Wandering Yamaha Fuel Gauge

[Dhirsh]

I noticed after replacing all my batteries that my fuel gauge seems to wander up and down from full to about 1/3. Totally random and highly inaccurate. I know exactly how much fuel I have because I reset the logs every time I fuel and the fuel burn on the Yamaha gauge isn’t affected . Was going to chalk it up to a bad sender but it just seems too coincidental that I’m noticing this after replacing all 4 batteries and the charger. Any thoughts before I dig the sender out and inspect/replace?

 

[SkunkBoat]

Make sure your House negative and other negative bus connections are connected well and both tanks are connected well to the negative bus
Because of the way a fuel sensor circiut works, a bad "ground" problem can effect the reading. You might even notice say that turning on electronics makes the fuel reading go down.
I had a similar problem. I had been working on the batteries and left the house ground wire off. Fuel tank readings on the yamaha gauge were erratic. Electronics were getting ground(sort of) through the tank ground. The more I turned on the worse it got until of course at some point nothing worked..

 

[Dhirsh]

Good advice. I’ll bet I missed a ground. That’s exactly what it’s doing. I’ll check this weekend. Thank you !

 

[seasick]

It would help to know what the actual level should be when the gouge swings from full to 1/3. If there is a bad ground, the level will be low or empty. Note that the sender may be grounded to the tank and tank will have a wire that grounds it. So check you connections and make sure that you didn't miss a common ground cable that ties two batteries together.

 

[Dhirsh]

My fresh water tank has been pegged at zero since I bought it. I‘ll check that too. That tank is plastic so I assume the sender has to be grounded elsewhere?

 

[seasick]

My fresh water tank has been pegged at zero since I bought it. I‘ll check that too. That tank is plastic so I assume the sender has to be grounded elsewhere?

Yes the sender needs a ground. To check the gouge, run a good ground wire to the sender terminal that connects to the gauge. The gauge should read full. If that works, move the test ground wire to the ground terminal of the sender. If the gouge reads something other than empty (and the tank has some water in it) the sender ground wiring is bad. . If grounding the wire to the gauge works and grounding the sender ground terminal doesn't, the sender is bad or maybe stuck in the empty position. ( All this assumes a typical mechanical sender with a float and not an electronic type)

 

[Dhirsh]

Yes the sender needs a ground. To check the gouge, run a good ground wire to the sender terminal that connects to the gauge. The gauge should read full. If that works, move the test ground wire to the ground terminal of the sender. If the gouge reads something other than empty (and the tank has some water in it) the sender ground wiring is bad. . If grounding the wire to the gauge works and grounding the sender ground terminal doesn't, the sender is bad or maybe stuck in the empty position. ( All this assumes a typical mechanical sender with a float and not an electronic type)

Thank you,
Found the problem with the fuel Sender and a few other things as well. When I replaced my batteries I missed one ground connection that went from Bank one to bank two. Jumper cable end got buried behind a battery and I missed it. Most problems instantly solved but feel a little foolish. I still replaced the end on the tank ground at the battery. It was definitely sketchy and may have also been bad?Still have to diagnose the water tank gauge but will use your method on that the next time I’m on the boat. Thank you for the spot on advise.

 

[seasick]

I have missed that cable myself as have many folks.Don't feel foolish. Now if you make that mistake twice and don't realize what the problem is, then you should feel foolish