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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

Feather535

I initiated 2 threads related to excessive control pressure that had grown to multiple responses over 2 pages.  To reduce confusion going forward, I'm starting a new topic, beginning with a summary of the problem and what I've done so far. This is part 1.

The car in question is a 1977 280SE, sold new in Los Angeles California.  It hadn't been  on the road in 10 years when I acquired it.  The seller had replaced the fuel pump and filter, distributor cap, spark plugs and wires and got the engine running, but the car wasn't drivable.

The problem I'm trying to solve is lean running.  The engine is hard to start cold.  When it does start, it pops back through the airflow plate and dies if the throttle is opened.  When the weather was warmer, I could keep the engine running long enough to reach operating temperature and then it ran well enough to drive at low speed. I haven't been able to do this now with cold weather and snow.

Before considering fuel injection, I eliminated other potential causes, mainly vacuum leaks and ignition timing. 

The fuel delivery volume is adequate and base system pressure is 5.5 bar. The cold start injector is working. I have gone through the rest of the test sequence in the CIS Diagnosis and Adjustment manual and it passes all tests except these: cold control pressure = 5.5 bar, warm control pressure = 5.5 bar, full load vacuum enrichment 5.5 bar.

Since then I removed the WUR, disassembled it, cleaned the screen on the inlet side and reassembled it with new parts from k-jet.biz.  Because the inlet screen was visibly plugged with sediment, I was optimistic that this would restore the correct CP, so I didn't try to reset the fuel cell height, which is about 2 mm above the WUR surface.

Now the WUR is back on the car, but nothing has changed: CP is still basically the same as system pressure.

This is already long, so I'll describe the latest tests in Part 2.

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

Feather535

This is Part 2.  The cleaned and reconditioned WUR is back on the car, but control pressure is still 5.5 bar cold.  The engine won't run long enough to test warm CP. 

revilla recommended 3 tests "Very slowly unscrew the return line at FD head...does the pressure go down? Repeat the same exercise...but this time unscrew the fuel pressure regulator on top/front of your FD. Lower pressure? Unscrew more but never completely. Pressure goes down? Same exercise but this time with the 12mm line on the side of the pressure regulator." 

When I do this the CP stays the same for the first and third tests on the return lines, but it goes down when the fuel pressure regulator assembly is loosened, going lower the farther it's unscrewed.  revilla thinks the FP regulator is the source of the problem and asked for a picture; here's one, and I can provide more. I replaced all the o-rings with new ones from raueda1.  There are 2 shims on the assembly.  I don't have a micrometer, but one is thin and the other is thick, about 1 mm.  And that's where it stands today...
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

revilla

Hi
Did you touch/change the 3rd and more difficult o-ring inside the chamber (allen hex screw) which is attached/sealed to the bottom of the small shaft? If yes, wad the tiny little clip that holds the nut and assembly together place back correctly? Does the shaft move freely?
What do you see inside that chamber when depressing the shaft? There are 3 lateral little holes to watch inside the chamber with light and magnifier.  3rd O-ring intact and in place, sealed to the bottom of the shaft?
Can you repeat your exercise of running the pump and unscrewing the 12mm line? Are you sure there's nothing coming out. Unscrew more and more (be careful). This line connects to the WUR which regulates CP, there should be fuel flowing there with pump running.
When you unscrewed the PR, how many turns, how much fuel and what do you read as CP? Does the car start with that lower CP (richer mixture). Careful with that fuel leaking, make sure you start with a dry rag and your ignition coil and cables are out of the way. If you aren't comfortable with this experiment please don't proceed.
The hypothesis we're testing is CP = SP = 5.5bars because the insides of the PR is blocking fuel from flowing to/from WUR. There are only 3 choices here (yes, no, partially). Need your results to continue or abort this hypothesis.
Have you cleaned the pass from PR chamber to 12mm lateral line? Open? Free? Again, with pump running there SHOULD be fuel leaking there. If not, we need to look closer to that line and inside PR. When you blew air through that WUR line, was is free flowing? Something is blocking fuel flow there? Let's find out what...

Feather535

Quote from: revilla on 05 February 2023, 10:35 PMDid you touch/change the 3rd and more difficult o-ring inside the chamber (allen hex screw) which is attached/sealed to the bottom of the small shaft? If yes, wad the tiny little clip that holds the nut and assembly together place back correctly? Does the shaft move freely?
What do you see inside that chamber when depressing the shaft?...
Can you repeat your exercise of running the pump and unscrewing the 12mm line?

I did replace the interior o-ring.  The tiny c-clip is in place and the shaft moves freely.   I checked that the holes on the sides are clear, but haven't looked inside.  I'll do that and then check again for fuel when the 12mm fitting is loosened. 
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Feather535

Quote from: revilla on 05 February 2023, 10:35 PMThe hypothesis we're testing is CP = SP = 5.5bars because the insides of the PR is blocking fuel from flowing to/from WUR. There are only 3 choices here (yes, no, partially). Need your results to continue or abort this hypothesis.

Understand the hypothesis and will go through the steps and report back. 

But we haven't talked about the inlet side of the WUR.  Seems like blockage in the inlet lines, the damper or the screen in the fuel cell could also cause high CP.  But if fuel is coming out, it must be going in, so this hypothesis could be ruled out if fuel comes out of the return line at the PR with the pump running.  Correct?
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

revilla

Correct.
If fuel doesn't flow out we'll look for the blockage upstream and downstream. Could be the inlet at wur, the be plate itself (valve), the inside of your FD, etc. We need to systematically look at every piece on the path. We'll find the problem.

Ps.: that little o-ring inside, are you sure is the correct size?
Its id/od/thickness are so precise! This thing is "like heat fusioned" to the bottom of the shaft from factory. If it moves it's disaster...

raueda1

Quote from: revilla on 10 February 2023, 12:28 AMCorrect.
If fuel doesn't flow out we'll look for the blockage upstream and downstream. Could be the inlet at wur, the be plate itself (valve), the inside of your FD, etc. We need to systematically look at every piece on the path. We'll find the problem.

Ps.: that little o-ring inside, are you sure is the correct size?
Its id/od/thickness are so precise! This thing is "like heat fusioned" to the bottom of the shaft from factory. If it moves it's disaster
...
I'll jump in on this.  OP got the o-ring from me.  I got a small lot of them and put one in my car after various CIS annoyances. See this (which may also be of interest to OP) In hindsight I was surprised that this issue hadn't been discussed here that I could find. Hope this helps and cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Feather535

I did a few more things. 

1. I removed the needle assembly from the FD again and checked the 3 small holes at the top to see if light could pass through.  It did, with or without the spring depressed, so I took it apart again and found the o-ring inside had come loose from its slot.  The original one had been stuck tight to the shaft and I unfortunately tore it up getting it off. 

2. Before putting the assembly back in the FD, I blew compressed air into the return port for the WUR and it came out the port where the needle goes, so apparently no blockage there.

3. With everything back in place and the fuel pump running, system pressure and control pressure are still the same -- but lower then usual: 4.8 bar instead of 5.5, which they always were before.  Strange!

4. I verified that fuel comes out when the 12mm fitting for the WUR return on the FP is opened.  But does this necessarily mean fuel is passing through the WUR and coming back? 

5. Loosening the needle assembly (16mm wrench) with fuel leaking will bring CP down to about 3.8 bar, but apparently no lower.  The engine will start and run in that condition.

For what it's worth, the ambient temperature was warmer when I did all this: about 10C (50F), instead of freezing.

This is a lot of data, but it hasn't gotten me closer to a solution yet.  I'll think about it, but hope you guys have some ideas. 
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Feather535

Quote from: Feather535 on 13 February 2023, 05:43 PM3. With everything back in place and the fuel pump running, system pressure and control pressure are still the same -- but lower then usual: 4.8 bar instead of 5.5, which they always were before.  Strange!

4. I verified that fuel comes out when the 12mm fitting for the WUR return on the FP is opened.  But does this necessarily mean fuel is passing through the WUR and coming back? 

Never mind number 3.  I discovered one of the shims had fallen out when I removed the needle assembly.  It's back in now and system pressure is back to 5.5.  So is CP.

To address my question in 4, I tried removing the 12 mm fitting on the FP again.  With the pump running and the gauge valve open, fuel is coming out of the port on the FD, not the line connected to the WUR.  I did the same test at the WUR end (small fitting) and verified that fuel is coming out of the line to the FD, not the small port on the WUR. 

Unless I'm confused about which way fuel flows through the control pressure circuit, this seems backwards.  I understood fuel should flow from the top of the FD, through the damper and into the big fitting on the WUR and return from the small port on the WUR to the small port on the side of the FD before going back to the tank.   Is this wrong?

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

ramiro

Yes the big fitting on WUR is the flow from the FD and the small is the return to the tank.
So you have fuel comming out at the WUR return port at the FD ?
I think that it is normal that fuel comes there out because it is also connected to the main FD return line to the tank but it shouldn't have any pressure.
Also if you turn the pump ofo there will be pressure because the return closes and the WUR will have pressure on both lines.

Feather535

Quote from: ramiro on 15 February 2023, 11:59 AMSo you have fuel comming out at the WUR return port at the FD ?
I think that it is normal that fuel comes there out because it is also connected to the main FD return line to the tank but it shouldn't have any pressure.

I suppose this makes sense, but there is no fuel coming out of the return port on the WUR with the pump running.

Wouldn't this mean that either 1) fuel isn't reaching the inlet side of the WUR or 2) it isn't flowing through the WUR?
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

ramiro

Just check if fuel is coming out the inlet(the one with the filter on the WUR) , if yes there is no fuel flowing through the WUR .

Feather535

I've done a few more things since my last post.   

1. Disconnected the inlet and outlet lines on the WUR one at a time and verified fuel is reaching the WUR and exiting it.  Control pressure is still too high, though—about 5.5 bar warm or cold—so I conclude the WUR could be partially, but not completely blocked. 

2.  Took the WUR apart again and cleaned it with solvent and compressed air.  While it was out, I pushed the fuel cell upward in the WUR body.  Before, only about 1 mm of the fuel cell was exposed; now it's about 4 mm. Also verified that the heater on the bimetal strip does actually get hot and that its resistance is in spec.   

3. Instead of reinstalling the WUR in its normal, inaccessible place under the M110 intake manifold, I rigged it up as shown in the picture so it's easy to remove and reinstall. 

4. First, I tested CP without the springs or the heater installed, so the WUR is basically just the shell of the top half holding the fuel cell. The gauge reads 0.7 bar and fuel is clearly flowing back to the tank—so progress there.

5. With the WUR reassembled and the fuel pump running, but no electricity or vacuum connected, the CP is still 0.7 bar, so in spec for the ambient temperature at the time (47 F, 8 C).

6. But, with the WUR's heater connected and the fuel pump-but not the engine—running, CP still doesn't increase, even after 10 minutes. 

Now, I guess this could be because at 8 C the WUR's internal heater alone, without engine heat, doesn't raise the temperature enough to change the spring pressure.  But it could also be because now the fuel cell is too high relative to the spring assembly.

So my dilemma is whether to punch the fuel cell down 1 mm or so and test again with the current setup or reinstall the WUR in its regular position (a nasty, time-consuming job) so I can start the engine and test warm CP with the whole system operating as normal.

Seeking the forum's advice while I contemplate next steps.

IMG_4299.jpeg
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

ramiro

I can confirm that even at below 0 C the electric Heater is enough to let the pressure rise just takes longer , but you can also take a heat gun to assist it.
It's no clear in the Picture but for me it looks like the pin that holds the bimetal strip is nearly at the top , that would explain why you pressure doesn't rise.
If it's not at the top i would suggest to tap it to the top and then adjust the fuel cell until you reach your warm pressure(i would go 0,2 - 0,4 bar lower first and make sure it is not rising more when you put the WUR back to its place) then you can adjust the cold pressure by tapping the pin for the bimetal strip in.

Feather535

Quote from: ramiro on 22 February 2023, 04:34 AMit looks like the pin that holds the bimetal strip is nearly at the top

You're right, the pin with the bimetal strip is down about 1 mm.  I will try again after tapping it all the way to the surface.

I did use a heat gun on the WUR.  It didn't cause the pressure to change, but maybe I didn't heat the WUR enough.
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)