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  1. #1
    Registered Peconic's Avatar
    My Boats:
    2003 290 Kryptonite
    Join Date
    Oct 2002
    Quogue, NY

    Mercury Engine Computer Quirks

    I am working on an article about the PCM555 engine computer w/ Mercury engines. This article centers on the computer on the Mercury Racing HP525 under racing conditions. The article might also be interesting for owners of 496 etc. engines.

    I am seeking feedback from other owners re:

    - Have you experienced spurious (intermittent) sensor problems that could not be traced back to a bad sensor or wiring? (I.e.: The computer reports a sensor problem that is none.)

    - Has your engine entered Guardian mode because of a sensor problem that could not be traced back to a bad sensor or wiring?

    - Could this be rectified, and if so, how?

    - Do you know of any steps to avoid spurious sensor problems?

    Thank you!

  2. #2
    Registered Tricky919's Avatar
    My Boats:
    I Have No Boat
    Join Date
    May 2003
    Port Chester, NY.
    i'm not sure if this is any help or has anything to do with your situation but i have 496's in my boat and was experiencing intermitent engine problems after 4000 rpm's. After having the computer checked with the diagnostic tool it came up negative except for one time the gardian was engauged. I found out that there was debree clogged on the screen at the fuel pump in front of the water seperator, if you follow the line from the tank to the pump and remove the barbed fitting you will see the screen which is designed to save the pump. They now have a in line stainless filter before the pump that should be installed. I cleaned the screens and the moter runs great again. If anyone ever expirences rpm problems or fuel delivery problems with the new 496's start with checking these screens, it will save you a lot of time and headaches...........Ricky..........

  3. #3
    Registered Peconic's Avatar
    My Boats:
    2003 290 Kryptonite
    Join Date
    Oct 2002
    Quogue, NY

    Guardian won't let you get much above 4200. When in Guardian, I can bring it to 4500 briefly, then it backs off to 4200. That's on the HP525.

    I don't have the list of what causes Guardian on the 496. On the HP525, a fuel pump or fuel injector failure would sound the horn 5 times, a fuel pressure sensor failure would result in 3 beeps. Guardian would not be engaged.

    Next time they do a scan and they find a fault, ask for the "freeze frame" data. When a fault is recorded, the PCM555 records the pertinent data of the other sensors along with the hour meter etc.

    Intermittent engine problems due to a clogged fuel line is a "real one."

    What I am researching are problems that are no problems. The engine computer turns them into problems by switching into Guardian without a reason.

    While pleasure boating, this might no be a problem. You restart, the problem goes away. While racing, it is a huge problem. You restart, the problem goes away, your winnings go away.
    Last edited by Peconic; 08-24-2003 at 09:25 AM.

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