Can I clarify something please?
Under normal circumstances with everything working as it should and turning the ignition on the fuel pump can be heard to run then stop.
Is that because the ECU stops it from pumping or is there an internal pressure switch in the pump that temporarily switches the pump off?

If the latter and connecting 12 volts to the pump then that pressure would need to collapse back through the pump before any further 12 volt supply would have any consequence.

Secondly if you have changed parts associated with the ECU dont these need to be programmed to match other components in the car as illustrated in one of the other topics and posted by “pscan”?

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