I have faced exactly same issue in last month. Had to change fuel pump twice. I have Vitz 2005 1000cc. There is a specific pattern or symptoms before it fails. But sometimes you can drive around whole day and suddenly pump fails.
- Long self when starting.
- Sometimes need second self to start.
- When you move the car from rest, it gives a gap in throttle. As if car loses power for 1/4 of a second.
- When leaving a signal on green. It feels as if car has no power for a second.
- Unstable car performance and excessive knocking.
Original fuel pump is quite costly so you must be replacing kabli motors. They are hit and miss. But what worries me is fuel pump is one of the most durable parts in a car. May be you need to buy the whole assembly. My old pump worked around 2.5 years.
One thing I can separate is I used STP Injector cleaner. May be a coincidence but I did use it before my pump failed and after that I used it again since it improves car stability and again pump failed.