Yamaha Fuel Mgt. Gauge issue

[L. Reed]

I am running twin 2001, 200 HPDIs, and my fuel management gauge is acting up. It used to give me everything but the MPG under economy, now it only gives me fuel flow / gallons used 20% of the time. It also does not show Port or Starboard, never did. Does this sound like a gauge issue or a sending unit issue? Neither one is cheap, don't want replace parts I don't have to.

Thank you

[boats.net]

Could be fuel flow sensors or a wiring problem, check that the wire connections at sensor are good and not corroded, check that Fuel management gauge is connected to both tach and to speedometer and speedo is working.

[L. Reed]

Spedo does work fine, I'll check the wires on the sensors, and make sure nothing has come loose from the back of the gauge.

[L. Reed]

OK, The wires & connection at both sensors look good for 9 years old, no corrosion, no broken wires. The fuel mgt. gauge IS connected to the Tach & Speedometer, and all those connections look great. Both the Tachs & Speedo work too. Can trash get in the sensors and cause them not to work?

[L. Reed]

Also was able to ge behind dash & check dip switches on FMG, everything set correctly.

[boats.net]

Probably is bad sensors, they do go bad more than the gauges do.

[L. Reed]

Probably is bad sensors, they do go bad more than the gauges do.

That's my guess, just wish there was a way to test them before shelling out $500.00 bucks.

[L. Reed]

Update. It looks like 9 years of E-10 fuel ate the paddle wheel inside the sensors. All is well now. Guess we just have to put up with the E-10 and all the damage it causes. Thanks for the input.

[Capt.Terry]

OLD post but similar issue if any one reads this, My fuel economy worked fine but now is working intermittently 2007 250 HP 4 Stroke Square gauge ? I am thinking this could also be my issue starting I have to locate this sensor, can one visually see this wheel ? on sensor if taken apart to inspect?

[fairdeal]

Your square gauge does not use a mechanical sensor- it gets fuel flow from the engine ECM.
but to calculate economy the gauge needs a speed input- that is what has been lost.

It may have been using a sensor under the cowling that converts the lower unit pitot pressure.
the pitot May be clogged, or the sensor clogged or kaput.
But if you run a GPS/Chartplotter with NMEA 0183 output, connecting the wires to use the GPS speed is / IMO - the best approach.