It is not good for pump!
If you put 1 or 2 liters to fuel tank its may be not enough, it need more...
Once I have the same problem, my pump after working whithout fuel did not start. I have checked all electrical fuel part - it was ok. Then I have put +12V to the pump from battery by separate cable and after 20-30seconds it begin to work(then I turn out that cable). I think my pump was obstructed.