Alarm at wake speed and goes silent when in neutral

[dalehegg]

I have a 284 Sunesata - Volva Penta 8.1L. Took it out yesterday and it ran great. Put it on plane at 3000 rpm no issue. When I slowed down to wake speed an alarm started and beeped every 3-5 seconds with no idea what it is. Engine temp, oil Press, depth all good.
When I placed in neutral alarm stopped. Also, hard to start. Like a rich fuel problem.
Any suggestions?

 

[dubs283]

Connect a scan tool to the ecm, only way to read engine data/faults

 

[alldodge]

Scanning is best way, the ECM will do this if a code is set.

 

[alldodge]

Could do some checks
Measure voltage at the battery with motor running, should is around 14+V
Use IR temp gun and see if exhaust manifolds or thermostat is getting to hot
See if you can get exactly 5V on one of the pins on the MAP or TPS