On 26/01/2020 15:57, ARW wrote:
On 26/01/2020 15:39, Clive Arthur wrote:
I put some petrol in the car today , not much about 10 litres.

It didn't seem to register on the gauge, that's a bargraph with
limited resolution but even so that was strange.Â* Stranger still was
that the 'miles to go' figure didn't change either, it stayed on about
90 miles.

I've never seen that before but I usually put more in, albeit
infrequently, it's not used much.Â* The only difference today was that
I parked at the pump on the 'wrong' side because the garage was busy,
and wasn't close enough to get the nozzle in fully and it was upside
down. The petrol did go in the car and not on my feet.

I had assumed that the fuel gauge was a float on an arm jobbie, but
maybe it's more complicated.Â* Any ideas?

It's an 04 Citroen Xsara Picasso.


I am interested.

The hire van that I used to move a piano never altered the fuel gauge or
the "miles to go" range on the dash despite shoving 4 gallons of fuel
into it from fuel cans.

The range/mpg will be computed from the mileometer and fuel used. The
fuel used is calculated by the ECU by how many injections and how big
they were. So as you drive it knows how far and how much fuel used. It
can then use that for mpg. Remaining range is updated as it knows how
much it had and how much is being used.

The initial range comes from how much in the tank and how much is used.
i.e. tank reads full, car sets max possible range from known last mpg.
As you drive, fuel use is calculated and mpg/range updated. Next time
level changes, i.e. sender indicated next level, 9/10ths full, range is
re-evaluated based on current mpg and known remaining fuel.

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.