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  1. #1

    Default 8.1 MPI oil pressure switch/sender

    My port side engine runs at 40-43 PSI at 3,200 RPM. My starboard runs at almost 50 PSI at 3,200 RPM. I wouldn't expect it to be exactly the same but I would like to see it a little closer. So I want to rule out the oil pressure sender and gauge. Looking at the parts diagram there are two different kinds of pressure senders. An "SS" and a "DS" and there is also a pressure switch that looks like it only goes with the "SS". I don't want to have to run down to the boat and take a look at it. Is there anyway of know what type I have without a physical inspection?

  2. #2
    Join Date
    Sep 2008
    Location
    Maryland - USA
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    Default Re: 8.1 MPI oil pressure switch/sender

    SS & DS are Single Station and Dual Station Sender units for the gauges.

    Switches are either ON or OFF and typically don't care how many helm stations exist....

  3. #3

    Default Re: 8.1 MPI oil pressure switch/sender

    Thanks Mark. As usual you are a big help.

  4. #4
    Join Date
    Sep 2008
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    Default Re: 8.1 MPI oil pressure switch/sender

    Glad to help.....FWIW, the switches are typically used to indicate a setpoint exceedance.....either to the warning horn for overheat, low oil pressure, or the ECM....my guess is as designator like SS tied to a switch was an editorial oversight....

    A quick check on your sender/gauge concern is to swap the sender wires at the gauges.....another item that can impact accuracy is the wiring of the gauges.....bad ground or B+ wires will induce errors.....

  5. #5

    Default Re: 8.1 MPI oil pressure switch/sender

    Quote Originally Posted by makomark View Post
    Glad to help.....FWIW, the switches are typically used to indicate a setpoint exceedance.....either to the warning horn for overheat, low oil pressure, or the ECM....my guess is as designator like SS tied to a switch was an editorial oversight....

    A quick check on your sender/gauge concern is to swap the sender wires at the gauges.....another item that can impact accuracy is the wiring of the gauges.....bad ground or B+ wires will induce errors.....

    Thanks Mark. That was going to be my next course of action.

  6. #6
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    7,754

    Default Re: 8.1 MPI oil pressure switch/sender

    As far a checking the gauges, most use the American standard.....with power ON, a 33 ohm resistor between S (w/ no other wires connected) and GND should give you full scale and a 240 ohm resistor should give you the min scale reading.....sender usually have a 10% tolerance on them regarding accuracy...

  7. #7
    Join Date
    Jun 2008
    Location
    Island Heights, NJ,
    Posts
    3,066

    Default Re: 8.1 MPI oil pressure switch/sender

    ... and given the gauge technology, not likely the gauge any better accuracy, therefore, sender plus gauge accuracy can be anywhere up to 20% off, or @ 40 psi, +/- 8 psi. Then you have to add in the tolerance for the voltage on the electrical system... and any variable losses in the wiring and connections.
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280

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