Fuel gauge

[SirMichael]

I have a 1988 Hunter 28.5. Fuel gauge on it is intermittent. It worked for a while and showed about three quarters of a tank when was full but now it's just showing empty.

I measure the voltage at both the fuel gauge and at the sending unit down on top of the fuel tank. But I'm not getting anything at either place.

I haven't been able to trace the wiring back, and I can't seem to find a wiring diagram. It was pretty hot down in the stowage locker where the tank is located so I didn't spend a lot of time digging into the wiring.

I'm pretty good at electronics so I'm trying to figure out what to do to fix this thing but I'd like to have something of a schematic on the fuel gauge system. I did manage to find schematic showing the Yanmar 2GM20 engine wiring but that does not include the fuel system.

Any suggestions?

Mike

 

[Warren Milberg]

If you are referring to the fuel gauge on top of the fuel tank in the starboard lazarette, I believe it has no electronics running it but rather is a simple float type gauge. On my boat, I never pay attention to it in any event. My "fuel gauge" is No. 2 pencil and pad. I simply start with a full fuel tank (11.5 gals) keep track of the engine hours and I know the 2GM20F burn rate. Much more accurate than the gauge.

 

[Capt jgw]

Fuel gauge wiring is pretty simple. The tank itself is grounded, usually via a terminal on the perimeter of the sender. Then the sense wire from the center of the sender to the "S" terminal on the gauge. Then the positive and ground terminals on the gauge. Loose or corroded connections on any of those could be at fault. If there's no voltage at the gauge the problem must be in the positive or ground wires to the gauge, and those are probably connected to the instrument panel somehow. There will never be voltage at the tank (at least you hope not, that would be bad). The gauge might not have been installed by the factory so the wiring could be substandard.
If the gauge was incorrect when it was working, that could indicate a poor connection on the tank ground or sense wire, but on the other hand they are notoriously inaccurate so that might have been the best it could do.

 

[SirMichael]

Thanks for the reply, I did some more digging on generic fuel gauge wiring and I see what you mean that the voltage is just applied to the meter in the low side of the meter goes to the fuel tank. Should be pretty straightforward. There would have to be some voltage at the fuel sending unit, but I'm sure there's a high resistance in the meter to keep the current potential down.

I'm hoping to make a trip to the boat either today or tomorrow to work on it.
Mike

 

[SirMichael]

Well I managed to fix the fuel gauge, turned out to be easier than I thought. The fuse holder had made a very poor contact to the fuse. There was no voltage at the gauge because of the fuse. I tried cleaning up the contacts on the fuse & holder with the brass brush but I couldn't get a good connection. So I just built my own fuse holder using a couple of female spade lugs (see attached picture). I do need to replace the fuse with something smaller, 5 amps is a bit large for this application.

Turns out I have nearly a full tank of fuel!
Thanks for the moral support guys!
Mike

 

[HMT2]

Sir Michael,

Very clever work around on the fuse holder! I'll have to remember that trick!

 

[Stu Jackson]

Very clever work around on the fuse holder!

Agreed ^^^^^^^^^^^^ Well done!

I have the straight glass fuses, but have some of those on board anyway, good trick to know.