|
The reason for the check valve in the outboard pump configuration is to keep the heat buildup in the line between the pump and rail from vaporizing the fuel after the motor is shut off after a hot day's running, forcing the liquid back into the tank and leaving nothing but vapor under pressure for the positive displacement pump to work against. This is vapor lock, if one can get one's mind off of the carbureted version and the myth that EFI eliminates it.
With the pump in the tank, and usually submerged or at least surrounded by a large volume of liquid, the high pressure tank pump is not prone to the same vapor lock the external pump is.
The notion that the 1 second pump run at key on (in some systems) is there to speed up starting or prime the line is, in my opinion, a faulty notion. As you say, even with an entirely empty line and rail, the pressure is up before the first two revs cranking, and if normally filled, well before one rev.
Really, the reason the Bosch external pump is so expensive, beside the fact it is made like a brick house, is it is an antique. Violates all planned obsolescence goals.
--
Art Benstein near Baltimore
Mom's Law: The most expensive part you replaced was the root cause and true culprit when you explain it to Mama.
|
