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Man Engine Gauge "air pressure after filter" question

Discussion in 'Technical Discussion' started by CSkipR, Jul 4, 2019.

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  1. CSkipR

    CSkipR Member

    Aug 16, 2008
    New Smyrna Beach, Fl
    What does the "air pressure after filter" identify on my Man eng gauges. What should the normal reading be and what improves it or makes it worse? When at cruise mine is "0 " although some Mans have a higher number on their motors and some with a negative number.
  2. Capt Ralph

    Capt Ralph Senior Member

    Sep 8, 2004
    Satsuma, FL
    Combination purposes I think.
    Air filter restriction.
    Altitude air pressure.
    Alarm system between air in and boost pressure after turbo.
    Maybe more.

    I would think a large negative value is bad, like dirty air filters.
    I like Zero.
    I would think a positive number is either read in error (didn't see the minus sign) or the system needs zero calibration.

    However, the computer is in charge of all of these values. if it runs, nothing is broke.
    Go Fishing, it's pretty down there today and I've seen the fireworks in your hood. Have fun.

  3. Capt J

    Capt J Senior Member

    Jul 11, 2005
    Fort Lauderdale
    It's the sensor right after the air filter. It indicates a dirty air filter and when it's time to clean it, OR if there is another air flow restriction before the air filter, such as the engine room vents not being adequate...…..they usually run -2 to -4 on all of the MAN boats I've ever run. Occasionally these sensors do go bad (like every 10 years), OR someone got overzealous with the air filter oil and it ruined the sensor. Zero is perfect as you have zero restriction.
  4. BoulderGT3

    BoulderGT3 Senior Member

    Jun 19, 2014
    It measures vacuum downstream of the air filter. A greater negative # equals a dirty air filter. IIRC it alarms at -1.5bar. Here's a pic of mine with freshly cleaned airseps.

    Attached Files:

    Last edited by a moderator: Jul 5, 2019