Help please! Fuel mileage gauge issue (mk2.5 Focus)

[Rob_F]

Hi Guys,

I'm not going to lie, I've joined here for some help; I'll be staying though!

I'm struggling at the moment with my 58 reg Focus 1.6 Zetec. 

The fuel mileage gauge (seems to be) reading incorrectly. Previously on a full tank I would be easily getting 340+ miles. Now I'd be lucky to reach 260, This is reflected on the mileage gauge on the digital dash. 

This is with the same style of driving, and same fuel. 

I'd much appreciate any ideas on this, as I'm a bit stumped... It seems as though something is going wrong but I'm just not getting the mileage out of it that I used to. 

Hopefully someone knows! Thanks!

[Micro]

Note your mileage, brim the tank, drive a fair distance, then brim the tank again. Work out how much fuel you have to put in the second time, and note your mileage from your odometer. You can calculate your MPG and figure out if your gauge is just out, or if your car is using more fuel.