Ok so yesterday was at lake cumberland and first thing I noticed in the morning when I launched my boat that my guardian alarm beeped twice when I put the boat in gear, in the meantime the boat was idling just fine butat the same time I noticed my tach bouncing between 1k and 3k (at idle).
So I figured I drug my boat all this way im going to see what happens, I opened the hatch and everything checked out.
Off we go and about every minute or so the alarm goes off but engines running fine, go through a no wake zone and started to open her up, eased her up to about 3500 rpms (according to my bouncing around tach) @40 mph and I got a long drawn out alarm and engine went to an idle as if I backed off the throttle but I didnt.
opened hatch again still no sign of any trouble.
after that the boat ran fine with no alarms the tach stayed steady the rest of the day and now im curious?

What happened?

Boat has a 496ho if that helps

No ideas?

Impossible to know for certain without scanning the motor. It will have the historic fault codes stored so you can reference them. That beep is akin to the Check Engine Light on your tow vehicle. It's and indicator, not really a troubleshooter.

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Best $500 you will spend your boat enabling you to enjoy your summer.

I suspect it is your Crankshaft Position Sensor though based on your tachometer acting up. Why I think such:
http://www.offshoreonly.com/forums/g...0-400-rpm.html

The Technical Q&A section may have some more information for you as well: http://www.offshoreonly.com/forums/general-q-20/

Some more good info on this thread on "beeps":
http://www.offshoreonly.com/forums/d...-2000-rpm.html

As a guess without eyes - hands - ears on your engine and no scan in which is needed to pin point your problem. IMO - IAC or TPS might be your problem. The TPS is not that common especially compared to the IAC.

If you able to reach your max RPM's, the engine is not in Guardian mode, also with a scan tool, you can look at available power, if it says 100% then you never were in any form of a Guardian mode.

On these Mercruiser ECM / PCM controlled engines it is always wise to carry a spare IAC. (cheap testing to see and cheap insurance). It is always a simple thing to change and might clear up your problem for the weekend out on the lake. Again this would be a guess to your problem especially without looking at any scan data & faults & history.

Thanks for the replies fellas, I think I will need to invest in one of those scan tools.