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

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

Randys01

The fuel  damper and fuel divIder are two separate devices but our intrepid explorer has already eliminated the damper.
So now the attention turns to fuel divider..........err coff coff!

This contraption is the most exotic creation of the whole car. Now some people have had success pulling these apart and rebuilding them but I've not been one of them.

From the description of what's been done so far with the divider I'd say the problem lies in the build up of silt in the valving that reduces the system pressure to control pressure.

This is not a serviceable area with out a major pull down..........
I would not reccommend a home job on this......for me it's always a pro job becasue once it's apart there's a 100 parts.


ramiro

You don't have to take the fuel distributor apart to get to the pressure regulator , you can just take the whole pressure regulation piston out with 1 screw.
The rest of the fuel distributor should not really have any effect on the control pressure , only if somebody messed the hole up out that gives pressure to the WUR.

Randys01

The pressure regulator controls system pressure and provides a route for the returning control pressure
There is a more sophisticated valving device in the fuel distrb itself I do believe.

raueda1

Quote from: Randys01 on 20 May 2023, 12:41 AMThe pressure regulator controls system pressure and provides a route for the returning control pressure
There is a more sophisticated valving device in the fuel distrb itself I do believe.
Fuel Distrib = fuel divider?  If so there's lots of valving inside along with much more.  Also tiny internal filters under the tubing leading to the injectors.  They can be cleaned by pulling off the Tubing, though I doubt that's the issue.  Anyway, as far as FD goes, I strongly suggest not messing with it. I actually did manage to successfully rebuild it with help of a mentor.  However, I botched the reinstallation, caused fuel hydrolock, bent a rod and basically rebuilt the engine.  There are rebuild kits out there but far preferable to send it out to a rebuilder.  I think CIS-tech does it.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Feather535

So if I connected the pressure gauge directly between two ports on the fuel distributor that normally go to and from the WUR, but bypassed the WUR and the damper, would that tell me if something in the FD was causing excessive back pressure?

I have to admit that I'm not much inclined to send the FD out to be rebuilt. It looks like that could cost more than I have in the whole car.

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

Randys01

As a top rail mechanic said to me one day....  "CIS?...err that's a black science".

Yes..before the FD goes in for ohaul, I'd want to be sure all the ancillary equipment is playing ball.

Let's determine if there is any silt in the FD..

I'd be inclined to run the fuel volume test./fuel pressure test again. Let it pump thru into a clear vessel for as  long as you can.
Is there any hint of residue/silt/grunge in the fuel?

Is there a fine mesh filter in the fuel delivery line where it screws into the FD. or has this been removed?
Any anything caught  here?

Remove 2 fuel injector  lines and see if there are any filters in the top of the FD....carefully prise them out  if fitted] and see  if you can peer into the top of the FD and see any muck.
Gently push down on the air flap and see if any stuff comes out .

Remove and inspect the pressure regulator. Since it was last out is there any apparent signs of grunge?.

All clear? Then we have a known quantiy.No new grunge floating  BUT have not eliminated the possibility of some being stuck from a previous era.
I will have some more advice tomorrow....have to  a bit of research: but do what has to be done to answer the above questions b4going any further.


If all clear, then it safe to say there is no longer a threat of grunge going thru the system BUT it does not eliminate the possibilty of some being stuck form an earlier era.
If you get all clear on these tests,

ramiro

Quote from: Feather535 on 21 May 2023, 08:59 PMSo if I connected the pressure gauge directly between two ports on the fuel distributor that normally go to and from the WUR, but bypassed the WUR and the damper, would that tell me if something in the FD was causing excessive back pressure?

Thay you control pressure should definitly be close to 0 if not you have problem with pressure regulator (it also closes the return from the WUR when the pump is off) or return to the tank.

Feather535

Confirmed that pseudo-control pressure is zero without the WUR installed.  I think this indicates that excessive control pressure is originating in the WUR.

I also did the series of tests Randys01 suggested and didn't see silt in a sample of fuel from the pump, the inlet screen on the fuel distributor, or the tiny screens under the lines going to the injectors. 
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Randys01

ok..we'll take it that grunge is no longer a problem altho we can't say it hasn't been and possibily caused some residual blockage. Just park that thought.

I don't know what kind of fuel pressure test kit you have but I assume it has a flow vaLVE IN IT. I ALSO ASSUME WE HAVE IT CONNECTED SUCH THAT THE LINE FROM THE FD HAS NO VALVE IN IT......AND THE LINE FROM THE GAUGE TO THE WUR HAS THE FLOW VALVE ON THAT SIDE.
So with the flow valve shut we should have 5.2bar.

If the motor is cold and we open the valve we should have 1.3/5bar......and as we run the motor it should climb to 3.5 ... [WUR stablised]

So where do we part company?

Feather535

Quote from: Randys01 on 23 May 2023, 04:28 AMSo where do we part company?

After opening the valve. 

In the beginning the pressure was the same as system pressure: about 5.5 bar warm or cold.  Now, after disassembling and cleaning the WUR more times than I can remember, it's about 3.2 cold. 
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Randys01

Jeez.!!!I just wrote a  >:( full page in this and it disappeared :D
OK.abridged version.11 

Partially dismantle the WUR..with the fuel cell left in the top half, run the system press test  BUT massage the valve manually. If you get a variation in the readings, then you know it wants to work but all the devices that influence it are out of whack .

Anyway let's know.

Feather535

This is an interesting idea.  I tried something similar, but with the WUR assembled.  As I remember, the pressure was always the same as system pressure whatever the position of the valve.

Unfortunately, I can't repeat the experiment right now because I've sent the WUR off to be rebuilt. 

I'll report back on whether that solves the problem. 
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Randys01


Feather535

So here's the conclusion of this now very long thread.

I just installed the reconditioned WUR I ordered from k-jet specialists.  The cold pressure with the engine off was 1.2 bar.  That was all I needed to know, so I started the engine and...

it runs--strongly!  I've gone for a couple of short test drives now and this 280 SE which was off the road for 10 years runs and drives surprisingly well.

After struggling with the same lean running issue for months, I've learned a few things:

1. If all the evidence points to one thing being the problem, it probably is the problem;
2. It helps to test with known good components;
3. Sometimes you just have to spend the money.

Next step is to pass California smog.  Wish me luck!
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Randys01