Help! 496ho won't go over 4000 rpms or over 40mph
+ Reply to Thread
Results 1 to 12 of 12

Thread:
Help! 496ho won't go over 4000 rpms or over 40mph

  1. #1
    Member
    Join Date
    Jun 2008
    Posts
    34

    Question Help! 496ho won't go over 4000 rpms or over 40mph

    Max rpms 4000. No beeping or anything. Hooked to computer and no codes. Changed spark plugs and new fuel. Same thing. Help?!

  2. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  3. #2
    New here Beer:30's Avatar
    Join Date
    Feb 2008
    Location
    Bakersfield, CA
    Posts
    4,219

    Default

    Quote Originally Posted by dannyo View Post
    Max rpms 4000. No beeping or anything. Hooked to computer and no codes. Changed spark plugs and new fuel. Same thing. Help?!
    What's the fuel pressure - KOEO?
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

  4. #3
    Senior Member TNYoungblood's Avatar
    Join Date
    Mar 2010
    Location
    Clarksville, TN
    Posts
    5,110

    Default

    Check your linkage/throttle cable and check your timing
    WFLC The REAL #321 Kentucky Drag Boat Association 2016 NJBA 10.0 High Points Champ

  5. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  6. #4
    Member
    Join Date
    Jun 2008
    Posts
    34

    Default

    Sorry. How do I check that? I don't think I have a gauge?
    Thanks, Dan

  7. #5
    Member
    Join Date
    Jun 2008
    Posts
    34

    Default

    Throttle cable was replaced recently and ran great last 2 trips.

  8. #6
    New here Beer:30's Avatar
    Join Date
    Feb 2008
    Location
    Bakersfield, CA
    Posts
    4,219

    Default

    Quote Originally Posted by dannyo View Post
    Throttle cable was replaced recently and ran great last 2 trips.
    If you don't know how to check the fuel pressure, don't bother. Have someone check it next time during service.

    The next thing I was going to mention is - throttle cable....has it been touched recently?? Without guardian codes (beeping and limiting RPM), it can really only be lack of full throttle extension from the cable. My bet is it came loose.

    Disregard the timing, you can't check that without being hooked up to a laptop. No distributor whatsoever.
    Last edited by Beer:30; 05-19-2012 at 07:33 PM.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

  9. #7
    gn7
    gn7 is offline
    Senior Member gn7's Avatar
    Join Date
    Jan 2008
    Posts
    25,975

  10. #8
    Member
    Join Date
    Jun 2008
    Posts
    34

    Default

    Thanks for the suggestions. Plugs changed, Fuel pressure stable, no misfires when lake tested. Gonna Compression test but still can't figure it out.

  11. #9
    Senior Member
    Join Date
    Jan 2008
    Location
    Quartz Hill/Havasu - Where Life Leads US
    Posts
    151

    Default

    May want to check the water pressure sensor. On the HO there is a little T that checks that verifies water pressure on the intake. Mine has developed calcium and the boat felt like it wanted to come off plane and not go any faster. Once cleaned all was good.

  12. #10
    Member emilsr's Avatar
    Join Date
    Jan 2012
    Location
    El Paso
    Posts
    59

    Default

    4k rpm/90% power is soft guardian mode. Surprised that it didn't throw a code assuming your throttle is open all the way.

  13. #11
    Member
    Join Date
    Jun 2008
    Posts
    34

    Default

    Will check water pressure. Yes, no codes at all.

  14. #12
    Member emilsr's Avatar
    Join Date
    Jan 2012
    Location
    El Paso
    Posts
    59

    Default

    That's odd....

    I know the software varied a bit through the years ('01-'11) and have heard a couple of stores about the IAC going bad without any beeps or logging a code in certain years. This put the 'puter in soft guardian mode. A friend had this happen recently in a 2003 model boat....chased the problem for over a month.

    Hate to even suggest just throwing parts at it, but if nothing else take the IAC to your local NAPA or VatoZone and cross reference the part number. Mercruiser sells them for about $100, but it's a Ford part and NAPA has them for about $60 (last time I checked). Once you install it you'll need to have the 'puter reset to take it out of guardian.

    .....if that's even it. Hopefully you'll find something simple before then.

+ Reply to Thread

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Please select your insurance company (Optional)

Log-in

Tags for this Thread

Digg This Thread

Posting Permissions

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
  •  
 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95