I have a 2002 Searay 270 Sundeck with a 320 hp Mercruiser 6.2L
MPI/Bravo 3 Duoprop which has just developed an engine alarm problem.

After running 10 to 15 minutes at a cruising speed of about 3400 RPM,
the engine alarm sounds. Oil pressure, oil level, engine temperature
and outdrive lubrication levels all appear to be normal. The alarm
continues to sound until idling back and shifting into neurtral.

If I run below 3100 RPM the alarm does not go off.

I have checked the engine with a digital heat gun and can find no sign
of abnormal temperatures anywhere. The serpentine belt is properly
tightened and everything else seems normal in every way.

Does anyone have any suggestions on how to troubleshoot this problem ?

Is there any diagnostic equipment or process available to find out
exactly which sensor is being tripped ?