The reason your readings are not accurate is because as it stands the voltage drop across your fuel tank sender
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(variable resistor) will be 5 volts
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(if you're using the Dash 2 reference voltage) regardless, it is the only resistor in the circuit so all that changes with fuel level is the current flowing through it.
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On that note if you have simply wired it up like so:
Dash 2 5V reference
> fuel tank sender
> Dash 2 analogue input ![](./images/smilies/spacer.gif)
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it might be advisable to disconnect it, according to their website the maximum current flow on the reference output is 50mA,
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@3 Ohms
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(full tank) you will be pulling 1.67A!
https://www.race-technology.com/wiki/in ... FuelSender
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You need to add an additional resistor as Pauln mentioned
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(2 wire sender)
https://www.race-technology.com/wiki/in ... ensorToDL1
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this way as the resistance varies on the fuel sender so does the total circuit resistance, in turn the current flowing through the circuit will change and the volt drop across the added resistor will scale accordingly.
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Not wanting to teach you to suck eggs but here is the math based on the above link recommendation of adding a 1k ohm and using Paul's values of 3 Ohm
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(full) and 110 ohm
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(empty)
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V=IR
5=I*1003
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(total circuit resistance for a full tank)
5/1003=0.0045A
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0.0045*1000=
4.5V![](./images/smilies/spacer.gif)
this will be the analogue input voltage on a full tank
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5=I*1110
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(empty tank)
5/1110=0.004985
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0.004985*1000=
4.985V![](./images/smilies/spacer.gif)
voltage for an empty tank
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Edit: Just corrected the maths as calculated the volt drop across the sender itself and not the 1K load resistor!