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  1. #1
    Bobtail Member
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    Cummins Fuel Issue

    Hey everyone. This is a two part question.
    1. We have a 2000 Volvo 770 with a 600 ISX Cummins (Signature Series). There is a fault code that says there is a low fuel delivery. About half of the time the truck runs great and couldn't run smoother. The other half, it runs rough like there is a big cam in it. It will do this at an idle and also going down the road. For this year motor (1999), Cummins had to add an electric fuel pump because they had trouble with the motor running. So now this has an electric fuel pump that pumps the fuel to a mechanical pump. The mechanical pump has been changed so does this mean that the electrical pump is going bad?

    2. Is there a difference between a priming pump and a lift pump or are these both the same thing?



    Thanks!

  2. #2
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    Both the priming pump and the lift pump are the same thing. It only runs for a set amount of time when you key on. Once the engine starts it stops running.

    Is it running bad on a few cylinders when it does run bad or does it run bad on all cylinders? If it is just a few it might be one of the solinoids that controls the fuel to the injectors.

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  4. #3
    Have a Cup Of Concrete
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    Quote Originally Posted by Cummins600 View Post
    Hey everyone. This is a two part question.
    1. We have a 2000 Volvo 770 with a 600 ISX Cummins (Signature Series). There is a fault code that says there is a low fuel delivery. About half of the time the truck runs great and couldn't run smoother. The other half, it runs rough like there is a big cam in it. It will do this at an idle and also going down the road. For this year motor (1999), Cummins had to add an electric fuel pump because they had trouble with the motor running. So now this has an electric fuel pump that pumps the fuel to a mechanical pump. The mechanical pump has been changed so does this mean that the electrical pump is going bad?

    2. Is there a difference between a priming pump and a lift pump or are these both the same thing?

    Thanks!
    My electric pump hasn't worked for over a year..
    They are only a primer pump to stop the typical long crank before firing that cummins do.

    sounds like you are sucking air in or are running with a high restriction in the fuel system.

    There are a few different fuel filters available for these things, you must be sure to get the high flow version ( don't remember the numbers and my truck isn't here to look ).

    at idle, i can cause the lumpy cam thing to happen by putting the slightest pressure on the pedal, so you might have a bad connection somewhere in there also.

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  6. #4
    Road Train Member dave26027's Avatar
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    Look for an air leak in the fuel line between the tank and primer pump, and blow out the fuel tank vent tubes (carefully) with compressed air. There are 2 kinds of fuel lines, I'm not sure which type you've got- standard lines have brass ends. Check the connections for dents or cracks that suck air. The other type has plastic lines with copper collars in the connections. They often get crushed the wrong way when they are tightened and will leak. What's happening is that the fuel level in your filters gets lower and lower due to the leak sucking in air. Eventually, air ends up going to the injectors. Because fuel has a lot of detergent in it, it foams and gets injected as foam instead of fuel. Eventually it'll cavitate your injectors.
    If you want the best fix for the problem, install a FASS system from Pittsburgh Power. Don't forget to look at Fuel Preporators, too. Both of them strain the air and foam out of the fuel before the transfer pump picks it up. If you notice the fuel level in one tank higher than the other tank, it's a sure sign of a problem.
    Good luck !

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  8. #5
    Bobtail Member
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    Thanks everyone for the quick responses! When the truck runs bad, it seems to run bad on all cylinders. I don't know if this helps but when we the truck has a lot of fuel in it, it runs better.

  9. #6
    Medium Load Member Starline's Avatar
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    Once upon a time I had fuel issues as well (N14) and this is what I did to resolve it besides replacing the fuel filter... speaking of, I believe it was Lube Refiner has a bad batch of fuel filters, I switched to Baldwin or Donaldson.

    1, replaced fuel lines and made sure there was no restrictions in the pickup tube.

    2, Fuel check valve, trash can get caught in it since your fuel goes from the tank into the back of the engine first before exiting the side of the block to the fuel filter then the pump... On a N14 anyhow. All you have to do is follow your lines to see .

    3, Installed a DAVCO 842 between the tank and the engine to catch excess water and trash BEFORE it reached the engine ($100 at junk yard). You wouldn't believe what has come out the bottom of this filter over the years.... water, algae, kitty litter or quick dry, unidentifiable trash


    All it takes is 1 bad tank of fuel... Cummins like clean free flowing fuel.

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  11. #7
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    I have a Volvo 770 with a 500 Cummins ISX and I have the same problem like you.
    I went to Cummins 3 times , they first changed the secondary fuel pump and connections with no result , the second time they again changed the secondary fuel pump again with no result and the third time they changed my Davco 382 fuel separator and I have the same problem. In the transparent fuel line that they installed you can clearly see air in to diesel. Once the secondary Fuel pump is bypassed there is no air in fuel anymore,same goes with the davco separator, strange stuff.

  12. #8
    Bobtail Member
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    You might want to see if your fuel pick up line is cracked

  13. #9
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    Quote Originally Posted by Narcis.M View Post
    I have a Volvo 770 with a 500 Cummins ISX and I have the same problem like you.
    I went to Cummins 3 times , they first changed the secondary fuel pump and connections with no result , the second time they again changed the secondary fuel pump again with no result and the third time they changed my Davco 382 fuel separator and I have the same problem. In the transparent fuel line that they installed you can clearly see air in to diesel. Once the secondary Fuel pump is bypassed there is no air in fuel anymore,same goes with the davco separator, strange stuff.
    I just changed yesterday all the fuel lines and fitings from the tanks to the fuel pump,everything is brand new now and I still have the same problem.It does this also with the tanks full with diesel so I don't think that is the fuel pickup line from inside the tanks.If somebody have an ideea please Lmk.TY

  14. #10
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    Found the problem ,it was the fuel shut-off solenoid , the one that cut the diesel when the ignition key is turned off .

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