Yamaha F115 voltage issues

[Cosmo2233]

Hi all - Hopefully there are still some experts around in the sea of spam posts that might have some guidance for me

Engine - 2003 Yamaha F115

When I fire up the engine cold the motor voltage reads 12.8 to 13.2 volts and stays there. I am under the impression that idle voltage should be around 14.2 volts or so. The boat will get on plane just fine and has no problem maintaining 14.4 to 14.6 volts when above 2,500 rpms or so. Sometimes when returning to idle I will see the voltage drop to low 12's or high 11's and the motor will sputter, misfire, and die out. Fires right up afterwards. I did checks on the stator, pulser coils, and rectifier and they seem to be functioning.

I noticed that when I unplug the water temperature sensor at idle, the engine will increase both rpms slightly and voltage will increase to 14.4v, the engine will generally sound stronger. The water temperature sensor, and the air temperature sensor both read 4.73 volts (unplugged) when the ECU is awake (engine not started). The TPS sensor reads 4.99 volts.

Can anyone explain to me why motor voltage will increase when the water temperature sensor is unplugged? Also would this sensor robbing the voltage from the motor be enough to cause a misfire and stall out sometimes when returning to idle?

Thanks all

[gtreanto]

Boy this place is quiet now. How is your battery? Marine/Automotive systems rely on the battery for balance and maintaining a constant voltage. The RR will use the battery as it's reference point. I would expect lower voltage output from the RR at lower RPMs. I would check a shop manual or google to find the operating range of your sensors. Also you could buy a new sensor and check its resistance and compare. Not sure if electrical is your stalling issue. I have twin F115's and my port will stall occasionally when I throttle down. I've had a dealer look at it and they balanced the engines but it still happens. I just restart the engine and be on my way.