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280se - new to me, warm stalling!

Started by SteveDuNord, 04 May 2022, 10:57 AM

SteveDuNord

Quote from: raueda1 on 21 June 2023, 06:51 AMExactly.  If fuel return in blocked or restricted too much then [system pressure] = [control pressure].  So check this first before going down the WUR rabbit hole.  Blowing compressed air through the return is just one way. You can try just blowing through the return tube but that's very hard to do and you need to blow out the fuel in the line before hearing bubbles in the tank.

Here's another way:  disconnect the fuel return line from FD.  Hook up a tube out of the FD into a container, similar to the fuel flow test.  Run fuel pump and check pressures.  If the fuel return is blocked AND the WUR is actually OK then your control pressure should now be ok cause you removed the cause of the back pressure against the system.  Hope that makes sense.  There's no guarentee that this will solve the problem, but it's easy.  And if fuel return is constricted then there's no hope of ever getting the rest right.  So give it a shot.  good luck and cheers,

Okay, if I'm understanding you correctly I could just disconnect the fuel return hose at the hard line (as per the fuel flow test), initially, and then check control pressure.

Obviously if that didn't produce any changes in the readings, I would then do as you suggest and eliminate the possibility of any blockage coming before the hard line by repeating the test via a hose connected directly at the FD?

I'd be potentially saving myself some hassle that way.  :D
'77 280se

raueda1

Quote from: SteveDuNord on 21 June 2023, 10:35 AM
Quote from: raueda1 on 21 June 2023, 06:51 AMExactly.  If fuel return in blocked or restricted too much then [system pressure] = [control pressure].  So check this first before going down the WUR rabbit hole.  Blowing compressed air through the return is just one way. You can try just blowing through the return tube but that's very hard to do and you need to blow out the fuel in the line before hearing bubbles in the tank.

Here's another way:  disconnect the fuel return line from FD.  Hook up a tube out of the FD into a container, similar to the fuel flow test.  Run fuel pump and check pressures. If the fuel return is blocked AND the WUR is actually OK then your control pressure should now be ok cause you removed the cause of the back pressure against the system.  Hope that makes sense.  There's no guarentee that this will solve the problem, but it's easy.  And if fuel return is constricted then there's no hope of ever getting the rest right.  So give it a shot.  good luck and cheers,

Okay, if I'm understanding you correctly I could just disconnect the fuel return hose at the hard line (as per the fuel flow test), initially, and then check control pressure.

Obviously if that didn't produce any changes in the readings, I would then do as you suggest and eliminate the possibility of any blockage coming before the hard line by repeating the test via a hose connected directly at the FD?

I'd be potentially saving myself some hassle that way.  :D
That's it.  Makes sense to me but I've struggled with this stuff too.  Others may have further comments.   
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

SteveDuNord

#107
Quote from: raueda1 on 21 June 2023, 11:30 AM
Quote from: SteveDuNord on 21 June 2023, 10:35 AM
Quote from: raueda1 on 21 June 2023, 06:51 AMOkay, if I'm understanding you correctly I could just disconnect the fuel return hose at the hard line (as per the fuel flow test), initially, and then check control pressure.

Obviously if that didn't produce any changes in the readings, I would then do as you suggest and eliminate the possibility of any blockage coming before the hard line by repeating the test via a hose connected directly at the FD?

I'd be potentially saving myself some hassle that way.  :D
That's it.  Makes sense to me but I've struggled with this stuff too.  Others may have further comments.   

Well I performed the CP test with the return line disconnected and it made no difference. Before repeating the test with a pipe attached directly to the return line union at the FD, I will move on to the next potential culprit.

There is a hard line leading directly to the WUR from the FD, is it worth cracking that with a spanner to see if there's a drop in CP?

Which reminds me: given that the WUR is unplugged for cold CP tests, am I right in assuming that it acts as nothing more than a conduit for the flow of fuel? That being the case, we are only really testing for a flow restriction at the WUR (mesh screen or hard line blocked), correct?

I've also read that inspecting the fuel pressure regulator at the FD is advised. But where is it? Well I'm guessing it's the flat nut on the left of this image, with the 4mm allen key in the centre?



I couldn't get the nut or the allen key to budge, so am leaving that alone for now.

The fitting to the right of the PR goes back to the WUR, I cracked it until fuel started to weep but the CP did not change.
'77 280se

SteveDuNord

Managed to crack the pressure regulator nut. The SP/CP did change as I loosened it, but nothing drastic, and the CP didn't drop independent of the SP. So all things point to the WUR.

The unit came out in two pieces. The sleeve design is correct for the model year. I've ordered an O ring kit to (hopefully) replace the existing ones. They look good, but it can't do any harm.





I'm not sure yet whether to attempt rebuilding the WUR with a kit, or send it off for reconditioning.

'77 280se

raueda1

That's the primary pressure regulator.  By all means, rebuild it, it's just replacing all the o-rings.  I posted a diasssembly process about it.  Read this.  Your WUR may indeed be bad, but if this thing is bad you'll never know.  And it DOES go bad, the o-rings go flat or tear etc.  O-rings are cheap.  So don't send out the WUR quite yet.  Do this first and you may not have to.  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

SteveDuNord

#110
Quote from: raueda1 on 24 June 2023, 06:53 PMThat's the primary pressure regulator.  By all means, rebuild it, it's just replacing all the o-rings.  I posted a diasssembly process about it.  Read this.  Your WUR may indeed be bad, but if this thing is bad you'll never know.  And it DOES go bad, the o-rings go flat or tear etc.  O-rings are cheap.  So don't send out the WUR quite yet.  Do this first and you may not have to.  Cheers,

Well I've managed to change the O rings but the slight issue of the world's tiniest c clip is causing an issue. How to heck do I pull the spring back with one hand, and pop that clip back on with the other?  :-\

Didn't start well. I almost destroyed the nut trying to get the torx bolt undone. Bit of penetrating fluid sorted that out.



Pulling back the silver cap on the spring reveals the tiny c clip. Remove it to dismantle the unit and reveal the 3rd hidden O ring.



Here's the clip on my fat finger. Have lost it several times trying to pop it back on. Even needle nose pliers aren't helping.



Edit: Managed to get it on, let's see if it changes anything!
The big O ring was a tad too large, so I replaced it with the next smallest one available and it seems to work fine.

Edit: nope made no difference to control pressure. Another possibility crossed off though!
'77 280se

SteveDuNord

#111
Well I managed to split apart the WUR and fit all new gaskets, etc, with a rebuild kit.

Two blade method.  ;D



A good few blasts of brake cleaner through the mesh filters this time around and they're looking a lot cleaner.

Fitted her back up this morning. Problem:
I didn't have the main WUR vacuum hose (the large one on the front/top) connected when I first started her over. This caused the starter to run on after turning off ignition.

Once reconnected and engine started: revs seem to be lower than normal and the gauge is holding only 3 bar system pressure. If you rev the engine, it dies, if you close the valve to check control pressure, the dial drops to zero and the engine dies.

I'm pretty sure everything is connected properly, and there are no fuel leaks, so either:

  • something has gone wrong with the WUR rebuild
  • The fuel pressure regulator rebuild (I don't think so)
  • I need to reset the mixture screw, which could have been set wrong while compensating for other problems.

Thoughts?

Update:
 Subsequent attempts to get her running have resulted in maximum system pressure on the gauge: this can be controlled by slowly closing the pressure test kit valve, but if you totally close the valve it rockets to the bottom of the gauge and stalls the engine. So - SP over 6bar, CP zero!

I leaned out the mixture screw which seemed to raise the revs but had no effect on the SP. I noticed it was taking way too many turns to reach that point where the mixture is too lean, almost stalling, which indicates to me that maybe we were running a tad rich.

But none of this has sorted the problem. I don't think it's the pressure regulator because I tested it before refurbing the WUR and it was holding normal SP.
'77 280se

SteveDuNord

Update, if only to keep a record.

I removed the FPR and it looked fine to me.

Popped it back in and had the brainwave to jump the pump: SP back to normal but CP still a fat zero on the dial.

Turned the engine over and the high SP was back. A puff of smoke led me to noticing oil on the manifold. I guess super high system pressures can cause a gasket to blow!







In a year of (expensive) ownership, I've driven maybe ten miles.  ;D
'77 280se

rumb

Fluid at exhaust manifold joint could be valve stem seals and/or guides. Does it smell like gas? That could be from attempting to start a lot of times.

My MG looked like that and head rebuild fixed.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

SteveDuNord

I'll have to worry about that later.

For now, system pressure is through the roof and I can only assume that's why the manifold is leaking.

System pressure normal if I only jump the pump. Baffled and can't find anything online.
'77 280se

rumb

You might try reaching out to H.D. over at Benzworld.  He seem to be quite knowledgeable.

https://www.benzworld.org/threads/ke-jetronic-cis-e-info-advice.3065993/


Have you followed the diagnostic process completely?  Fortunately I have never had the need, but it appears quite logical and thorough.  step 9.3 caught my eye.  Have you checked for vacuum at the WUR?

https://cdn.w116.org/tech/K-Jet_Diagnosis_Adjustment.pdf
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

ramiro

If i understand it right you are affecting the system pressure by closing the valve to the wur?
That makes no sense whatsoever because the system is regulated internaly in the fuel distributor , i think you are just seeing 0 bar control pressure when the valve is open and 6 bar system pressure when it's closed.

If you really have 0 bar control pressure it's no wonder your exhaust is leaking because your engine
is running super rich and is pushing tons of unburned fuel into the exhaust.

For me it seems that the system pressure regulator is not working anymore and also the wur.
You cannot open the wur change the seals and put it back on the car without completly readjusting it , just opening it and closing it will change the adjustment.

raueda1

Yeah, something is very wrong here.  When rebuilding the And WUR did you polish the surface on the cylindrical valve body?  And doing the same on the housing certainly doesn't hurt.  At this point my bandwidth has kind of been consumed on this problem so I return to my K-Jet creed:  "Unless everything works, nothing works."  So, maybe time to take a step back, reboot and start over as Robert suggests.  The CIS manual (on this site someplace) is your best friend.  If I were you I'd go back to that, start at the beginning and proceed step-by-step without skipping anything or jumping around. Not skipping is a key point even if you think "I've already done that." Also, as ramiro says,  you'll absolutely be recalibrating the WUR at some point.  I'd therefore strictly avoid running the engine until you get it nailed down better (don't ask me how I know this). Keep at it, eventually you'll crack it.  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Feather535

It has taken me a while to read through this thread, but having gotten to this point I agree that something has gone wrong in your process.  Control pressure should be about 1 bar cold and 3.8 warm, so a CP of 0 would make for a very rich mixture. 

Since you have disassembled the WUR and installed new parts, you also need to recalibrate it.  Guides are available in various places, for example:  https://k-jet.biz/wp-content/uploads/2019/06/Basic-WUR-Set-Up.pdf.  And did I understand correctly that you removed the fine mesh screens inside the WUR?  I've been told that those help to set the base pressure for the WUR, so their absence could explain your low CP. 

As others have said, it's important to go step by step, but until you fix the mixture problem, any further testing should be done with only the fuel pump running, and not the engine.
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

SteveDuNord

Well, I've finally found the time to start up my WUR odyssey again.
Reading through the guides, a proper adjustment procedure involves setting three different WUR components.
1) the bimetallic strip pin
2) the fuel cell
3) the stud on the rear of the WUR (bottom plug)

Every DIY effort I've researched seems to ignore the bottom plug.

First let's smack 1) until it is level with the casing. Stick the nut on so as not to damage the thread and whack it several times with some force. I rested the case on a big hammer.



This should leave the pin flush with the casing



Next the fuel cell 2)

Remove the fuel inlet/return nuts and place a socket on the cell, smack it until it comes out the other side. Don't disturb the hole it rested in or you'll risk creating a vacuum leak!



Finally we have the bottom plug. This is where it gets interesting...



This plug should be knocked out, then pushed back in gradually during the pressure set procedure. But in order to get to the plug you have to prise apart the lower diaphragm casing, which might require you having to replace the gasket/diaphragm thingy underneath - I just replaced mine so am reluctant to proceed.

However... some say that the plug is just there to stop you tampering with the Allen key bolt that lies beneath it! And that you can drill a hole through the plug to access the Allen key bolt... IF that's the case, and you can get the same results turning the bolt as gradually tapping the plug back in... then why not just drill?

Here's a fuzzy screenshot of the only source I could find for this info:




If anybody has any info on this method, I'm all ears!
'77 280se