trip computer faliling it's math test - faulty mpg readings

[Shellcase]

Hello all,
So my phase1's mileage calculator is all wrong, when i floor it it says 11l per 100 km, and when i let go, it says 30l per 100 km.
common sense made me think that perhaps there's a fuel flow sensor that's wired the wrong way arround, but since you guys probably took your cars apart a 100 times already, maybe you can point me to the right direction?
*this also causes the fuel light to come on when there's a quarter of tank still in it.

Thanks,
Danny

 

[Goodj]

Is it reading in l/km or mpg.

Because those sound more like MPG figures

 

[Shellcase]

it's is definetly liters per 100km
i live in Israel, we use the metric system here, honestly, i'm not even sure that there's an option to convert the reading.
maybe need to connect a laptop and play with the settings?

 

[Goodj]

You can change what it reads on the display. In UK the default is MPG but press the wrong buttons enough times and it switches to l/km.

That said, it also says on the display what it's calculating at. So if it says on the display it's doing l/km then I'm fresh out of ideas

 

[Shellcase]

it does say l/100km
question is - how does it calculate the numbers, where it gets it's info?