Charles:

Good reply for Farshid.

I would also like to wonder at what kind of current the fuel sensor is capable of handling. Maybe his strange problem with the fuel readings relates to some type of resistive element heating someplace in the circuit.

On the older car meter systems I have looked at the fuel guage is a simple mechanism with a bi-metal strip that is connected to the meter needle through a clever little linkage. This moves the meter needle in proportion to the bend in the bi-metal strip. A thermal resistance wire is wound around this b-metal strip so that current through the resistance wire heats the bi-metal strip and causes it to bend. In the system I investigated this winding resistor is connected to +Battery and then in series with the variable resistance of the float sensor in the fuel tank and then to ground. (I do not recall if the +BATT was applied at the tank end or at the meter end).

These systems were designed to handle a certain amount of current and maybe the net 60 ohms feed from +5V that Farshid is using is too much current as compared to the original meter circuit. This could cause heating in the variable resistance on the tank sensor making the settling time be long after his board powers up.

Michael Karas