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Unimog 416 Starting

Discussion in 'Unimog Technical' started by Dawie Louw, Jul 9, 2017.

  1. Dawie Louw

    Dawie Louw G-Wagen Club SA

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    When starting my Mog from cold, it takes about ten tries before it actually starts up and idles. I am talking "normal" ambient temperature, certainly above 12 degrees ambient temperature, not around freezing point, start-up.

    I have tried priming, not priming. no throttle pressure, little pressure, lots of pressure, first with killer pulled, etc. It will crank, start and die, crank, start and die. After about eight to ten tries, it will sart, hesitate and then idle. Once it idled for a bit, it starts within a few starter turns. The injectors have been overhauled and has new tips. The compression is lowish but not really below spec.

    What may be the cause? Any suggestions to save my starter?

    ,
     
  2. Andrew

    Andrew Moderator G-Wagen Club SA

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    Non return valve leaking in the lift pump??
     
  3. Stu

    Stu Member

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    Try a temporary fuel tank mounted above the motor, will eliminate air leaks and pump problems......
     
  4. paulventer

    paulventer Active Member

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    A pin-hole leak in a fuel line can also cause this - leading to fuel draining back to the fuel tank when standing.

    Stu's suggestion is a very good idea.

    The mogs always amaze me at how well they start - at least at temps above 10 degrees. Mine normally starts within a second or two even after standing for a couple of weeks. And that without any form of glow plugs!

    At lower temps they are a bit problematic, especially the 12V versions. The 24V starter motors have more power and spins faster, which seems to help with cold starting.
     
  5. Dawie Louw

    Dawie Louw G-Wagen Club SA

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    I will try with a small gravity feed tank when I get a chance. I must first get a piece of suitable hose. I would have thought that priming with the primer pump there should be sufficient and airless fuel at the pump.

    Thanks for the promp suggestions.
     
  6. paulventer

    paulventer Active Member

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    The primer pumps sometimes develops a leak at the glass filter bowl and then suck in air. Check that the glass filter is seated properly and that the seal is still intact.

    The primer pumps themselves can also fail sometimes, although the fact that yours runs leads me to believes yours is still working.


    Sent from my iPhone using Tapatalk
     
  7. paulventer

    paulventer Active Member

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    Dawie

    Have you checked the fuel filters?

    I just remembered an incident I had several years ago. I did a week long trip to Sabie and the mog ran perfectly. Got home and parked the mog. Two week later when I then tried to start the mog it just wouldn't start. Engine would turn over and cough a few times, but wouldn't run at all. After a long search and lots of head scratching it turned out I had a bad batch of diesel with fungi in which glogged the fuel filters to such an extent that they wouldn't allow enough fuel through for the mog to start.
     

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