Fuel gauge and mpg gauge problem

[LagunaE30]

ok, so as the title reads my fuel gauge and mpg gauge are playing up.
when i bought the car both of these worked perfectly, the fuel pump went wrong so i changed that, around a month after that the fuel gauge started jumping around crazily, one minute it would be at empty the next at full, so i tightened the nut at the back of the gauge to no avail.
i then changed the sender unit under the rear left passenger seat, this was a working unit from a friends car, the gauge now just sits under the red marker and does not move at all.luckily the reserve light will still come on.
The mpg gauge still works but unlike before it sometimes get stuck at the 30mpg mark, stays there for a few seconds and then returns back to normal.
any help will be appreciated
thanks
fozz

[LagunaE30]

any1?

[danbear]

my fuel gauge does excatly the same. I'm going to sort this out after my other problems lol