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C w202 250TD - Air In Fuel system

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by itchey, Aug 19, 2012.

  1. itchey

    itchey Active Member

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    Your Mercedes:
    1999 Mercedes 250TD Sport Auto.
    Could someone out there advise me on my thoughts of why air is getting in the fuel system.
    For about 6 months now I never know if the car is going to start up first time in the morning, espcially if I haven't driven it for a couple of day. It is intermitant and can go days without any trouble then out of the blue it decides not to start and I have to churn the engine over ( Buggering up the starter motor) for about 20 seconds or so to get fuel through. Once it is started it will stop and start perfectly all day untill I leave it to stand overnight. I have spent a small fortune replacing every pipe and O ring and so far 3 garages have failed to cure it or find anything in the diagnostic.
    I noticed that the problem seemed to happen when the tank was about 1/4 full but now it seems to happen when the tank is between 3/4 and 1/2 full. (Coincidence??)
    What realy puzzles me is why the fuel pipes and filter are full of air. It's as if the fuel is being drained back into the tank. There are no fuel leaks and I would imagine if there was an air leak it would show itself when driving not when standing.
    Is it possible that a vaccuum is being caused in the tank and so sucking everything back, or am I on the wrong tack? I did think of putting a none-return valve in the supply line but the latest garage told me it would upset the sensors. (Poor things!) I've run out of ideas so any fresh thoughts would be appreciated.
    Thanks,
    John
     
  2. eihtur

    eihtur Senior Member

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    Your Mercedes:
    Mercedes C180k 3door
    Hardening of the plastic fuel pipes and O rings will do this.
     
  3. spock500

    spock500 Senior Member

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    Your Mercedes:
    300TD, 1998
    Fuel will syphon back into the tank pulling air into the system at the same time, you not see diesel leaking.

    If you have checked pre-filter along with the clear pipes and O rings then it's most likely the delivery valve seals.

    These rely on a 'hydraulic lock' being maintained between the valve seat and the injector nozzle.

    Miles and age are both contributing factors as there are two types of seal, one is copper the other rubber.

    Check out the stickies.
     
  4. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    Your Mercedes:
    C220CDI AMG Line Premium, SLR McLaren Roadster, SL55 & C32AMG
    There is also a plastic 1 way valve on the side of the pump that either leaks or stops working. I had to do mine last week.
     
  5. OP
    itchey

    itchey Active Member

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    Your Mercedes:
    1999 Mercedes 250TD Sport Auto.
    Thanks guys,
    I will have to get everything checked out. (There seem to be so many things it could be, it makes me long for the good old days when I could see everything and fix things when they went wrong, which they frequently did.)
    In any event, if it is the hydrolic lock does anyone know if it is sucked back to the tank through the delivery line or the return line?
    Thanks again,
    John
     
  6. spock500

    spock500 Senior Member

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    Your Mercedes:
    300TD, 1998
    It's probably a bit of both as the return forms part of the delivery loop.

    The fuel is drawn from the tank via the lift pump (32) into the pre-filter then the first stop solenoid. From the stop solenoid (74) it is then pushed into the main filter - at this point a pressurised loop is formed with the return (see double arrow pipe 146) - on leaving the main filter it is then pushed into the second stop solenoid before the delivery chamber. This part is low pressure but balanced with the return/leak off pipes.

    From this reservoir of low pressure fuel the delivery valves draw their supply, these are cam driven forming the high pressure part of the final delivery to the nozzle.

    Sorry, if it's a bit vague but haven't tinkered with the oily bits in a while.


    [​IMG]
     
  7. OP
    itchey

    itchey Active Member

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    Your Mercedes:
    1999 Mercedes 250TD Sport Auto.
    Thanks

    Thanks David. That is the first diagram that I've come across that I can understand. It happened again yesterday afternoon. It is the first time it has happened during the day. It start and ran perfectly in the morning but decided to throw its hand in after standing for about 8 hours. This morning it started on the button. WHY???? If air is being drawn into the system I would think it would happen all the time. It's a bugger. If I put it into a garage it might be days before it happens again. I wonder if it could be identified on a diagnostic test. I have had them done before (No joy) but not on a Star which is difficult to find in my area. I have been told that the Snap-on system is just as good. Has anyone any experience of it.
    Thanks again to all you guys out there.
    John
     
  8. yorkshire1

    yorkshire1 Senior Member

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    Your Mercedes:
    "98 S202 C250TD Manual hybrid
    sensors

    dont know what sensors would be upset as there arent any to upset put 1 way valve on and whilst youre at it put siome clear tubing on the suction side from the metal feed pipe on the inner wing then with the car running youll see whether there is air coming into the system from the tank and/or pipework these cars can and will get air in anywhere, clear tubing helps and just follow the bubbles through, prefilter housing can also go porous
     
  9. yorkshire1

    yorkshire1 Senior Member

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    Your Mercedes:
    "98 S202 C250TD Manual hybrid
    valve

    Steve, what is the black valve on the side of the pump for, its always wrongly referred to as the stop solenoid but noone has yet been able to say what it does even Merc dealer
     
  10. spock500

    spock500 Senior Member

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    Your Mercedes:
    300TD, 1998
    It's the stop solenoid/shut off valve.

    [​IMG]
     
    Last edited: Aug 23, 2012
  11. spock500

    spock500 Senior Member

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    300TD, 1998
    John, I think we need to step through this as it's an easy fix provided we follow a logical path.

    Firstly, who replaced the O rings and did they replace the pipes too?

    If so, have all of the pipes and O rings been replaced as listed in the diagram above?

    Has the main fuel filter been replaced along with the smaller pre-filter and O ring, part 26?

    When changing the main filter were the two O rings replaced on the bolt?

    The stop solenoid above has O rings although I am not sure they would cause the symptoms you report - worth doing anyway though.

    Lastly, how many miles has are on the clock?

    The more detail you can provide the better chance we have of advising you.
     
  12. yorkshire1

    yorkshire1 Senior Member

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    Your Mercedes:
    "98 S202 C250TD Manual hybrid
    no

    sorry but that isnt a/the stop solenoid, thats the misconception, inline pumps stop by moving the rack internally which cuts fuel delivery to the injectors steve @aventgarde has referred to "one way valve" in his post which is nearer the mark but what its function is is the mystery
     
  13. spock500

    spock500 Senior Member

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    That's incorrect, the rack is static - what made you think it moved in this manner?

    Please see part number 29 on the link below.

    http://mb.ilcats.ru/part/class/1/ccode/1/cat/19S/type/605/subtype/910/group/07//

    Seal replacement

    http://www.benzworld.org/forums/w202-c-class/1542820-c250-diesel-shut-off-valve-leak.html
     
  14. spock500

    spock500 Senior Member

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    Your Mercedes:
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    Cross section of the stop solenoid although it's referred to here as 'Electrohyraulic shutoff actuator'.


    [​IMG]
     
  15. yorkshire1

    yorkshire1 Senior Member

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    Your Mercedes:
    "98 S202 C250TD Manual hybrid
    no

    beg to differ, rack is actuated by fly by wire throttle electronics inside back of pump body which moves rack laterally to turn delivery valves which in turn lets more or less fuel through to the injectors and its this movement of the rack that shuts off the fuel stopping the engine once ignition is turned off, that black valve couldnt stop the engine dead as the plungers in the pump would still be able to force fuel up to the injectors because the gallery would have fuel in it still and the engine would only gradually come to a halt
     
  16. yorkshire1

    yorkshire1 Senior Member

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    Your Mercedes:
    "98 S202 C250TD Manual hybrid
    link

    hhttp://transportation.centennialcollege.ca/oduffy/fuels/HD%20fuels%203/inline.pdf
    transportation.centennialcollege.ca

    hope link works
     
  17. spock500

    spock500 Senior Member

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    Your Mercedes:
    300TD, 1998
    I have shown two Mercedes diagrams one clearly identifying the part as the 'shut-off valve, the other 'Electrohyraulic shutoff actuator', together with a description of it's operation.

    On the OM605 (non turbo) there are no electronics connected to the pump at all, only the wires leading into this valve via a plug - the rack cannot physically move as there is a cam shaft underneath preventing this so how did the engine stop?

    This is not a very good picture but the side plate has been removed to change the seal, this shows the valve gallery in situ.

    [​IMG]

    On later models they added electronics which did indeed alter the mixture, but they still retained the stop solenoid.

    I popped down to double check my engine which is one of the later models fitted with an electronic actuator. The solenoid as described above is still present.

    It sounds odd that you have encountered a Mercedes dealer which doesn't know what a part is for? They have the EPC in front of them which details pretty much everything you need to know, failing that they can always refer to WIS for further info.

    I guess we are getting a little o/t, apologies.
     
  18. OP
    itchey

    itchey Active Member

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    Your Mercedes:
    1999 Mercedes 250TD Sport Auto.
    Thanks again guys

    Thanks very much everyone.

    In answer to your questions David, all the clear pipes and O rings going to and from the filter were replaced with the Mercedes kit. They were replaced by the local mechanic and it made no difference.

    The O ring on the clear pipe to the top of the pre-filter was replaced with the kit but the pre-filter itself wasn't changed.

    The fuel filter was changed twice but I don't know about the 2 O rings on the holding bolt. I presume these would come with the filter.

    The stop solenoid O rings have not been replaced.

    The heat exchanger has been replaced.

    The car has done 140,000 mls.

    I started the car this morning without any problems and after letting it tick over for a while I stopped it. I watched as fuel drained back very slowly through the clear delivery pipe leading to the pre-filter housing, dragging a plug of air with it. I left it for half an hour then looked again. The fuel was lower down in the pipe again. I couldn't see any air bubbles coming up to the filter from any of the other clear pipes.

    I am definately thinking of the inline none-return valve and even giving the filter housing a thick coat of metal paint just to try to eliminate a couple of things before throwing it to the mercy of another garage.

    All the things that have been replaced have made no difference so I presume that they were not the problem but I hope this is a clearer picture.
    My best to everyone,
    John
     
  19. spock500

    spock500 Senior Member

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    Your Mercedes:
    300TD, 1998
    Ok, there's a couple of easy things to do if you have a 10mm socket.

    Pop out to the car and undo bolt no. 50 on the above diagram. With a flat blade screw driver gentle lever out the pre-filter - it should be clear with no sediment in the bottom.

    Second, unscrew your fuel cap before starting, it could be the fuel tank breather is blocked causing a vacuum in the tank - Put a note on the dash to remind re-fitting of cap.

    This way we can narrow it down a tad, good luck.
     
  20. hawkspeed

    hawkspeed New Member

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    air in fuel lines.

    Had the same problems tried everything in the end fitted new lift pump off ebay for about £100 that was 3 yrs ago never any more problems runs sweet.
     

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