You need to check the vents are ok. I’d do that before changing the pump. If the vents are the problem then a new pump is a waste. The inward whoosh is the big clue. The tank is effectively sealed with no mechanism to allow air in to fill the void as petrol is removed.
As an analogy, get a plastic pop bottle. It feels solid when full. Release the top. Whoosh! The CO2 is released. It has stayed in the pop due to the pressure in the clear space below the cap reaching equilibrium and no more is released from the liquid. Now, when the pop has all gone place your lips round the open top and suck. The bottle will collapse. Punch a hole in the cap and the bottle never feels solid as the CO2 just vents out.
This is roughly what happens in a fuel tank UNLESS there is a vent/valve to manage the pressure changes.
Last edited by sospan; 29/08/22 12:50 PM.
