These threads are why I return to OSO a few times a week to learn some of the fixes that I might hae to attend to in the future . Nice one guys..

A 100% rule of thumb is with computer control engines and current diagnostic equipment that tests running available power. if your in depth scan shows 100% available power, this will verify that engine guardian is not responsible for reduction in RPMs.

The ECM / PCM system monitors the sensors on the engine, if a malfunction is found the computer system stores a fault, depending on the fault, available power may be reduced as the engine guardian will be activated.

At what point does the warning buzzer sound? At the onset of power reduction or just before? (for rev limiter)

Does not having the trim limit switch hooked up to the boat cause low rpm ? I have a whipple 496 that will not run past 5100 rpm seems to fall on its face at 5000 my scan tool does not show reduced power . Does the computer net to see the trim limit switch?

rev limiter shuts down spark. persay rev limit really has nothing to do with warning horn but it does with overspeed fault. this can set codes along with warning horns - the overspeeds will show in the scan but the warning horn will stop once rpm's are back in specs.

Warning horns come into play as soon as the computer detects a sensor out of range and or out of spec. basically it warns the persons that a malfunction has taken place and will not protect the engine. as some warning horns are critical so protecting the engine is up to the end user. again as soon the ECM / PCM detects an out of range spec / malfunction the warning horn will sound. Its that fast.

Marine engine manu's list continuous warning horn as a critical fault. Engine damage can take place if continue running.

post 14 more info is needed do you DTS, Do you have smartcraft gauges and of course serial # of your engine. Again all serial #'s determines what you actually have as far as an engine set up including parts that has changed during engine serial # breaks. A 2001 496 is totally different set up compared to 2010 496 just as a 2006 496 is different as well, even mid year engines can have changes incorp into them plus different parts installed. It all goes off of serial #'s, not persay year of boat.

Heres is a prime example is at a certain engine serial # breask even the engine harness was changed from a 10 pin to a 14 pin connector, other things change as well thru serial breaks, ignition coils, fuel set up, emission related parts, fuel filters no shift switch / then a shift switch, even the belt tensioner changed at a certain serial # break and so on.

I have a single 525. I am running without a tach now. When I am running light and in real good conditions I can hit 85+ but I usually reach a point where I get a constant buzzer. I drop the drive a bit to lower the RPMs and the buzzer stops. Oil and engine temps are good. Water flow is good. I don't see how it could be anything but an over rev warning buzzer. People tell me that my boat sounds like it is really revving. You can hear it in this short, crappy video. In normal operating conditions I cannot reach these RPMs and top speed is usually around 83. I am running with the original 496 harness for now. Are you saying that the warning buzzer cannot be due to the RPMs? BTW this video was around 83 and I did not get the buzzer.
https://www.youtube.com/watch?v=kSUWplf6m6A

I do not have smart craft gauges zand I don't know the ser. # it had a whipple on it when I bought it so the cover was gone that had the ser# on it , The boat is a 2004 288 sunsation it has a custom tune from Dustin

Its called overspeed and yes your bumping off the rev limiter. It will show up in a scan of the motor and show as many times as the warning horn has came on and off then back on again in a fault called overspeed. So yes you are hitting your rev limiter in which sets off a continuous warning horn until rpms are decreased..

Usually the rev limiter is set at a max of 150 rpm's over the suggested MAX rpm range from the OEM marine engine manu for stock motors. Your rpm range is 4800 - 5200 so if I remember correctly the rev limiter is set at 5350 or possible 5450 for your app. Anyways to long of a period of overspeed will put the motor in Guardian mode as a protection mode.

I would not keep bumping off the rev limiter for obvious reasons - hard on the valve train, too high rpms possible valve float but more important as many people do not realize is you are dropping ignition spark but the fuel is still being supplied to those cylinders.

Thank you. It is propped to hit the limiter only in perfect conditions. Usually it will not rev that high.