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Fuel Pressure Switch Issues

Discussion in 'Ocean Yacht' started by Matt Clark, Jun 17, 2023.

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  1. Matt Clark, Jun 17, 2023
    #1
    Matt Clark

    Matt Clark Member

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    I have a 1990 44 Ocean with 671 Detroit’s and have replaced the starboard engine fuel pressure switch three times in the last year and a half so apparently I need to keep some extras on board. Interesting that the original manufactured part on the port engine has never needed to be replaced and the newer replacement switches don't seem to last long. Anyone having the same issues? I understand the importance of the fuel pressure switch is so you don't restart the motor when it's already started so I'm be nervous to bypass that. Thoughts?
  2. Capt Ralph, Jun 17, 2023
    #2
    Capt Ralph

    Capt Ralph Senior Member

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    What brand was on originally?
    Nason, Honeywell (Hobbs), TecMark, Danfoss,,
    All have good / bad batches of lil switches.

    How do you know yours is bad? Hit the starter while running?
    Or N-C and closed to start, then you can't start.
    You may be over amping the switch.


    Also, on lots of V installs, some fuel pressure switches sticks out like a sore thumb, always getting knocked while it stabs you in the leg.
  3. Matt Clark, Jun 18, 2023
    #3
    Matt Clark

    Matt Clark Member

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    Ok thanks. I will check the brand of original and replacement. Mechanic is telling me it was bad as I had nothing when I hit the start switch and since this has happened a few times before when I put in a new switch and it immediately solved the problem. One time I did by pass the switch to get home as I was on a trip.
  4. Capt Ralph, Jun 18, 2023
    #4
    Capt Ralph

    Capt Ralph Senior Member

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    Just came to mind;
    Do you have dual starter solenoids?
    Would you have a schematic of what you have?
    On lots of heavy duty installs, a small solenoid is connected to the start switch, This small (low current draw) solenoid drives the big starter solenoid.
    If your pressure switch is over amping then failing, then this may help.

    My Detroit's have 3 solenoids. Further insurance keeping the starter motor from running away.
    Amazing what the mfgs were thinking 45 years ago.
  5. RichV, Today at 8:51 AM
    #5
    RichV

    RichV Member

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    Capt Ralph, can you elaborate on the 3 solenoids for the starter? I'm looking for a work-around for the blown pressure switches.

    Whenever there is extra cranking involved in starting, the high amperage on the 2 AWG wire from the starter through the fuel pressure switch, fries it. After replacing several, it's been bypassed for a couple years now. I want a more permanent solution, I've already hit the start accidentally while running. One mechanic told me it was designed as a protection for the old alternators.

    The simplest seems to re-wire the pressure switch through the circuit from the start switch to the solenoid?
    Last edited: Today at 8:58 AM
  6. Capt Ralph, Today at 9:01 AM
    #6
    Capt Ralph

    Capt Ralph Senior Member

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    Melting #2 wire?
    What does this wire connect exactly from point to point?
  7. RichV, Today at 9:07 AM
    #7
    RichV

    RichV Member

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    No, it doesn't melt the wire, it just fries the pressure switch. The heavy gauge wire tells me it's carrying a lot of current.

    Attached Files:

  8. Capt Ralph, Today at 10:58 AM
    #8
    Capt Ralph

    Capt Ralph Senior Member

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    That looks like the same Nason Switches I use all over my 12V71s.
    Your heavy gauge wire is probably more to reduce voltage drop than high current.

    And your stating fuel pressure switch and not oil pressure switch?
    Do you have a print set or schematic for your install?

    Can you describe the installation; From start switch, to pressure switch, to first solenoid, to starter solenoid?
    Or, As I fear; From start switch, to pressure switch, to starter solenoid?

    Where is your boat? Were heading south in a few days.
    In in FL east coast maybe I can offer an extra hammer. Detroits respect hammers. ☺☺
  9. RichV, Today at 11:10 AM
    #9
    RichV

    RichV Member

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    My boat is in Massachusetts. I will take some pictures today and draw a diagram.

    BTW, I have 6-71TIs.
  10. Capt Ralph, Today at 11:13 AM
    #10
    Capt Ralph

    Capt Ralph Senior Member

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    I was raised on 6-71s.
    You can near do anything with them and they ask for more.

    Oh, what voltage is your boat / engines??
  11. RichV, Today at 6:03 PM
    #11
    RichV

    RichV Member

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    The wires are actually 6 AWG. One wire comes the start switch solenoid to the fuel pressure switch, and the second returns from the switch to the starter solenoid. I measured 15 amps when cranking. Normally the fuel pressure switch handles that ok, but any time there is extended cranking, the FP switch craps out.
    12 volt system 6-71TIs
    Orange wires to solenoids.

    What if I just put the FP switch in line from the start button to the first start solenoid?

    Starter Solenoids.jpg FP Switch Bypass.jpg
    Last edited: Today at 6:08 PM
  12. Capt Ralph, Today at 6:56 PM
    #12
    Capt Ralph

    Capt Ralph Senior Member

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    Back at my desk. I see your pics. Give me a few and I'll be back.
  13. Capt Ralph, Today at 7:38 PM
    #13
    Capt Ralph

    Capt Ralph Senior Member

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    Ocean Yachts had many innovations on house/starter voltages.
    I'm trusting you have the simple all 12V system.
    The idea of the first solenoid is to ensure low current drain on the yellow/blk stripe wire thru the helm.
    The out of this first solenoid delivers max voltage to the main starter solenoid.
    It usually does not take much current to close this first/helper solenoid. When it closes, max current is delivered to the starter solenoid for no issue starting.
    Your Nason pressure sender ensures that when pressure (oil or fuel) is pushing it open, the first helper solenoid can not engage the starter.
    Below is my first impression on what you may have by-passing the Nason switch;
    PhotoScan.jpg
    Last edited: Today at 7:48 PM
  14. Capt Ralph, Today at 7:44 PM
    #14
    Capt Ralph

    Capt Ralph Senior Member

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    With the working Nason switch, All works till the switch is opened (fuel or oil pressure) then the first solenoid does not work untill the pressures are reduced.
    Still this is a low current path from the helm to the first solenoid controlled by the pressure switch.

    with switch.jpg
    Last edited: Today at 7:52 PM
  15. RichV, Today at 7:47 PM
    #15
    RichV

    RichV Member

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    Maybe the older pressure switches were more durable? Like I said, it all works fine except when there's a starting problem, and there is excessive cranking. I'm not the only one who has this problem.

    Where is the pressure switch (normally closed) in your diagram?

    It's drawing 15 amps. Is that more than it should?

    Thanks
  16. RichV, Today at 7:50 PM
    #16
    RichV

    RichV Member

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    You put the pressure switch before the first solenoid. That's the change I'm proposing.
  17. Capt Ralph, Today at 8:03 PM
    #17
    Capt Ralph

    Capt Ralph Senior Member

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    In your picture, you show two leads of heavy cable tied together? Hopefully the Nason switch did not fit here?
  18. Capt Ralph, Today at 8:06 PM
    #18
    Capt Ralph

    Capt Ralph Senior Member

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    That is where it should be, not in a heavy current path.

    Pending what was on Ocean Yachts minds that week, The pressure switch should be switching either B+ or B- to that first solenoid.
    They also used this same switch to engage the hour meter. This may help you work backwards to prove miss-wiring. Is the other side working correctly? Can you back trace those wires?
    I'm sure they are not the same as your troubled side.
    Last edited: Today at 8:12 PM
  19. RichV, Today at 8:11 PM
    #19
    RichV

    RichV Member

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    The 6 AWG wires tied together are the ones that went to the pressure switch. I will try re-routing the pressure switch to before the 1st solenoid (after the start switch). I'll let you know how it works.
  20. Capt Ralph, Today at 8:14 PM
    #20
    Capt Ralph

    Capt Ralph Senior Member

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    I can be in Mass around 8 weeks out.

    Let me know if you need some heavy hammers.
    ☺
    rc
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