I have twin '05 496 mags. Both start and run great.
At 4000 RPM port engine sounds hard alarm and enters guardian mode. Guages and fluid levels are fine. I have to throttle back to idle for the alarm to shut off, then everything is fine as long as I stay under 4000 RPM. If the water impeller was a problem, I think the alarm would go off before 4000 RPM.

you will really need to have a scan done to pinpoint the alarm.

If you wanted to, remove and swap the seawater pressure sensor from the non alarm motor to the alarm motor to see if that is causing the alarm. That was the case for me.

Did you change or upgrade anything?? Like exhaust? Jamie / Lakeside


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No uprades or changes. Might have to break out some money for the scaner, or find a local guy who wants to make a couple extra bucks with his scaner.

I changed the fuel filters, and ran the boats again. This time when running I throttled up a little at a time, all the way up to 4700 rpm (wide open) and no problem! When I start from a idle, off plane, and gun it, the hard alarm sounds at about 4000 RPM, just as the boat is starting to plane. What sensors will cause the computer to go in guardian mode?

Try cam sensors, and drive sensors. I just went through a similar situation. Starboard motor shuts off. It wiill start right back. Fuel pump issue. Fuel peassure was low System goes into guardian mode, but the sensos will record a failure data on the computers. See my posts on sim. issues with other threads. Good luck.

Any final answers on this one, I am seeing a simliar problem on friends 496 with exhaust work.

Nearly impossible to say anything definitive without having it scanned. The Rinda is $500 worth it's weight in gold. I suggest going in with a few friends to share one.

If I were to "guess" I'd say water pressure sensor has debris in it or the impeller is failing. I had same issue on my 496, replace impeller 3 fliping times, and also change the impeller housing. Finally I changed the sensor. Once I got the new sensor installed I tapped the old sensor on the the floor and a few grains of sand fell out of it.....

For 350 bucks and your laptop you can view everything at once, even data log. Save your self a lot of time and aggravation, not to mention wasted money buying sensors based on a guess.

http://mefiburn.com/sc/details.asp?item=mefi5scan