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Air Pressure Aft Filter in WC -Man

Discussion in 'Engines' started by Marblehead01945, Oct 4, 2020.

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  1. Capt J

    Capt J Senior Member

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    To check, run it without the air filter. Also if your mechanic is very heavy handed with the K+N oil, it can clog the sensor. If it's not the air filter, change the sensor. I usually see 5 or less.......
  2. mapism

    mapism Senior Member

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    Beware, what your mechanic is saying clashes with the explanation given by v10builder1.
    Now, I can't be positive about which of these alternatives is correct, but certainly the latter makes good sense.

    And I wouldn't rely on the fact that one display shows '-1' to deduct that the value is supposed to be negative, either.
    One inch WC is less than 0.04 psi, i.e. close to nothing. So, the defective sensor could well be the stbd one, which isn't reading anything.
    Pulling the filters as CJ suggested should give you a good baseline, anyway.
  3. Capt J

    Capt J Senior Member

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    I've also seen filters that looked perfect, but were totally clogged. You can only clean them so many times and they eventually will implode into themselves at cruise.
  4. Marblehead01945

    Marblehead01945 Member

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    I have been slow to get to the boat but here is another data point- Engines off Port engine 22, Starboard at zero. I would expect with engines off both would be zero. Engines on 800 or so RPM's- Port 22, Starboard -1. This is before swapping airfilters which I don't think I am going to bother with at this point since the engine off Port engine cannot possibly be true. Still looking like the sensor to me.
  5. Pascal

    Pascal Senior Member

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    Definitely sensor or connector.
  6. v10builder1

    v10builder1 Senior Member

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    Inches of WC is an English unit - not metric. The browser (Chrome) I user only shows a piece of the post #1 photo - what I see I believe to be the starboard engine showing running RPM with 19 in. WC and a green bar under the 19 - apparently indicating the value is OK, but as posted by Fiammetta42, best practice is to record the value with new air filters (19 in. WC is 47.1 millibars).

    Common sense will tell you that there will be suction, not be positive pressure, immediately downstream of the air filter with the engine running.

    The values seen on the displays with the engines off may or may not be relevant depending on the program/programmer, but the value seen at the sensor with the engine off would be 0 in. WC, -1 is close enough.

    To restate what has been said before, the voltages and currents used in these sensor circuits are often very small, so connections are critical. The sensor environment is not too extreme, but salty air is what it is. Hope for a wire/connection issue - might be practical to test sensor by swap.
  7. Marblehead01945

    Marblehead01945 Member

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    I forgot to update this but we replaced the sensor yesterday and all is well.
  8. Capt Ralph

    Capt Ralph Senior Member

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    There ya go. Our new MAN tech.