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Thread: 496 HO Help

  1. #1
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    496 HO Help

    Guys

    I have a 2005 342 Boss with 496 HOs in it. The motors have roughly 250 hours. I recently changed out the IAC valves as my port engine didn't want to idle. That fixed the problem. I ran the boat a couple more times this summer with no issues. I went to run the boat this last weekend and I'm having trouble with the port engine. The engine starts and idles fine but when I increase the throttle with the boat in gear, the engine revs then immediately starts cutting out and RPMs fall off to idle. The boat starts giving a solid alarm. Once back at idle, the alarm finally goes off. All fluids are fine and the boat was just totally serviced out 15 hours ago. I'm assuming its a fuel or some sort of electrical / sensor issue. If anyone has any suggestions, it would be greatly appreciated.

    Thanks

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    PBN Charter Member BajaDan's Avatar
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    That is most likely (one man's opinion here) going to be a low water pressure situation triggering the guardian mode. I have also seen it on an over temp situation (pinched hose). In any event, it is something that makes the engine believe it is in imminent danger. It should leave an alarm code that can be scanned for and identified.

    But my bet is that either your sea pump needs to be rebuilt/replaced or you have a water restriction somewhere. Make sure the intakes are clear on the outdrive and try running it on a hose and see what sort of water flow you get.

    Good luck.

    Edit: That is particularly true if you have never had the sea pumps (or raw water pump as some call it) rebuilt. Merc says they are good for 300 hours but my experience indicates otherwise. Make sure to back flush the system to get the parts out of the oil cooler intake if you find rubber parts missing from the impeller before you put the pump back on the engine.
    Last edited by BajaDan; 11-08-2017 at 11:58 AM.

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    You must buy a scanner unless you want to hand the boat over to a mechanic.
    Rinda Technologies Inc. Marine and Industrial Engine Diagnostic Tools
    It's the best $500 you will spend on your boat; I guarantee it.

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    Thanks Dan. The pumps were serviced along with everything else about 15 hours ago. The Rinda scanner, is this something most all you guys have in order to work on these engines? Is this the best route or should I just go to my mercury mechanic?

    Thanks Sydwayz!

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    PBN Charter Member BajaDan's Avatar
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    Depends on if you want to work on it yourself and what the mechanic charges you for a scan. I have one but rarely use it and I do all my own work. So go figure?!

    Let us know what you find, I'm always eager to learn.

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    Quote Originally Posted by Deeper Cheaper View Post
    Thanks Dan. The pumps were serviced along with everything else about 15 hours ago. The Rinda scanner, is this something most all you guys have in order to work on these engines? Is this the best route or should I just go to my mercury mechanic?

    Thanks Sydwayz!
    Best thing to do is split the cost with a neighbor or buddy, or three, and you guys can share it as needed.

    They don't diagnose the engine for you, but they get you pretty close. If you have a $150 sensor/component that's the culprit of your alarm; and you have to wait for 3 1/2 weeks to get in to see your mechanic in the middle of summer boating season; yeah you are going to want that scanner to find out what you can on your own.
    Just the time and cost savings vs. 2-3X of hitching up the boat to drive it to the marina is worth the offset of having your own tool to start triage on your own. I keep mine on the boat, and I've used it on long trips, and loaned it to plenty of folks at events & group trips. Trust me on this one; not money wasted.

  7. #7
    PBN User 92nsx's Avatar
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    Get your self scanner or bring it in. Not to be a Dick but that is the only way, other wise you are just pissing into the wind. It is like asking why your check engine light is on in your truck. We wont know unless you scan the computer and see what the code is.

    You are hitting garden mode. Yes there are "common" things that can be wrong. First one comes to mind is water pressure by your description. New impeller/ pump so it could be bravoitus. Maybe you have no oil pressure or the computer thinks so.

    But again it is just pissing into the wind with out the fault code. So If you plan on doing your own wrenching it is the very first tool you buy in the marine world. Below is my 1st gen Rinda. I picked it up used off ebay 4-5 years ago when I bought my first Baja. IIRC pd $200 . (had to buy the ends tho $40 each) Now days they go for $400-$600 and have newer style out.

    1502920429856.jpg
    Last edited by 92nsx; 11-09-2017 at 08:05 AM.
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    So got it figured out. It ended up that my exhaust temps were too high and that the water pressure was low. Pulled the impeller and it was fine like I thought. What finally guided me to the issue was realizing that the engine ran fine if the water hose was connected to the flush line inside the engine compartment, but did not if the hose was put on the drive. The valve inside the T that is in the main water line from the transom to the sea pump was stuck causing a restriction. I pulled the T out and replaced it with just a T with no valve and everything seems to be just fine. Thanks for the help.
    BajaDan and 92nsx like this.

  9. #9
    PBN User 92nsx's Avatar
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    ^^^ Good catch. I'm putting that in the memory bank.

    Thank you for updating the thread

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    Quote Originally Posted by Deeper Cheaper View Post
    So got it figured out. It ended up that my exhaust temps were too high and that the water pressure was low. Pulled the impeller and it was fine like I thought. What finally guided me to the issue was realizing that the engine ran fine if the water hose was connected to the flush line inside the engine compartment, but did not if the hose was put on the drive. The valve inside the T that is in the main water line from the transom to the sea pump was stuck causing a restriction. I pulled the T out and replaced it with just a T with no valve and everything seems to be just fine. Thanks for the help.
    This is pretty common on the garbage system that Baja installed. That check ball is a point of failure as you found out. I've seen/heard of, quite a few that overheat like yours when above 45 mph, because the check ball setup is gummed up with debris restricting flow. You did the right thing by removing the spring loaded check ball system and pitching it.
    Last edited by Sydwayz; 11-29-2017 at 03:23 PM.

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