slug with 4? screws.
Have you been in here? This is where I think your problem might lie.

daantjie

I think I posted this link before, but this is a pretty good overview of what is involved:

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

Daniel
1977 450 SEL 6.9 - Astralsilber

Feather535

Quote from: Randys01 on 10 May 2023, 02:45 AMThe slug is the valve body fitted in the WUR to which the inlet and outlet fuel lines are connected.

We're working with different nomenclature here-that assembly is the fuel cell to me-but I did work on it. 

I removed the bimetal strip, springs, hat, pin, the 4 screws and plate and the foil diaphragm and the o-ring underneath.  Then I the soaked the whole assembly in solvent for a week and afterward blew out the orifices with compressed air.  I reassembled the unit with new springs, a new o-ring and a new foil disc.  After all that I was able to get the pressure settings right for a short time, but after starting the engine a couple of times, the control pressure climbed back up to about the same as system pressure.  Since then I've disassembled and cleaned the WUR several more times, but I can't get the pressures back down to where they should be. 

Pretty frustrating, I gotta say.
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Feather535

Quote from: daantjie on 10 May 2023, 11:39 AMI think I posted this link before, but this is a pretty good overview of what is involved

Yep, watched that and did the whole procedure as described. 
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Randys01

ok.,.good man..sounds  very thorough. Seems as tho your pressure  build up is further up the line OR  do you havea full time vacuum line attached to the WUR upper chamber by accident?

raueda1

This story is very frustrating and I feel your pain. Somehow my gut tells me that there's an odd, recurring problem with crap in the fuel system that keeps clogging things and creating back pressure. 

Are you absolutely certain that the fuel return lines and rubber hoses are clear?  And when you cleaned the fuel tank was there rust silt inside? No doubt there was, but maybe there's residential that is getting stirred up? And have you replaced the rubber return house between the tank and the return line?  Even if you can blow it out with compressed air there can still be enough back pressure to cause problems.  Can't hurt to replace it off you haven't already.

Maybe test a couple things. 1. Disconnect the fuel line at the FD and collect, say, a gallon of fuel in clear container.  Is there any sediment at all?  2. Try the same on the field return.

Also, in cleaning out the slug and replacing the o-ring, did you polish the surface of the slug?  I can't remember if this was discussed.  If not then do so the next time it's apart.  Use high quality 2000 and 3000 grit paper successively to get a mirror finish.  And be sure that's the steel waters or manage or whatever don't have a dimple, otherwise replace. Obviously this won't solve back pressure but the WUR will work better.

I have a feeling that eventually there will be an "ah ha" moment here.  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 11 May 2023, 03:15 AMThis story is very frustrating and I feel your pain. Somehow my gut tells me that there's an odd, recurring problem with crap in the fuel system that keeps clogging things and creating back pressure.

That's for sure.  I've been going around in circles chasing this problem for months. 

There was some rust in the tank, but not as much as I expected. The more alarming finding there was the fine-grained tan-colored silt clogging the outlet screen.  It was the same stuff I found in the inlet screen of the WUR after the control pressure started climbing again. 

Of course I replaced the screen in the tank, and the return hose between the hard line and the tank. And just yesterday, I check the rubber return line from the FD to the hard line off (again) and verified that I can blow air through it.  That line is obviously old and doesn't look great;  I'd replace it if I could find a new one, but it's probably ok.

Inside the WUR, the foil disc looked ok when I took it apart for the first time, but I replaced it anyway, along with the o-ring.  But I didn't polish the surface. 

And I haven't collected a fuel sample since cleaning the tank.  I suppose that's worth doing, but sending the WUR out to be rebuilt is beginning to look inevitable.  I'm reluctant to spend the money, but even the factory manual says to test with a known good unit if the CP is too high. 
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

ramiro

Just a note about sending out them to be rebuilt , in Germany i had 2 WURs send to 2 different companys  1 had to be returned 3 times before the pressure was fine , the other one was completly out of adjustment after 1 year , thats why i started to adjust them myself because spending so much and still having problems is not worth it.

If your control pressure is at system pressure with a empty WUR it really shouldn't be to hard to find the issue i think.

daantjie

Daniel
1977 450 SEL 6.9 - Astralsilber

Feather535

Has anyone used k-jet specialists (www.k-jet.biz) in Australia?  Their service looks a bit cheaper due to the exchange rate.
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Randys01

Yes. I've used them for WUR and fuel dividers some years back.
I could not speak to their current performance but have no reason to doubt them .

REcon a WUR is... for a pro..., a piece of cake.

The exchange rate is a bonanza for you. It's killing us sending stuff to the US or buying it from there.....and so is the freight either way.!!

As your story has unfolded I'm inclined to think the problem lies not in the WUR but back in the fuel divider.

raueda1

Quote from: Randys01 on 19 May 2023, 03:27 AMYes. I've used them for WUR and fuel dividers some years back.
I could not speak to their current performance but have no reason to doubt them .

REcon a WUR is... for a pro..., a piece of cake.

The exchange rate is a bonanza for you. It's killing us sending stuff to the US or buying it from there.....and so is the freight either way.!!

As your story has unfolded I'm inclined to think the problem lies not in the WUR but back in the fuel divider.
Randy, is the fuel divider the same as the damper - the round thing between the WUR and FD?  You're way ahead of me on all this, but if so then I'd agree.  Problem seems related to a recurring source of silt.  The damper might be such a source, leading to repeated reclogging.  Or it could just be defective which might do the same thing.  Maybe try bypassing it and see what happens?
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Feather535

Quote from: raueda1 on 19 May 2023, 07:09 AMThe damper might be such a source, leading to repeated reclogging.  Or it could just be defective which might do the same thing.  Maybe try bypassing it and see what happens?

I thought of this.  I have tested control pressure with the gauge connected directly between the fuel distributor and the WUR, bypassing the damper, but the pressure is the same as with the damper in the circuit.

On the other hand, if the fuel divider is the fuel distributor, I have only done the following there: replaced the inlet screen and the o-rings in the pressure regulator; ensured the passages on the return side are clear.  Not sure what else I could do, but open to suggestions.
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)