Fuel gauge reading too low, digital.

[Nobby the Bastard]

So, the strumpet's fuel gauge is reading too all of a sudden.. I don't think its a stuck or broken sender because it also says empty when it's still got a few litre of fuel in it.

I'm guessing that either the digital bit (lcd display plus low warning light) is miss reading the voltage or somewhere along the wiring resistance has increased due to a fault.

Has anyone else come across similar and what was the solution?
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[MCN]

A wide swing at it.

I would guess that the sender/float is probably easiest to replace.
It would be sweet if the easier bit to replace is also cheap-ish.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Nobby the Bastard]

[MCN]

'Traditionally' fuel level sensor systems measured current between the battery and the gauge with the sensor inbetween.
The sensor was a simple reostat (variable resistor).
Empty produced a high resistance and full provides zero resistance (effectively). The gauge was an ampmeter (Or voltmeter can't remember)
The simple test was to supply 12v direct to the gauge if it moved to full then it was ok.
Change the sensor.

More modern stuff maybe changes the physics. Some sensor systems use PWM (Pulse Wave Modulation) and are difficult for the uninformed to test. They almost always need at least three wires at the sensors.
The old stuff was Analogue and easy to test.
I don't know if any bikes use PMW.
I'd look on eBay for a sensor/float.

https://www.ebay.co.uk/itm/TRIUMPH-SPRINT-ST-1050-2004-2010-PETROL-FUEL-LEVEL-SENDER-USED-MOTORCYCLE/142997440633?hash=item214b4fc879:g:k7MAAOSwm4Zb2wWK
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Nobby the Bastard]

Two wires to the sensor. Its actually a rubber ring that floats in the petrol around a sensor tube and goes up and down witg the petrol level.

It should be as simple as you state to test, but because it's a solid rubber ring, i cant see how it can be floating lower than fuel level to record empty when its not. I can understand it getting stuck and reading low when it's full, though.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[andym]

I personally wouldn't see a low reading gauge as a major problem.... unless you run your tank to empty before filling up.

Fuel gauges are a luxury I've seldom had on bikes, so I just got into the habit of filling up after 100 miles and have found anywhere from 4 to 11 litres left in the tank.

[MCN]

It's using a more precise magnetic sensor. The rubber ring will be acting as a proximity switch.
The ring has a magnet in it that closes reed switches inside the tube.
That will energise sectors on the gauge to indicate level.
It's a suck it and see thing maybe.
You may be able to determine the sensors functioning by measuring resistance as you move the rubber ring on the tube.
I could be talking out the hole in my area too.

This shower of pricks sometimes post some usefulness.

https://www.triumphrat.net/sprint-forum/245554-1050-fuel-tank-connections-help.html#/topics/245554

(***Beware*** Heavily Polluted by Murican Motorcycle Tossers.)
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Hong Kong Phooey]

Have you had the tank off recently, pinched any wires or crushed terminals?
Checked output with multimeter?

It sounds earthy or wiry, chafing near the headstock happens on most bikes over time.

I don't have such luxuries as a fuel gauge, poor me has to reset the trip-o-meter every fill up.
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'81 CG125, '97 FZS600 : '99 CBR600F4, '09 KTM RC8

[WD Forte]

My theory guess

It uses a black pipe sender thing
Inside is a 'ladder' of changeover reed switches with resistors between them
dese fings

https://cdn-reichelt.de/bilder/web/xxl_ws/C300/MK23_90C2_01.png

As the magnetic float passes a switch it flips to the NO wire (signal)
and the combined resistance over the series resistors left in circuit
gives a voltage related to the fuel level.
the ECU read this volatage, translates it to fuel level and lights up
the appropriate leds

I reckon the sender is probably the bottom end of a voltage divider with a regulated voltage supply from the ECM.

If the magnetic float gets stuck or sticky , that will give erroneous readings

To test, you'd have to remove it and take resistance readings as you tip it upside down and back while watching the meter
I'd also read the voltage on the signal wire, if it's too low ( <5V)
that will give low fuel readings too.

Bad wiring and connections wil make it play up too
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bikers smell of wee

[doggone]

I think there's a connector under the tank sometimes gives trouble, could be damp in it, easy fix unless corroded if it is that.

[Nobby the Bastard]

I've not yet looked. I'm expecting it to be the sender but some of the readings don't respond to what you would expect.

I have a week off for crimbo so will investigate then. Tank hasn't been off since I fitted the scotoiler 3 years ago.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050