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Purge Air from Fuel Line - General Diesel Engine Help

Discussion in 'Compact Wheel Loaders' started by skobydog, Apr 14, 2018.

  1. skobydog

    skobydog Active Member

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    I was an idiot and ran my backhoe/FEL out of fuel the other day. I believe I now have air in the line preventing the machine from starting.

    I've come across a few videos online but I'm still not sure how to purge/bleed the line. Can someone explain how I should or can proceed to get the air out? From my limited understanding I believe I can use vacuum to pull fuel out through the return line. I have available a hand vacuum pump from a brake bleeder kit and also a 7 cfm A/C vacuum pump.

    From my understanding I may have to purge or bleed the fuel line at a few different locations. I've also seen guys loosen injectors to bleed air out.

    The machine is a 1986 New Holland LB-620. The engine is an Onan 4 cyl diesel.

    The first pic is obviously not my engine but similar.
    Second pic is Water Separator/filter?
    Third Fuel Filter
    Forth fuel injection pump?

    Any help would be appreciated. Thanks


    003.jpg

    vlcsnap-2018-04-14-05h36m38s37.png

    vlcsnap-2018-04-14-05h37m22s23.png

    001.jpg
     
  2. skobydog

    skobydog Active Member

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    Here are a couple other pics

    vlcsnap-2018-04-14-05h40m49s196.png

    002.jpg
     
  3. skobydog

    skobydog Active Member

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    I was able to find what I believe is the fuel lift pump. I was trying to find it using a parts catalog which is horrible. I was able to do a cross reference which shows the level on the pump. Sure enough it's under there but very hard to see.

    Now, I believe I'm supposed to bleed the water separator/fuel filter first by loosening the nut shown in the red circle. I'll have to review this a bit more for the next step. The final step I believe is loosening the injectors to let air out that way.

    004.jpg
     
  4. funwithfuel

    funwithfuel Senior Member

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    Do NOT LOOSEN THAT SCREW!
    That holds your slurry bowl top, and bottom together. If you don't have the seals for it, you'll most likely cause a leak. Just pump the lever, til the lever kinda falls away, wait a few then do it again. Now crack a line nut loose to an injector. Crank engine til fuel jets from loose line. Tighten line reasonably tight and start.
     
  5. skobydog

    skobydog Active Member

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    Thanks a lot. I won't loosen that screw. I'm not sure what you mean by the lever falling away but I guess I'll notice it when I try pumping it.

    I'm still waiting for my fuel filter to come in the mail before I go any further. I think it should be here Tues. Thanks
     
    Last edited: Apr 14, 2018
  6. kshansen

    kshansen Senior Member

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    Not familiar with this particular engine but if the fuel lift pump is one of those that works off a lobe on the camshaft if it does not seem to be doing anything try turning the engine over maybe half a turn or so and try again.

    Reason is if the engine stops with the pump plunger on the high side of the cam lobe the hand lever will not do anything, needs to be on low side of the cam lobe.

    Problem is there is no simple way to know this so it's more or less done by feel on the lever.
     
  7. Birken Vogt

    Birken Vogt Charter Member

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    This engine is an Onan L series, also known as a Cummins A series.

    It has a rotary Stanadyne pump which in my experience really don't like to pick up air in the suction.

    In the last picture in the first post is the injection pump. In the center of it, right above the oil pressure switch in the picture, is the inlet nut.

    Loosen that or even pull it off a little bit and pump the transfer pump until you get good solid fuel out of there.

    Then put it back on tight and it should start up pretty quick. I have never found the need to crack injector lines but you can try if it proves to be stubborn.

    Beware of disturbing the inlet and outlet lines to the square filter because they have a rubber compression ring and they might leak and have to be replaced and not real easy to find.
     
  8. skobydog

    skobydog Active Member

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    I see where you are saying to loosen inlet nut. I've read that many injection pumps have bleeder screws to purge at the pump. I haven't found any on this Stanadyne so loosening the line makes sense.

    When I was looking up Stanadyne pumps I came across this picture where it shows you can bleed at the return line (I circled the inlet with green and the return is the red circle). The return is a little higher so maybe bleeding there would be a better option?

    I'll probably crack the injector lines because this machine can be stubborn to start regardless.

    I'm probably overthinking this. I know I just need to get the air out but also don't want to loosen the wrong nut, bolt, or line. I read where someone loosened the wrong bolt on his injector pump and had to pull the whole unit off and bring it to a diesel repair shop. Thanks

    004.jpg
     
    Last edited: Apr 15, 2018
  9. Birken Vogt

    Birken Vogt Charter Member

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    TPGsc has not stepped in here but my understanding of this pump is that the first thing the fuel comes to after the center inlet nut is a vane pump, kind of a lame transfer pump part 2.

    This vane pump does not pump air very well and any air that is trapped ahead of it will take forever to purge so getting fuel right to that point will allow it to start pumping fuel and then the very next thing it does is to start going to the injection pistons so it may well pick up and take off if you do that. Conversely you can pump and pump the separate transfer pump and nothing can pass through the vane pump if the engine is not rotating.

    The housing bleed screw is that slotted screw in the black and white picture at about the 4 o'clock relative to the red circle but near as I can tell it doesn't do anything different than the return line to the tank so I seldom mess with it. But you can remove it and observe fuel flow if you are not sure if the injection pump is getting fuel, any time the engine rotates, solid fuel should dribble out that screw hole.
     
  10. skobydog

    skobydog Active Member

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    This pretty much confirms what you described in removing the inlet line for bleeding. The filter outlet is a bit higher but I don't want to disturb that connection if you think it may leak.

    When bleeding at the injectors it's saying to open the throttle wide open and crank the engine to purge the air. I guess the transfer pump is only for supplying fuel to the injector pump?

    005.jpg



    This was from a John Deere manual and also states this is for Stanadyne rotary pumps. The difference is they're saying to bleed at the return line. Not sure why it's different.

    005.jpg
     
    Last edited: Apr 15, 2018
  11. skobydog

    skobydog Active Member

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    So I guess this is why the instructions I posted say the engine needs to be cranked to bleed at the injectors..........
     
  12. Birken Vogt

    Birken Vogt Charter Member

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    Well, in theory, the pump only so much fuel into the injection line per stroke.

    If the line is full of air it will push it in but never reach nozzle opening pressure and spring back into the pump when the injection event completes, thus never purging the high pressure injection lines.

    In practice, once you get good fuel to the pumping elements, whatever they are, the engine will start, in my experience. I suppose they still have a considerable amount of fuel in them because once the pump runs out of fuel it cannotreally pump the fuel out and the high pressure lines full of air.

    So the long and short of it, don't overthink it, just get fuel to the central nut with the priming lever, tighten it up, and let it rip.
     
  13. thepumpguysc

    thepumpguysc Senior Member

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    As long as you have fuel TO THE INLET of the inj. pump, the inj. pump will take it from there..
    You just have to get the AIR out of the lines GOING TO the injectors..
    Loosen a couple or ALL of them & crank the engine till fuel squirts out & tighten..
    Have the throttle wide open.
    I would leave the return alone.. The pump will bleed itself..
    Good luck.
     
  14. skobydog

    skobydog Active Member

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    I have a much better idea of how the fuel system operates now. Thanks everyone, hopefully this is the last you'll hear from me. :)
     
  15. Birken Vogt

    Birken Vogt Charter Member

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    No, you have to come back and tell us how it went after you have it running again, you can't leave us hanging.
     
    Buickspec6231 and kshansen like this.
  16. skobydog

    skobydog Active Member

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    Ok, will do. Looks like Wed as long as the weather permits.
     
  17. kshansen

    kshansen Senior Member

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    Yes as Birken says be sure to let us know what you did and what worked. Nothing pi$$e$ of many people as giving advice and then never knowing if it worked. Also this is not just to give warm fuzzy feelings to those that have helped. Someone else five years from now might find this site while trying to solve the same problem and your reply might be just the information they need to fix their problem!
     
  18. thepumpguysc

    thepumpguysc Senior Member

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    last time, huh?? Until the flex ring goes out..
    I see the lead seals on you pump have ADS stamped/pressed in them.. which means the pump has been off before & taken into an ADS shop.. Hopefully they put in a solid weight retainer?? {EID}
    IF NOT.. We'll be see'n ya..
     
  19. kshansen

    kshansen Senior Member

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    Some people have good eyes! Not that the letters on the tag would have meant anything to me! But it is always good to know there are people out there who can spot things like that.
     
  20. skobydog

    skobydog Active Member

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    Pulled the inlet line off and manually started pumping the lift pump. It felt like I was only pumping air and no fuel was coming out.

    Checked the fuel tank and it's pretty much empty even though I put a good 5 gallons in last week. I'm not sure why there's no fuel, I didn't have a leak before.

    Right now there's snow on the ground and the machine is soaked. It will be a few days before things dry out. Hard to find a leak in this weather.