On Sun, 26 Jan 2020 16:37:40 +0000, mm0fmf wrote:

If you add fuel but not enough to cause the sender to move to the next
level, the range calculations will not know you have added more fuel so
the range wont increase but will keep decreasing as you drive. The range
will re-calculate at the next time the sender level changes, probably
upwards.

The fuel gauge on the dash will in all probability have no direct electrical
connection to the sender, instead it could be driven from an ECU output. The
dash computer may even just sniff a CANBus signal representing that fuel level,
interpret that and then drive a bargraph, a stepper motor or a moving coil
device with a pointer on the end.

The actual level from the fuel tank sender might be digitised to 8 bits or 256
levels, or even more, so the possibility of putting say a litre of fuel in a
tank holding 60 litres and the actual level measured by the ECU not changing is
pretty small.

But the gauge itself might only be driven to one of only say sixteen discrete
levels. In the past they were heavily damped, now that is effectively done in
software.

The initial range after refuel is calculated from the actual measured fuel level
and the rate of usage from immediately before the refuel, and updated with the
actual usage when the engine starts. If you coast down hill for many miles
before refuelling your range can be drastically overstated.

Similarly if you dispense small amounts (maybe 3 litres) of fuel from a can into
the tank, the range instantly updates on an ignition on event without the
vehicle starting and turning a wheel, even after it has been sat unused for
several months.

But as ever your specific vehicle range measurement techniques can vary.

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