yamaha fuel management gauge

[mark]

MPH(from tach),GPH, synch ,gallons consumed all work ok but mpg gives me all kinds of incorrect readings. I think that it gets mpg from simply
dividing mph by gph. I figure it must be a malfunctioning circuit in the gauge. Any ideas??

[boats.net]

If you are using the Yamaha speedometer connected to fuel management gauge make sure it is reading correctly, a restricted speedo pickup in lower unit will affect speed and fuel use readings. There is calibration switch's on back of fuel management gauge; you can make corrections of +3% to -4%.

[mark]

Thanks for the input. I am using the input from the Yamaha speedometer and that is reading correctly. The adjustment of the fuel management gauge won't help because I'm getting crazy mpg numbers like 350 mpg (I wish!!)26 mpg, 55 mpg, etc. It just jumps around all over the place. That's why I think that its the fuel management gauge itself and will return it to Yamaha under
warranty but I want to exhaust any other fixes before I do. Any ideas ?

[jb123]

bad grounds on it ???