Originally Posted By: itguy08
Originally Posted By: rodinator1234
HPFP are cam driven fixed displacement piston pumps that are feed by a electric fuel pump. They can not adjust volume of fuel. For example, E85 has 2/3 the energy of E10, therefore the HPFP would have to be able to deliver 2/3 more fuel at the maximum fuel demand rate to maintain enough fuel pressure and volume to provide enough fuel to maintain the AFR. And it simply can’t. Usually HPFP have a 30% over volume design, that’s it.
Ford's HPFP can vary both the volume and pressure of the fuel.
Ford HPFP
What
Quote:
The high-pressure system consists of a high-pressure fuel pump that is mechanical and driven by a special four-point camshaft lobe that is only for pump operation. The plunger action of the high-pressure pump boosts fuel pressure up to 2,150 psi. The high-pressure fuel is in the metal line leaving the pump to the rails as well as the fuel rails. There is also no return line in the high-pressure system. The high-pressure pump mounts on the left valve cover. Pressure in the high-pressure system swings widely with rpm and demand. Pressures here will swing from as low as 1,000 psi to 2,150 psi depending on conditions. Pressure is controlled by balancing the volume through the pump and into the rail versus the volume passing through the injectors. One complete revolution of the camshaft produces four strokes of the high-pressure pump. At maximum, these four strokes equal 1 cc of fuel delivered to the rail. If met with a dead end, that 1 cc of fuel would raise the rail pressure by about 800 psi. The injector cycling will vent that fuel into the cylinders at around 21 cc per second. The PCM raises and lowers the high-side fuel pressure by pulsing the fuel inlet valve (solenoid) on the side of the pump. The inlet valve controls not only the amount of fuel that enters the pump chamber, but also the amount that bleeds back into the low-pressure system when the pump’s plunger pushes the fuel out. The more the pump is filled, and the less that bleeds back into the low side, the higher the pressure will be in the rails. The PCM monitors a fuel rail pressure sensor to determine the needed action at the volume regulator. The pressure sensor is mounted to the top of the left-hand rail.
I've personally witnessed (via Torque and and OBD scanner) the pressure cycles of the HPFP pump.
As to why no Flex Fuel Ecoboosts - no idea. Probably lots of engineering for near 0 benefit. In the right hands the EB's are capable of great power.
What you witness is the fuel pressure regulator varying pressure in the rail based on demand. Fixed volume pumps driven by cams vary only in RPM the regulator manages pressure. Injector, pulse width, duty cycle and fuel load demand all calculate into the required fuel demand for performance and emessions compliance which is also a huge consideration.