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Cummins 4B3.9-G2 Losing Fuel Prime

Discussion in 'Generators/Gensets' started by Jacques van Heerden, Aug 23, 2018.

  1. Jacques van Heerden

    Jacques van Heerden New Member

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    Location:
    China
    I have 45 x 15KW Cummins(4B3.9-G2) Gensets to power emergency sirens on a 40km gas pipe line in case of a leak that I do maintenance on. The units have remote GPS start signals to start the generators in an emergency. We do testing every 2 weeks. Tests are done to function test and we run for an hour to charge batteries. Every 2 weeks there is at least 10 or more generators that won't start and have to be manually primed before they start. The engines are equipped manual plunger prime pumps (I see Cummins calls them Fuel transfer pumps and is driven by the engine once running). We have good quality low cracking pressure non-return valve on the inlet fuel hoses and it appears that there is actually fuel in the hose (semi see through) yet some times they have to be manually pumped up before they will start. I need these engine to run first time every time once a start signal is given... where do I start to check the priming issue? I've seen an article saying that the injection pump might loose its prime via the fuel return line when stationary. Is that possible? how to I fix it. Thanks, J.
     
  2. thepumpguysc

    thepumpguysc Senior Member

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    Occupation:
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    Where is YOUR non return valve located on the inlet? IF its up close to the inj. pump INLET.. move it back to the "fuel transfer pump" OUTLET..
    THAT WAY, you will have more fuel in the line for the pump to run/start on..
    TRY IT, I'll bet it works.
    A few other ideas..
    How about the electric shut off?? Have someone check to MAKE SURE the electric shut off solenoid on the inj. pump IS ACTUALLY ENERGIZING, when the signal is given to start.. The only way to do that is w/ a volt meter AT the inj. pump. & whats the voltage?? You need AT LEAST 10volts to energize the solenoid.{on a 12v system}
    IN THEORY a leaking non return valve in the return circuit/on the inj. pump return, will cause air in the system.. BUT, I have 30 years OF FIELD EXPERIENCE & have NEVER seen it happen.. THATS what I used to do, go out in the field & solve problems such as this..
    Another thing> is the fuel transfer pump itself.. it could have leaking valves in it, allowing the fuel to drain/siphon back to the fuel tank..
    That's where YOUR non-return valve comes into play.. IF you move it back to the trans. pump OUTLET, it will be harder for the fuel to siphon back.. also, the added fuel in the line from the trans. pump TO the inj. pump will be greater, allowing for extended run time before the transfer pump can pick-up the fuel from the fuel tank..
    Good luck & send a check to The Pump Guys SC.. Lol
     
  3. funwithfuel

    funwithfuel Senior Member

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    Pumpguy is the authority on this stuff, but you want to look for air intrusion. Primary candidate for me would be overflow valve and injector return lines.

    I see I got treed
     
  4. thepumpguysc

    thepumpguysc Senior Member

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    One more thing>> you COULD disable the Cummins transfer pump & install an electric transfer pump in its place.. guaranteeing fuel at the inj. pump inlet..
    Its a LOW pressure unit so a LOW pressure pump will be required OR you'll blow the seals out of the inj. pump.. 5-7 psi MAXIMUM.
    I'm assuming this is a Delphi/CAV rotary injection pump??
     
    Delmer likes this.
  5. thepumpguysc

    thepumpguysc Senior Member

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    IF this happens to be a BOSCH INLINE pump.. YES, the overflow valve would be the 2nd thing & would check.. The first would be inj. pump inlet pressure.. testing the transfer pump pressure, to the inj. pump inlet.. The pressure should be NO LESS THAN 25 psi.
    BOTH are weak points in the starting circuit.
     
  6. Jacques van Heerden

    Jacques van Heerden New Member

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    Location:
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    Thanks for taking the time to respond.
    The pump is a BYC with Cummins part number 5290005 - I believe these are the Chinese equivalent of the Bosch pump. Maybe worth mentioning - these Cummins engines are DCEC (Dongfeng Cummins Engine Company) manufactured for Cummins under license. You might have seen these State side? I can still use the Cummins E.S.N number to search parts on QuickServe site. I wonder if the quality of the fuel transfer and injection pumps are not 100% what they are supposed to be and both have some sort of internal leakage issues.

    To get back to the non-return valve. At the moment they are installed at the fuel line inlet inside the tank. Sounds like that's not the best place to be?
     
  7. thepumpguysc

    thepumpguysc Senior Member

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    Ok, its a "A" pump w/ an electronic governor.. You'll have to take 1 or 2 units to "experiment" on..
    REPLACE the inj. pump non-return valve{overflow valve} & MOVE the ENGINES non-return valve on 1..
    & REPLACE the {overflow valve} inj. pump non-return valve & the lift pump on the other..
    & see which one starts faster..
    The pumps non-return valve{overflow valve} can be purchased from, a diesel fuel injection shop..
    Bosch part # 2 417 413 084