News:

www.W116.org - The #1 resource for our W116! Established 2004

Main Menu

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

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

ramiro

If it's so far up it is normal that the pressure is not rising because the bimetal has no effect like that , and thats also the purpose because you can now adjust the warm pressure to ~ 3,2 by tapping the fuel cell in and then you can lower the pressure down with the bimetal.

The idea is that the bimetal strip should have no effect when the engine has warmed up thats why you should tap it out to adjust the warm pressure to be sure that it won't mess with the pressure and only then adjust the cold pressure.

Feather535

I followed this procedure.  First I drove the pin for the bimetal strip up to be flush with the top of the WUR, then tapped the fuel cell down about about 2 mm above the top (starting at 4 mm), then tapped the pin for the bimetal down again.  Now I have 0.9 bar cold at about 3 C and 3.1 bar warm after 6 minutes with the heater plugged in and using a heat gun on the outside of the WUR for a few more minutes. Both settings are in spec for the temperature when I did this (3 C) and the model (California, 1977), so this should be good enough.

Now I need to put the WUR back in it's normal place and see how the engine runs, but that's a job for a warmer day!
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

ramiro

I hope that you measured the pressure and adjusted it to the around 3.1 bar before you tapped the pin back in, because if not it is possible that the bimetal is affecting you warm pressure and it could rise further on a hot engine (i made this mistake before knowing the procedure and nearly went crazy because the warm pressure was always changing).

Feather535

Quote from: ramiro on 26 February 2023, 06:21 PMI hope that you measured the pressure and adjusted it to the around 3.1 bar before you tapped the pin back in

That's how I did it.  I had 3.2 without heat before tapping the pin down and 3.1 with heat afterward.  Seems good?
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

ramiro

Should be good then , i don't know if you have full throttle enrichment on the WUR if yes then this is the full throttle control pressure , so at no load it will be ~ 0.2 - 0.4 higher , because the vacum is pushing the control rod up.

You can use a vacum pump on the top vacum connector to replicate this without the engine running.

Feather535

Quote from: ramiro on 27 February 2023, 04:38 PMShould be good then , i don't know if you have full throttle enrichment on the WUR

It does have full throttle enrichment.  Pulling vacuum makes the pressure drop.  I didn't record the pressure with vacuum, but it's moving in the right direction, so the mechanism seems to be working. 

Next step is to test it on the car with the engine running, but I'll need to wait for the snow to stop.  Can't even get to the garage today!
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

ramiro

The vacum makes the pressure higher and when the engine is at load there is no vacum in the intake so the control pressure will decrease.
The vacum port is at the top , the other at the bottom is just the vent port that goes before the throttle body.

Feather535

Quote from: ramiro on 28 February 2023, 04:26 PMThe vacum makes the pressure higher and when the engine is at load there is no vacum in the intake so the control pressure will decrease.

Of course.  I'll check it again.
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Feather535

I've been offline for a while because I haven't had much time for working in the garage.  But recently I drained, removed and cleaned the fuel tank (1977 280 SE, California model) and replaced the screen in the bottom of the tank, the accumulator, the filter, and all the hoses in the rear of the car.  Before that, I had removed the WUR (again) and cleaned it (again) after discovering that the inlet was full of sediment (again). 

So today I finally put the WUR back on and tested the pressure.  I was hopeful, because I had gotten it about right earlier this year (1 bar cold, 3.8 running) after thoroughly cleaning and recalibrating the WUR.  But then the cold pressure crept up to where it had before (5.2 bar) after running the engine for a little while.  I thought this must have been because the inlet was clogged again.

But no luck.  The cold pressure is still 5.2 bar, even with nothing installed inside the WUR except the diaphragm, and with the fuel cell standing about 5 mm above the top of the WUR. 

Gotta say, I'm getting pretty tired of this. 
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

ramiro

If even without anything inside the pressure is 5.2 bar something must be clooged , either the return line or something that got behind the mesh in the WUR.

daantjie

Daniel
1977 450 SEL 6.9 - Astralsilber

Feather535

Quote from: daantjie on 07 May 2023, 10:48 AMMight be time to swap in a known good WUR.

That's what I'm thinking.  Unfortunately, I don't have one and don't know anyone nearby who does, so that probably means buying a refurbished unit. 
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

daantjie

Quote from: Feather535 on 07 May 2023, 11:59 AM
Quote from: daantjie on 07 May 2023, 10:48 AMMight be time to swap in a known good WUR.

That's what I'm thinking.  Unfortunately, I don't have one and don't know anyone nearby who does, so that probably means buying a refurbished unit. 

Sometimes you can find a NOS one on ebay but usually they are priced quite high.  Also need to make sure to get the right one as there are many variations over the years and models.
Daniel
1977 450 SEL 6.9 - Astralsilber

Randys01

I'd be wary of buying a 2nd hand one because it's probably stuffed. caveat emptor.!
You would do better to have yours refurbed. There are several coys near you ie in the USA that do these.....spend the money. You also know that unit is the one for the car [hopefully it's the orig ]

You cannot frig around with the injection on these 50 year old cars like a 3psi Carter on a Chev Belair.!!
The furb unit will last you 20 +years and you can confidently remove it from the list of possibilities going forwrd. What's  more you might get a clue from what they find is wrong with it.




btw .If you suspect crud in the fuel, how do you know the pressure you are reading is not actually fuel pressure build up in the fuel divider?  I gather you've had this WUR apart a 100 times but you need to know is the hi pressure  something to do with the WUR or is a fault further upstream. ? it seems the problem is when it gets warm/hot.the psi rises to full system pressure in stead of a controlled pressure.
It seems the vbalve in the WUR is going nearly to fuully closed. IOf all things arte equal, the only way it do that is if the bi metallic strip is over reacting?



Feather535

Quote from: Randys01 on 08 May 2023, 03:57 AMIf you suspect crud in the fuel, how do you know the pressure you are reading is not actually fuel pressure build up in the fuel divider?  I gather you've had this WUR apart a 100 times but you need to know is the hi pressure  something to do with the WUR or is a fault further upstream. ? it seems the problem is when it gets warm/hot.the psi rises to full system pressure in stead of a controlled pressure.

Well, there could be crud everywhere in the system, it's true.  But I did a test and found there was fuel going to the WUR but basically none coming out the return, so I concluded the thing had to be clogged.  And actually the COLD pressure is nearly the same as system pressure, even with the springs and bimetal strip removed from the WUR, so those bits aren't the cause.

Only other thing I can think of is a clog in the inlet line or the damper.  I think I tested those too, but will do it again before springing for a rebuilt WUR.

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