Odd Fuel Gauge Issue

[DennisG01]

I'm stumped. My mother's boat - a 2000 192 with a 2000 Yamaha 150 OX66 - has a weird fuel level issue. The boat has the standard, (2) round Yamaha gauges. I can get pics later. But I spent over an hour yesterday trying to figure out the problem and it should have taken 10 minutes. I am absolutley stumped as the fuel level "system" is about as dirt simple as dirt simple gets... and I left the boat yesterday worse off than when I started!

EDIT: Just to clarify, this is NOT a "fuel management" gauge - no GPH function. Fuel and speedo, along with time and battery voltage at the bottom.

-- First, nothing has been messed with - she's had the boat for 5 years and I'm the only one that works on this boat. So there's no Previous Owner Syndrome to worry about Everything has been working just fine for 5 years.

Issue: At the gauge: one bar is blinking.

-- I tested the level sender... it's good "KUS" style (straight rod)
-- There is a pink and green wire (boat side wiring) at the sender, connected to the senders' white and black wires.
-- I verified that the green wire has good continuity to ground
-- I temporarily hooked up a new sender - no change
-- I connected both the green wire and the pink wire together - no change (fuel gauge does NOT read full - it continues to show one bar blinking)

OK, so that means the issue is either the pink wire on it's way to the gauge or the gauge, itself, right?

BUT... here's what's throwing me for a loop...

-- When I temporarily connect the boat side pink/green together at the tank...
---- With the battery switch OFF and the key switch in the OFF position... the main gauge (not the fuel gauge) will turn ON
---- With the battery switch OFF and the key switch in the ON position... the main gauge will turn OFF.

Whisky Tango Foxtrot?

 

[loubeer]

I may not be understanding your problem, but how much fuel is in the tank? When the fuel level gets real low, it is normal for the last bar showing to begin to blink.

 

[SkunkBoat]

BUT... here's what's throwing me for a loop...

-- When I temporarily connect the boat side pink/green together at the tank...
---- With the battery switch OFF and the key switch in the OFF position... the main gauge (not the fuel gauge) will turn ON
---- With the battery switch OFF and the key switch in the ON position... the main gauge will turn OFF.

Whisky Tango Foxtrot?

without fleshing it out completely, I think it has something to do with a "ground" (more specifially a neg 12V return)

possibly the gauges are getting their ground thru the fuel sensor instead of directly to the neg 12V terminal

Turning on the key is putting 12V on the sender. if you tie them together you put that on the green wire.
I have seen odd things with fuel gauges when a "ground"(not necesarily the sender ground) is off or corroded

I would try jumping a wire from the gauge ground to the neg terminal or even all the way back to the battery.

good luck.

 

[enfish]

without fleshing it out completely, I think it has something to do with a "ground" (more specifially a neg 12V return)

possibly the gauges are getting their ground thru the fuel sensor instead of directly to the neg 12V terminal

Turning on the key is putting 12V on the sender. if you tie them together you put that on the green wire.
I have seen odd things with fuel gauges when a "ground"(not necesarily the sender ground) is off or corroded

I would try jumping a wire from the gauge ground to the neg terminal or even all the way back to the battery.

good luck.

I agree with this assessment. Almost every whiskey tango foxtrot electrical issue I've encountered that makes no sense is from electrons finding a path to ground they shouldn't be taking... (well, actually positrons since electrons flow from ground to +voltage, but I digress...). There's likely a bad ground connection somewhere, just got to find it. Good luck!

 

[SkunkBoat]

(well, actually positrons since electrons flow from ground to +voltage, but I digress...)

We called them "holes" back in the day....

 

[seasick]

Remove the pink wire at the sender and connect it to a good ground, Gauge should read full.
Disconnect pink wire at the sender and leave it hanging. Gauge should read empty.
If that is the case, the gauge and signal wiring are OK.
If that tests out OK, reconnect the pink wire to the sender terminal. If gauge flashes one bar, it thinks the tank is almost empty. If the tank is not almost empty, either the ground at the sender is bad
or the sender is bad
As alluded to, the ground reference for the gauge is the gauge ground. If the gauge self tests OK, it's ground is probably good but the tank ground could be bad. To test, run a wire from the sender groung to a good ground, preferablt a negative terminal of a battery. If the gauge now works correctly, the tank ground or sender wiring fir ground has a problem'
BTW, is the tank plastic?

 

[DennisG01]

Thanks, guys. Yes, I did all the normal tests (see above for a better description. Yes, plastic tank.

I did see an old ground that was broken off on the backside of the gauge on it's "bracket". But I didn't find a hanign wire anywhere close by to match up. I'll check again - and/or run a temporary ground to that spot just to double check.

 

[seasick]

Is there a ground wire connected to the sender in addition to the pink signal wire?
There should be and that wire needs to go to house ground.

 

[DennisG01]

Is there a ground wire connected to the sender in addition to the pink signal wire?
There should be and that wire needs to go to house ground.

Yes, correct.

-- There is a pink and green wire (boat side wiring) at the sender, connected to the senders' white and black wires.
-- I verified that the green wire has good continuity to ground