Mercruiser low voltage indication

Rusty Owner/Technician Oakham, Massachusetts Posted   Latest  

I have a 2012 SeaRay 310 Sundancer HID#SERT4123A212 that has twin Mercruiser Mag 350s with Bravo drives, Axius system, Vessel View & DTS. I'm bothered by a .5 to 1 V lower-than-actual voltage indication on the starboard gauge and Vessel View. I have confirmed with a Fluke DVOM that the starboard battery voltages at KOEO and running are normal (12.6/14) The starboard system powers the “house” and the voltages at the house fuse panel are normal. I've poked around on the engine and found normal voltages but the instrumentation shows ½ to 1 V low most times. It seems after an hour or so of run time, the error is minimal.

I have Diacom and the displayed (battery voltage) data agrees with my instruments so I'm assuming one module is reporting incorrect voltage. What I'd like to know is which node derives battery voltage and on what pin/circuit so I can measure it at that point. Daicom shows “system voltage” accurately and it agrees with what I measure and what we'd expect but the starboard “battery voltage” is wrongish. On the Diacom screenshot you can see that at KOEO, system voltage is 12.8 but battery voltage is 12.1

I have Googled some EWDs for engine ECUs but I have no way of knowing if they are correct for mine and (again) I have no idea if battery voltage is bussed from the engine ECU or another. 

ESN#2A014627

preciate any direction. 

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Your Rustyness: I don't have a tool here to verify on your application but I'll give you something to be thoughtful about. In newer multi-engine setups, the connection between the two engines can be terminating or combined (I forget the technical term for the latter). The terminating variety uses terminating resistors like a CAN setup. The other one does not. On these types of applications, the…

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Rusty Owner/Technician
Oakham, Massachusetts
Rusty Default
 

Thanks for your thoughts. I'm getting nowhere looking for helpful answers or decent diagnostic info to this point. I'm thinking the circuit in question might be the ECU KAM Power so my plan (when I go back to the boat) is to unplug that ECU and look for B+ on the plug and then load it. Maybe I'll see a significant drop.

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Rusty, On my boat I ended up getting the Mercruiser Shop Manuals on PDF from the internet. I don't have the correct files for your boat, or I'd send them to you. I also have the Diacom program and I was a little underwhelmed with that, but you can load the PDF files and open the manuals from the Diacom program. Another thought would be to go to your SeaRay dealer and see if one of techs…

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Rusty Owner/Technician
Oakham, Massachusetts
Rusty Default
 

I watched a tech run the Diacom on my boat some time ago to try and determine which of the 4 O2 sensors was misbehaving and, like you, I wasn't impressed. I called Rinda Technologies and was advised that the tech was likely using "Generic" OBD-M. I bought the OE Specific connector and SW and I'm quite happy with its abilities. The S/I section however is empty so I need to see if that's a…

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