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Losing prime...?

Discussion in '7.3L Powerstroke Diesels' started by m67tang, Jan 15, 2020.

  1. m67tang

    m67tang Full Access Member

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    I’m losing prime on my 7.3 obs. Does that mean time to rebuild the repair the fuel bowl?
    I know it’s a basic question, but PSD stuff is totally new to me. Online seems like it’s 99% likely the drain valve. I smell fuel, but don’t see a leak under the hood.
     
  2. greenskeeper

    greenskeeper Full Access Member

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    Look carefully in the valley of the engine, especially underneath the fuel pump. They have a weep hole when they begin to fail that drips fuel. Best bet is to clean everything really well and fire it up....look for leaks and don't touch the fan blade!
     
  3. 79jasper

    79jasper Chickenhawk

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    Is the fuel bowl actually draining? Or is it just hard to start?

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  4. m67tang

    m67tang Full Access Member

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    I’m having no fuel prime/ starting troubles. Started all of a sudden.
     
  5. 79jasper

    79jasper Chickenhawk

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    What I'm asking is have you actually pulled the filter cap to verify fuel level in the bowl?

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  6. Oledirtypearl86

    Oledirtypearl86 Full Access Member

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    If the filter water seperator was leaking you'd see fuel in the valley also on the ground and Iv seen a few where the filter housing wasn't sealing at the lid usally due to not changing the o ring
     
  7. m67tang

    m67tang Full Access Member

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    Haven’t found anything obvious yet. Still looking.
     
  8. greenskeeper

    greenskeeper Full Access Member

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    As mentioned, how are you concluding that it’s “losing prime”? Are you sure it’s not “hard starting” and possibly a glow plug or relay issue?
     
  9. m67tang

    m67tang Full Access Member

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    Next time it happens, I’ll pull the fuel bowl lid and check fuel level. I’ve replaced the gp’s and harness. But I’ll check it out.
     
  10. greenskeeper

    greenskeeper Full Access Member

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    sounds good. I've seen these engines run when pouring out fuel or having zero fuel pressure....it'll still "run" but have now power due to lack of fuel flow.

    I'd be surprised if you are truly losing prime with no obvious leak.
     
  11. 13fcolt

    13fcolt former professional

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    I'd bet it's the CPS.
    When it goes out, the injectors don't fire, giving the appearance of no fuel.
     
  12. 79jasper

    79jasper Chickenhawk

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    His truck starts and runs, just takes cranking.

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  13. m67tang

    m67tang Full Access Member

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    Tell me about the CPS. I don’t know much at all about this PSD. Coming from IDI world. What’s it stand for???

    here’s what happened:
    Truck wouldn’t start. Like no fuel. I shot some spray silicone into the intake. Thinking I’d lost prime. It then fired right up. I’ve already replaced my GPs and harness. Seems to be ok starting last few days. But I smell fuel at the front grill after I shut it off. Don’t see any leaks anywhere. That’s all I got for now.
    Is this like a CPS?
     
  14. 13fcolt

    13fcolt former professional

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    CPS is Cam Position Sensor. I'ts located in the front cover just above and to the passenger side of the harmonic balancer.
    One 10mm bolt holds it. Do not over torque.

    The CPS is a hall effect sensor that reads dips cut into the face of the cam gear. This sends rpm and firing order to the PCM.
    When this little pain starts to go out, it is very much like what you are going through until it dies completely and wont start.

    1. Only use motorcraft or international from a reputable source as there are a lot of fakes out there.
    2. Always keep a good spare in the glove box.

    If nothing else, this one part makes me miss my idi.
     
  15. 13fcolt

    13fcolt former professional

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