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Well On the Direct injection engines I am not sure how they are doing the fuel system. I was going to log into gm global connect and look but my buddy at GM ignores me most of the time so i cant go look for myself and get the info. Anyhow I am sure they are pumping it to another pump near the motor and then boosting that pressure. Similar to a diesel.
I honestly dont think it is as simple as ramping the voltage up to the pump or pumps.
After googleing it here is what the pdf file from GM has to say..
High-pressure engine-driven fuel pump for multiple injection events
To overcome the higher pressures inside the combustion chamber, as well as supply the
multiple injection points of the direct injection nozzles, an engine-driven high-pressure
pump supplies fuel to the injectors. This high-pressure pump feeds a high-strength fuel
rail that feeds a continuously variable pressure fuel rail attached to the injectors. The
high-pressure pump is supplied by a conventional fuel pump mounted in the fuel tank.
The high-pressure pump can supply up to 1,740 psi (120 bar) of pressure, although it is
dependent upon fuel demand by the engine. For example, at idle, the fuel system is
regulated to about 508 psi (35 bar) and increases with demand. The high-pressure pump
is mounted on the end of the cylinder head and is driven by the exhaust cam.
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