Yamaha digital guage help needed.

[Hollywoodfish]

I have twin 150 HPDI's (2001). Here is my guage set-up. 2 Tachs, Speedo (Mainly used for Batt & Fuel level), and Fuel Managment.



The fuel managment guage is the one giving me a problem. The Synch does not work (it used to). The fuel burn is not correct (total and actual). I filled the tank and fished for two days, the total burn read 54 Gals and then I pumped 90 in. While cruising it shows actual burn anywhere from 5 ish to 12 ish, but it should be more like 20 something ish. I am not sure if it is the guage, a wire, or some other issue. How can I diagose the guage? Will 6Y8-83500-11-00 be compatible with my set-up? Also, will this guage tie in W/ GPS for speed? My current speed always reads 4 on the guage.

What is my next step? I don't really feel like forking out a few hundred bucks for a guage to only find out that was not the problem. Thanks

[rodbolt]

carefully check all the wiring between the fuel flow senders and the FMM.
use the ohms function on you DVM ,should see less than 1 ohm pin to pin.
yes you can use a GPS input on the FMM. the speedo is water pressure operated so I imagine your pitot tube is clogged.