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Fuel gauge problem on AQ145a

I

isisthree

Member
Hi, I have a small problem with my fuel gauge. I wonder if anyone can give me a clue as to where to start.

The gauge intermittently goes hard over to the "full" position when turning the ignition on, and will then occasionally go to show a correct reading.

Do you think it is a problem with the earth, the gauge or the sender unit.

Any advice would be greatly appreciated as I am not electrically minded
and don't know where to look first.

Many Thanks
 
Last edited:
Take the sender wire off. Touch it to ground(earth) and look at the gauge. It should go full scale. Do this several times and if it goes full scale every time the gauge is good and you're looking at the sender as the culprit.
 
Hi, Sorry for not replying earlier but only just been to the boat today.

I took the wire from the sender and the gauge still went to full scale. I put a meter acros the sender wires and they read 7.4volts. The guy in the auto shop says that there must be a restrictor in the system, but according to the manufacture of the boat, Fairline, they say they never built any boats with restricors.

There are 2 wires coming from the sender. Should they be earth and live or both live?

Any help or suggestions would be appreciated as I am even more confused.

Thanks
 
Your next step should be to eliminate the gauge. Disconnect the sender wire from the gauge (should be pink) and see if the gauge returns to zero. If not the gauge is faulty. If it does you almost certainly have a short to earth between the gauge and the sender. The sender creates a resistance between the gauge and earth dependant on level, therefore one of the wires should be connected to the pink back to the gauge and the other should be connected to earth.

Bill
 
Bill , Thanks very much. I did as you said and with the live wire off the gauge, it still went to the full scale, so it must be the gauge.

AS a further test I measured the voltage on the sensor when I started and it was 3.2v. I then added about 9 gallons of petrol and the voltage went to 4.2v so I guessed that the float had moved and altered the resistance. By the way its a 100 gallon tank so I did not expect it to move that much but at least the voltage went up.

Thanks again for the advive

Regards

Nick
 
Nick

Don't rush out and buy a gauge yet. If your voltage INCREASED across the sender as you added more fuel then you don't have a USA instrument but a VDO. The following resistance charts are for each type.

USA

empty 240 ohms
half 103 ohms
full 33 ohms

VDO

empty 10 ohms
half 85 ohms
full 180 ohms

They react differently to an open circuit sender, the USA type will go to zero, the VDO will go full scale.

To make 100% sure, disconnect your sender wire from the gauge as before, you said the gauge went to full scale. Now take a piece of wire and connect the sender lug on the back of the gauge to earth (battery negative). If the gauge drops to zero then it is VDO and your problem is being caused by either a bad joint in the cable between the gauge and the sender or a break in the wire somewhere which is intermittently making and breaking. If you prove that you have a VDO, connect a temporary wire between the sender and the gauge to see if this cures your problem

Regards
Bill
 
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