Date: 29-03-24  Time: 01:42 am

Author Topic: Fuel gauge gone wierd  (Read 718 times)

nitemare

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Fuel gauge gone wierd
« on: 01 July 2019, 09:34:11 am »
I took the bike out for a ride yesterday after a long break. I noticed on the way back the fuel gauge shot up to to over FULL and the orange fuel light cam on  :eek . This seemed worse on the fast roads and dropped to normal-ish when I was in the 30's.


I would have said the fuel gauge was stuck but the orange light worries me. I have done nearly 100 miles off the full tank so should be around a quarter to a half full.

I should add that the bike seems to be revving okay...

Any ideas? And how easy is it to sort?
« Last Edit: 01 July 2019, 10:37:01 am by nitemare »
Never underestimate the power of human stupidity, especially when you're out riding.

bandit

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Re: Fuel gauge gone wierd
« Reply #1 on: 01 July 2019, 11:21:27 am »
Similar issues have been posted before, check electrical connectors under tank & also wiring/connections clocks & headlight area.  Smile

His Dudeness

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Re: Fuel gauge gone wierd
« Reply #2 on: 01 July 2019, 07:40:44 pm »
I think you have a short between the three wires going to the tank. Disconnect the connector going to the tank. Does the fuel light go out and the gauge drop to E when the connector is disconnected? If it does it means the short is between the connector and the tank. If the fuel light stays on and the gauge stays past full the short is on the loom side of the connector.

How the fuel gauge works is there's a float in the tank. The float is connected to a variable resistor. When the fuel level is high the float is at it's highest position and the variable resistor is at it's lowest value of resistance so more current flows through gauge so the needle moves towards the full mark on the gauge. If you bypassed the variable resistor completely with a short to ground the gauge would read even higher than full like yours is doing.

The fuel light is a bulb in series with a thermistor. How that works is when the fuel is covering the thermistor the heat that the thermistor generates is transferred into the fuel. That keeps the thermistor cool which causes the thermistor to have high resistance so most of the voltage is dropped across the thermistor and not much across the bulb. As the fuel level drops below the thermistor, the thermistor heats up because now the fuel isn't cooling it. As it heats up it's resistance drops so now less voltage is dropped across the thermistor so more is dropped across the bulb and eventually it gets to a point where the bulb has enough voltage drop across it to light. If you had a short to ground and bypassed the thermistor the bulb would be on all the time no matter what the level of the fuel is, like yours is.

So I think the three wires are joined together causing a short.

nitemare

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Re: Fuel gauge gone wierd
« Reply #3 on: 02 July 2019, 10:13:22 am »
Thanks I will take a look at the connector to the tank. Might be at the weekend, will let you know if I sort it.
Never underestimate the power of human stupidity, especially when you're out riding.