Check Valve Operation:
The electric fuel pump outlet contains a one-way check valve to prevent fuel flow back into the tank and to maintain fuel supply line pressure (engine warm) when the pump is not operational. It is also used to keep the fuel supply line full of gasoline the when pump is not operational. After the vehicle has cooled down, fuel pressure may drop to 0 psi (cold fluid contracts), but liquid gasoline will remain in the fuel supply line between the check valve and fuel injectors. Fuel pressure that has dropped to 0 psi on a cooled down vehicle (engine OFF) is a normal condition. When the electric fuel pump is activated, fuel pressure should immediately (1-2 seconds) rise to specification.
Abnormally long periods of cranking to restart a hot engine that has been shut down for a short period of time may be caused by:
- Fuel pressure bleeding past a fuel injector (s).
- Fuel pressure bleeding past the check valve in the fuel pump module.
- A defective fuel filter/pressure regulator.
You need to mount a fuel pressure gauge to the fuel rail temporarily and test
for residual pressure .Your car should hold 3 BAR about 45 lbs for at least 20
minutes after shut off. If it fails to do this the liquid fuel in the fuel rails
may boil and on restart the vapors being injected are not sufficient to light
the fire . Pumping the accelerator on a fuel injected car does little more than
amuse your foot as you wave the throttle butterfly in the wind. The time spent
doing that may allow the vapors to purge and liquid fuel to fill the fuel rails
and be injected. The check valve , all 8 injectors or the fuel pressure
regulator could be leaking off the pressure.
You have already checked the two fuel dampers so they would not be at fault plus they would leak all the time causing running issues. So check the residual pressure.