Mechanical pumps can easily be designed to put out a lot more than 6-8
psi. Think diesel injector pump. I don't think pressure had anything
to do with the move to electric fuel pumps. I don't know all the
reasons why the move was made, but I think it is simply better all
around to push the fuel rather than pull it and it would be very hard to
get a mechanically operated fuel pump back by the fuel tank!
I haven't seen a fuel injector yet that takes fuel direction from the
tank and injects it into the engine. The fuel needs to get from the
tank to the point of injection so there is still lots of fuel line that
can vapor lock if not under pressure or with sufficent flow. Fuel
injection doesn't change much with respect to vapor lock.
The way pressure regulation is performed with fuel injection, and an
electric in tank pump prevents vapor lock. The pump pumps fuel up to the
fuel rail. The pressure is regulated by a valve which opens and returns fuel
to the tank over a second line when the desired pressure is achieved. That,
and the fact that you are dealing with a pressurized line from the tank to
the fuel rail, rather than a line where you are trying to "suck" the fuel
from the tank to the intake of the pump. So... BOTH conditions you
mentioned - pressure and flow - are always present with fuel injection. Any
fuel vapor in the line when the vehicle is turned off is instantly
compressed into tiny bubbles as soon as the pump pressurizes the line when
the key is turned on. Those tiny bubbles will be swept through the fuel
rail, and into the return line when the pump restarts when the vehicle
If the system is functioning as designed, it cannot vapor lock. The system
should keep 20 to 25 psi in the line forever (until the line is opened).
You have a regulator and a fuel pump check valve that should prevent the
fuel pressure from going below that level.
Boy! I'm glad I ask about why do they put the Fuel Pump in the Gas Tank!I
became very interested in the fact it turned into an open forum of about
gassing your car!Now I can talk from experience and it is the best
teacher! Do Not Put the nozzle on automatic and get back into the car!
Leaving it to wash the W/S is bad enought!I have owned Sevice stations and
Later I hauled Gasoline to Service Stations and to the Farmers! Gasoline
does not make friends!I have seen countless failures of automatic nozzles!
It scares me the most when someone smokes while pumping the gas! My son was
caught on fire with gasoline, It burns fast and terribly! Just don't take
the chance PLEASE!!!!Now back to the original thing on vapor lock! I am
very familiar with vapor lock! can be cured on the older cars very easily.
It always ocurred between the fuel pump and carbureator due to the motor
heat va[porizing the gas in the line!About 2-3 clothes pins would act as
heat sinks and stop the problem-
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