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High control pressure

Started by Feather535, 12 November 2022, 09:06 PM

Feather535

In the continuing saga of my rescue 280SE, testing fuel pressure has revealed some interesting things.  Primary system pressure is right where it should be at 5.2 bar.  But when I open the valve, the pressure drops at first, then quickly comes back to 5.2 bar and stays there.  It's the same cold or hot. 

So why does the pressure stay high?  Seems like there could be an internal restriction in the WUR (aka control pressure regulator)?  Or in the return circuit from the WUR to the tank? 

The static (residual) pressure test with the fuel pump off initially shows 2.5 bar, but it drops to 0 after an hour, so something must be leaking.  It's not the cold start valve, so the accumulator is the prime suspect.  It's old and should probably be changed regardless.  Make sense?


raueda1

Quote from: Feather535 on 12 November 2022, 09:06 PMIn the continuing saga of my rescue 280SE, testing fuel pressure has revealed some interesting things.  Primary system pressure is right where it should be at 5.2 bar.  But when I open the valve, the pressure drops at first, then quickly comes back to 5.2 bar and stays there.  It's the same cold or hot. 

So why does the pressure stay high?  Seems like there could be an internal restriction in the WUR (aka control pressure regulator)?  Or in the return circuit from the WUR to the tank? 

The static (residual) pressure test with the fuel pump off initially shows 2.5 bar, but it drops to 0 after an hour, so something must be leaking.  It's not the cold start valve, so the accumulator is the prime suspect.  It's old and should probably be changed regardless.  Make sense?


Most of these issues have multiple potential causes and have been repeatedly covered.  Your best friend is the CIS adjustment & diagnosis manual in the technical section.  Start at the beginning and work through.  In the course of that check the filter on the fuel line on the FD and the filter in the WUR.  Look for fuel line restrictions too.  Do a search for more details.

As for static pressure, there are many more potential causes than bad accumulator.  But as I recall the spec is only 30 minutes anyway, so there may not be a problem at all. See manual for specifics.  And look at my recent thread on rebuilding the pressure regulator valve.  Just remember, you need to go through in sequence, not jumping around.  Hope this helps you get started.  Cheers,


This: Try this:

And this:
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Feather535

Thanks.  I am using the factory manual and the Bentley Bosch Fuel Injection book and going step by step.  There are multiple interconnected issues, as you say.  The most pressing one right now is cold starting.  The mixture is too lean cold: the cold start injector doesn't work at all, the thermo-time switch tests bad, AND the cold control pressure is too high.

That said, your thread about equal ontrol and system pressures is helpful.  Where you said "The problem turned out to be the pressure regulator assembly" which regulator are you talking about?  The one in the fuel distributor?

Another question: is CIS Flowtech still in business? Google doesn't find a website for them.

raueda1

Sounds like you're headed in the right direction.  ;D   A few comments....

Regarding manuals, the bible here is the MB CIS Adjustment and Diagnosis Manual on the site's technical page. You need to do what it says in the order that it says it. I'd be very cautious using the Bentley manual without knowing more.  K-jetronic was used in zillions of cars and there were countless small variations.  The same era Porsches and MBs differed in small ways and details for example, full load enrichment and warm-up configurations are different, etc. 

I don't know if these cars will start at all if cold injector is kaput, but obviously that needs to be fixed.  The A&D Manual is very explicit about troubleshooting.  That said, my car's cold control pressure is too high (lean) at the moment, about 2 bar at 10C.  It should be more like 1 bar at that temp.  Still, the car starts right up. 

Yeah, restrictions can make you nuts - fuel return, fuel supply filter on FD, filter on WUR input, etc.  It's worth noting that blowing compressed air through the fuel return line does not necessarily mean the line is clear. The rubber parts can be swollen or partially blocked enough to mess up the system pressure but still pass air under enough pressure.

As for static pressure, the spec is 2.5 bar after 30 minutes.  How fast it drops after that I don't know, but 0 bar in an hour doesn't necessarily indicate a problem.  So check after 30 minutes.

Yes, the regulator I speak of is the primary system pressure regulator on the side of the FD.  If in doubt just rebuild it.  All it takes is 3 o-rings.  It might help, as it did for me, or not.  If no then it isn't a problem and you can look elsewhere.

Keep posting and keep searching the forum.  Zillions of us have have similar or identical issues.  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Feather535

The person I bought this car from had installed a new fuel pump and filter, but it wasn't drivable until I corrected the ignition timing, fixed some vacuum leaks and changed the little screen in the FD inlet.  It can be driven now, but too lean on cold starts and seems down on power even when warm.  I didn't know there was a filter in the WUR, but will check that and the return line.       

Quote from: raueda1 on 13 November 2022, 07:16 PMI don't know if these cars will start at all if cold injector is kaput, but obviously that needs to be fixed. 

So where to get a cold start injector?  So far I've only found them on eBay-a bit dicey IMHO.

ProfessorExperimental

Obviously these guys are in Australia but:
https://www.fuelinjectionparts.com.au/bosch-0280170412-start-valve-280170412.html

I just pulled the Bosch part number for the injector from one of the eBay listings you mentioned: your local Bosch service should be able to confirm if that's the correct part for your car and then you can order it through them or your preferred local parts supplier. ofc it should also be stamped on the injector, on one side of the plug (probably the side facing down with the injector installed, Murphy's Law and all that...)
-Mark

raueda1

Quote from: Feather535 on 13 November 2022, 10:44 PMThe person I bought this car from had installed a new fuel pump and filter, but it wasn't drivable until I corrected the ignition timing, fixed some vacuum leaks and changed the little screen in the FD inlet.  It can be driven now, but too lean on cold starts and seems down on power even when warm.  I didn't know there was a filter in the WUR, but will check that and the return line.       

Quote from: raueda1 on 13 November 2022, 07:16 PMI don't know if these cars will start at all if cold injector is kaput, but obviously that needs to be fixed.

So where to get a cold start injector?  So far I've only found them on eBay-a bit dicey IMHO.

Try emailing the Classic Center with year model and VIN.  They'll get back to you very fast.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

I found 0280170403 listed for 280se.

https://www.ebay.com/itm/401758881226

I suspect used is all you will find.

CIS Flowtech - looks like the webpage is down.  http://www.cisflowtech.com/  (251) 929-3771

I called and left message on machine. Hopefully it's that they are over busy and just not taking care of things?


'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS

raueda1

Quote from: Feather535 on 13 November 2022, 12:26 PMThanks.  I am using the factory manual and the Bentley Bosch Fuel Injection book and going step by step.  There are multiple interconnected issues, as you say.  The most pressing one right now is cold starting.  The mixture is too lean cold: the cold start injector doesn't work at all, the thermo-time switch tests bad, AND the cold control pressure is too high.
>>>snip<<<
It just occurred to me that Part 6 of the CIS troubleshooting manual ("testing cold start valve system"), is lacking page 25.  My system works OK so I never missed it.  But it raises the question, can you be sure that the cold start valve is NG if the thermo-time switch is NG?  Does the Bentley manual have an equivalent to page 25?  No sense in looking for a new valve if the problem is the switch.  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 14 November 2022, 07:08 PMIt just occurred to me that Part 6 of the CIS troubleshooting manual ("testing cold start valve system"), is lacking page 25.  My system works OK so I never missed it.  But it raises the question, can you be sure that the cold start valve is NG if the thermo-time switch is NG?  Does the Bentley manual have an equivalent to page 25? 

I noticed that, but the last thing on p. 24 is "DISCONNECT plug on thermo-time switch," which sounds like the test is done without the switch in the system.  The Bentley manual says to jumper the cold start injector from the coil.  I haven't done that yet, so maybe it's not time to condemn the injector yet. 

revilla

#10
This IS NOT in the « book » but this is how I test CSV's the  un-orthodox way to be 100% positive they work, or not, with zero tolerance for doubt.

1) take it out its mounting place (2 allen type screws + fuel line)
2) connect 12V, you hear clicking? If yes, good sign, but not enough for me
3) turn the fuel line so it points upwards (rather than downward for normal installation).
4) reconnect the CSV so the nozzle points out to the exterior.
5) pressurize the system, but without starting the engine, obviously.
6) give it another 12V pulse using a rag around it to prevent spilling. Do you see fuel spraying? If no, you have your answer.
7) repeat the above procedure but with the blue connector attached to the CSV in order to test the functionality of the TTS but this time using the car's ignition, just a pulse without starting the engine (disconnect coil to distributor cable, both ends.

If done correctly it's the best way you can be absolutely certain they work properly, or not. Needless to say, do not attempt to start the engine with the CSV disconnected and use all precautions for fuel spilling and fire hazards.
The test can be done in a bench setup if you have what it's needed. The test above is the poor man pragmatic option but be careful please.

Report back results or questions you might have.
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100][url="http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG"]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/url][/img]

Feather535

So I tested the cold start valve again using basically the procedure revilla and the Bentley fuel injection manual describe. I removed the valve from the manifold, left the fuel line attached, and connected one terminal to ground and the other side to 12V while operating the fuel pump.  The injector does spray fuel when the pump operates, so it must be ok. The resistances of the thermo-time switch are also in spec. 

From these tests, I think this car's lean condition when cold isn't due to the cold start valve. If you've read the whole thread, it looks like high cold control pressure is the next thing to address.

revilla

Hi,

The purpose of the test procedure described was double. I thought it was obvious, but maybe not. My bad. It was to check the CSV sprays when pressure and 12V are applied, but ALSO very important to check it doesn't leak when pressure present but no power.  Essentially you want to check it opens and closes without leaking with and without 12V power applied. I didn't get that confirmation from your description. A leaking CSV is common and can be a real problem.  Also for the TTS, assuming it's ok because the "book" resistance values check ok is a big risk. Let's be pragmatic about it and let your test tell you if the TTS commands the CSV to open (spray) and closes (with zero leaking) after about 8 seconds. Can you confirm that before moving ahead with the "book" approach? I haven't read the whole thread. How do we know it has high CP when cold? What bars values are you reading? 2bars? 3bars? Does it go higher (leaner) when passing from cold to warm (generally about 3-4 minutes of operation)? If so, to what value? 3.4? 3.8? 4.0?
These are the figures that we need to help you. They are the ones "telling"us the story and thus the next actions to improve the current situation. Put the "book" aside for a minute and let's try to understand, with data, the actual conditions to determine the next steps.
Good luck.
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100][url="http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG"]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/url][/img]

Feather535

Quote from: revilla on 15 November 2022, 11:34 PMLet's be pragmatic about it and let your test tell you if the TTS commands the CSV to open (spray) and closes (with zero leaking) after about 8 seconds. Can you confirm that before moving ahead with the "book" approach? I haven't read the whole thread. How do we know it has high CP when cold? What bars values are you reading? 2bars? 3bars? Does it go higher (leaner) when passing from cold to warm (generally about 3-4 minutes of operation)? If so, to what value? 3.4? 3.8? 4.0?

The cold start valve doesn't leak; I tested that. I do want to retest the CSV in combination with the TTS, because the first results of that test weren't consistent.

The cold control pressure is the same as the system pressure, about 5.2 bar.  So is the warm control pressure.  So I think now that the lean running issue is likely to be related to the WUR or the return circuit.  Suggestions appreciated, as always.


raueda1

Quote from: Feather535 on 17 November 2022, 10:51 PM
Quote from: revilla on 15 November 2022, 11:34 PMLet's be pragmatic about it and let your test tell you if the TTS commands the CSV to open (spray) and closes (with zero leaking) after about 8 seconds. Can you confirm that before moving ahead with the "book" approach? I haven't read the whole thread. How do we know it has high CP when cold? What bars values are you reading? 2bars? 3bars? Does it go higher (leaner) when passing from cold to warm (generally about 3-4 minutes of operation)? If so, to what value? 3.4? 3.8? 4.0?

The cold start valve doesn't leak; I tested that. I do want to retest the CSV in combination with the TTS, because the first results of that test weren't consistent.

The cold control pressure is the same as the system pressure, about 5.2 bar.  So is the warm control pressure.  So I think now that the lean running issue is likely to be related to the WUR or the return circuit.  Suggestions appreciated, as always.

I've had recurring problems with similar stuff.  The causes are always different but symptoms often kind of cluster together.  These cars are old.  When we fix one thing but we rarely fix everything.  So then 6 months later another filter clogs or o-ring fails.  Then that problem gets chased down.   This is the story of my life.   After a few years everything ends up renewed! Anyway, check out this thread if you haven't already.  Very similar (or identical) problem.

https://forum.w116.org/mechanicals/wur-return-blockage-in-fuel-distributor/msg138453/#quickreply_anchor

And more recently there's this:

https://forum.w116.org/mechanicals/primary-fuel-pressure-regulator-is-disassembly-possible/15/


-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0