Fuel reserve sensor

[KDIMD]

Can the fuel reserve sensor in the tank get loose or out of placement? Reason I ask is that last time the reserve kicked in (or rather bike started to die), I switched to reserve and stopped for gas. But only able to pump in 7-8 liters. Meaning the tank was still half full. Reserve should kick in at 3 liters (0.8 gallons).

Is there anyway to adjust without having to remove the tank?

 

[davesax36]

It's possible that it's gone bad, but I haven't heard of that too often. If you drain the tank you can remove it from the bottom without removing the tank.

 

[KDIMD]

Thanks, Looks like it be pretty simple to swap out and not that expensive. Just not sure if the original has gone bad or not.

Anything else that would get the fuel reserve to kick in early?

 

[Redbone]

I had one that was broken which the low fuel warning did not work at all (sensor element was broken) I swapped it with a known working unit which resolved the issue. I had the tank empty when I changed it but it was easily done, and I have a braced swingarm and Marks 4 into 2 exhaust which has a crossover pipe. It is ~$65 to replace the sensor/ gasket with new @ boats.net.

 

[one2dmax]

I have good used sensors if needed. You can shine a flashlight in there to see if the wire is broken.

Changing with aftermarket exhaust isn't terrible but changing with stock exhaust is much more difficult.

 

[KDIMD]

I checked under the tank, the wires are in good shape and no corrosion. Actually look pretty good. I check the resistance and I get 850 ohms in a 90 degree garage.

I was reading this sticky below and it mentions that temperature has a lot to do with when the fuel reserve light goes on.

I live in the Philippines where average temperature is in low 90s. Plus I have a 4-2-1 pipe that does not have any heat shielding. I have noticed that the fuel light comes on when I have half a tank and start to run into traffic, which in turn raises the temp in my tank. The range states that the resistance should be at 700-1100.

Anyone have any ideal whether the excess heat is causing my fuel light to come on early? If so, is there anyway to insulate the tank bottom from the exhaust?

XXXXXXXXXXXX

Q: “How does the low fuel warning light work?”
A: The low fuel level sensor unit in the V-max fuel tank is a solid-state thermistor device. That means it has NO moving parts, N0 float and NO contact switch. Many other brands of bike use this type of sensor.

A thermistor is a semi-conducting material that allows current to flow when it is warm i.e. does not resist the flow of electrical current when it is warm but will resist the flow of electrical current when it is cool. A thermistor is best thought of as a slow switch.

The sensor uses the fuel in the tank as a heat sink. When the fuel level is over the sensor it is cooled by the fuel, becomes less conductive and prevents the input voltage from completing an efficient circuit to the electrical ground connection. This keeps the warning light off.

When the fuel level is below the sensor the surrounding air is not an efficient heat sink so the thermistor warms up and allows current to flow. This turns the warning light on.

So when the resistance in the circuit is high the fuel in the tank is above the low fuel level and when resistance in the circuit is low the fuel in the tank is below the low fuel level.

The resistance value for an unsubmerged fuel level sensor is 900 ohms +/- 200 ohms @ 20 degrees Celsius or 68 degrees Fahrenheit.

Q: “Why do some people seem to be able to go much further on their reserve supply and others just barely make it to the next fuel pump?”
A: The fuel level sensor is a temperature and voltage dependent resistor.

Variations in temperature, the quality of the electrical connections and the power available to the circuit will all affect its ability to complete a circuit to the warning light.

Here are some examples.

Example One – Temperature effects resistance.

It’s summer and your motor is hot, your aftermarket pipes have done away with the heat shield between the tank and the rear headers. This has warmed the fuel in the tank and so it is no longer an efficient heat sink for the thermistor in the fuel level sensor. Warm fuel will allow electrical current to flow through the circuit more readily than cold fuel so the low fuel warning light may come on early. In this case you would have (relatively) more fuel in the reserve supply. However, when a cold, wintery, wind chill is cooling the tank the low fuel light might come on at a relatively lower fuel level.

The low fuel warning light on the V-max will vary with temperature of the fuel heat sink.