No MPG readings

[Fishbones]

For the life of me I can not get the MPG funtion to work on my LMS 400 gauges.I have the Lowrance GPS puck dedicated just for the system because I am running Furuno navigation equiptment. I have a 2007 DF200 engine, I even changed out the interface cable with the newer style square plug and made an adapter to fit the round plug on the engine. The system is set for ground speed. I get gallons per hour, speed and fuel used but it just flashes 0's on mpg. WTF? Any other ideas?

[boats.net]

It may have to be ran several miles before a canculation will emerge.