We know a fuel pump cannot pump a gas vapor. That was back in the carb days when the fuel pumps were within the carb. Engine heat evaporated the fuel, the pump couldn’t pump the vapor. Hence vapor lock.
Move on to the V12s and hard starting…many cases which we called “vapor lock”. EXCEPT…the fuel pump is in the tank…submerged in fuel. The fuel in the tank is liquid. It SHOULD be able to be pumped to the rail, thru the injectors and into the engine. So, why are these engines prone ? to hard starting after being run and heated?
I think it’s PRESSURE in the fuel rail from fuel vapors. The fuel vaporizes in the rail from engine heat, the vapors expand, the expansion increases internal rail pressure, and that rail pressure is greater than pump pressure…or A bank regulator. I think the ID of the fuel hose sizes ( on the injectors) and the rail ID size is so small that it doesn’t take much vaporization to create a large pressure increase. A pressure that is greater than not dead head pump pressure but the A bank pressure regulator…3 Bar.
Hence a long cranking time. The opening/closing times for a combination of 12 injectors…operating at milliseconds .starts the decline in rail vapor pressure as each injector opens, until the vapor pressure is reduced (purged) to less that the A bank regulator and liquid fuel begins to flow into the rail and injectors.
Maybe a member schooled in fluid mechanics could chime in here.
SD Faircloth www.jaguarfuelinjectorservice.com