Hi All

I've changed fuel pump( the one inside tank) two weeks ago and is down again. What can cause it? Wasn't me to change it last time so i cannot tell if fuel filter was ok. You can still hear the pump working but just not passing the petrol through. Car is 2001 1.8 in petrol
Duratec. Now the car dont want to start at all but before revs in idle has been up and down all the times. Lack of power when warm and need to switch the engine every couple miles