General Fueling Question

[Haynesie]

Hey Everyone,

Had a general question pertaining to the fuel pumps in our cars. Are the pumps always pumping the same amount of fuel, or does the pump increase/decrease as vacuum/boost increases or decrease. Just curious as to how more fuel is sent to the injectors. I know the regulator dictates a lot of the process, just curious as to how the pressure goes up...if it is driven by the fuel pump increasing speed, or if it is driven by the regulator closing to prevent fuel from going back to the tank.

Thanks,
Jason

 

[mikestertwo]

They pretty much pump the same amount of fuel. The pressure regulator sends the excess back to the tank. The regulator controls the pressure in the fuel rail by monitoring manifold pressure. The excess goes back to the tank.

 

[ttribejr]

Layman terms:

they run full speed all the time -unless- you have a voltage booster that activates off something.

Some people run two fuel pumps and activate the second one off of a boost pressure switch (usually around 15psi)

as boost rises, your fuel pressure will rise on a ratio of 1:1. The reason is because the tip of the injector is now under pressure, so the fuel pressure needs to match that to fight against the boost pressure on the other side of the injector.

Likewise, when the car is in vacuum, the engine is "sucking on" the tip of the injector, so fuel pressure lowers to accommodate that.