Alarm above 1,000 RPM
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Alarm above 1,000 RPM

  1. #1
    Member PDQH2O's Avatar
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    Default Alarm above 1,000 RPM

    Beautiful day in So Cal today and decided to take the boat out. It has been running perfect every time until now. idled perfectly out the main channel and began to throttle up. Over 1,000 RPM, I get an alarm and the ECM brings on the funk. Ran horribly, dropped back to idle; alarm shuts off and runs perfectly again. Tried a half dozen times to get on plane. same results each time. Shut all power down at the Perko switch and powered up again; problem returned every time.

    Boat Conditions:
    2006 Mercruiser 496 w/Bravo 1 - 70 hours on it
    Fuel = full
    Alternator = 14 V
    Temp = approx 165 degrees
    Oil pressure = 40 psi, full level
    Trim = 80% down,
    Outdrive fluid level = full


    Trailered it back home, washed the boat and flushed the outdrive and trailer. With the muffs on and, started it up to recreate the problem. Lots of water flow through the exhaust. Idled perfectly. Went to 1,500 RPM ran perfectly. Slowly increased RPM to 3,000 still ran perfectly. Repeated this test at least three times and could not recreate the problem.

    Any ideas what might cause this? Saw in another thread that the shifter sensor might cause a similar problem, but in the 3,000 RPM range. Could this be the cause? Time for a trip to the shop?
    Last edited by PDQH2O; 01-17-2009 at 09:23 PM.

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  3. #2
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    Our 2002 450 hour 350 mag motor did the same thing this past summer. Very very similar.

    Took it back to my dealer. Forget exactly what it was. Switch or some sort in the fuel injection. He struggled to find it-- intermittent until he did a wire wiggle.. Sorry I didn't pay better attention. Might be able to call him and review the bill, if you don't have any luck.

    Good luck
    Is it just me or are toilet seats getting smaller?

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    Senior Member GT Jets's Avatar
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    Loose power connection somewhere in the battery circuit, sounds like an auxilliary power lead to the ECM, I would check the tightness of the battery cables at the starter motor first...Possibly a loose ground.

    Could also be a linkage misalignment for foward, neutral and reverse...check for proper adjustment in forward..

    You did not mention if it revved up in nuetral in the water, did it only have the problem in gear?

    GT
    GT


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    Senior Member TwinTurbo540's Avatar
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    Check the drive oil!!! Almost 100% thats what it is, low drive oil sending a signal to the computer. Been there before!

    Travis

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    Member PDQH2O's Avatar
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    Quote Originally Posted by GT Jets View Post
    Loose power connection somewhere in the battery circuit, sounds like an auxilliary power lead to the ECM, I would check the tightness of the battery cables at the starter motor first...Possibly a loose ground.

    Could also be a linkage misalignment for foward, neutral and reverse...check for proper adjustment in forward..

    You did not mention if it revved up in nuetral in the water, did it only have the problem in gear?

    GT
    GT Jets - I'll try the battery connections today. Probably won't know if that's the problem for sure until I get it back in the water.

    I didn't try revving it in neutral while in the water. On the trailer it seemed to have no problem revving.


    TwinTurbo540 - The Drive oil was just below the line on the resevoir, but I wouldn't think enough to set off an alarm. Could be wrong though.

  8. #6
    cfm
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    Definately have to get the computer scanned for trouble codes. Then go from there.

    These 496's have an intricate ECU system that checks many things other than just your typical. Example: It even checks the water going into exhaust for proper water flow.

    Yes, as mentioned above, low drive gear fluid can/will set alarm, amongst many other things.

  9. #7
    cfm
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    Quote Originally Posted by PDQH2O View Post
    On the trailer it seemed to have no problem revving.
    This doesn't tell you anything other than it revs with no load vs under load. It takes ultra little power to rev engine in neutral. Things can be way out of whack and engine still seem fine under no load conditions.

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    Member PDQH2O's Avatar
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    Quote Originally Posted by GT Jets View Post
    You did not mention if it revved up in nuetral in the water, did it only have the problem in gear?
    GT
    After checking everything I could think of, including tips offered in this thread, put the boat in the water to test under load. Alarm still sounds and Guardian mode (computer reduced power) engaged. Same result in forward, neutral and reverse. Tried slow and normal acceleration, no difference.

    Looks like it's time for a dealer visit.
    Last edited by PDQH2O; 01-20-2009 at 01:59 PM.

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    Senior Member TwinTurbo540's Avatar
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    Did you get some bad gas? Is it a knock sensor talking to the computer? I have seen that happen before as well!

    Travis

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    It's what we do BDMarine's Avatar
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    The 496 has a PCM module. It can be checked by most scan tools but really only fully diagnosed by a dealer with a laptop and the Merc CDS system. It can go back in the history and freeze frame the problem if it was stored.
    Should be done by a Certified, Premier Dealership like......
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    B & D Marine Performance
    El Monte, Ca.

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    If you actually 'rev-d it to 3K' it should have sounded an alarm. When out of gear the motor cannot be free rev-d above 2500RPMs, or a BEEP will be heard. It will also put a 'code' in history and/or freeze frame if done for a second or two. I'm thinking you have "failed seawater pump pressure strategy" and that will cause the alarm and a % of Guardian. Get the thing IN THE WATER and ON A DDT or CDS, either one will tell you what and why the boat is doing these things. Also, EVERY TIME you have it serviced, the "codes" and "history" should be 'printed out' and then CLEARED. So you have a record of what your motor is doing and how it is doing.

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    Had a Cigarette boat, with the water temp sender wiring short to ground, this sounded an alarm.

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    Just thought of another thing .... If you have an 'in line fuel filter' that has not been replaced it may be starving for fuel. If the in line filter is restricting fuel flow durring 'engine loading', the "PCM" will not SEE FUEL PRESSURE, but it will FEEL LEAN KNOCK. Heavy 'lean knock will trigger the PCM to react with Guardian. Get it to a shop ON THE WATER (actual conditions) now!

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    Quote Originally Posted by TwinTurbo540 View Post
    Did you get some bad gas? Is it a knock sensor talking to the computer? I have seen that happen before as well!

    Travis
    Gas is fresh, from a major brand name. Sta Bil was added at 1/2 tank for storage. Tank was then filled the rest of the way.

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