Quote:
Originally Posted by Doug007
Shiv,
Can you go into a bit more detail about how the amount of fuel fed to the HPFP is controlled?
The HPFP is an engine driven positive displacement pump, unlike the LPFP which is centrifugal and variable speed. Fuel is incompressible so the HPFP should be pumping an amount that is proportional to rpm (since it's engine driven) all the time. I don't really understand how a valve can affect the amount of fuel "gulped" by the HPFP.
Even if it reduces the pressure of the fuel, pressure has a negligible effect of fuel density so the HPFP would gulp the same amount that would only really change with engine speed.
Is the displacement of the HPFP pistons variable somehow? What am I missing?
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I had this same thought when I read part 1.
So, if the system regulates the input to the pump... seems bad. If it literally cuts the supply of fuel, the pump is pulling against a vacuum at high rpm, low load situations, (ie, coasting your speed down) or if the low side pump cannot supply enough fuel. To me, this seems like the root problem, not necessarily just a lowside fuel supply issue. It is a design flaw. The fuel supply issue could contribute, but even with a massive lowside supply pump, high rpm and low load would still do the pump in over time.
I am surprised that they do not circulate the excess fuel/pressure from after the hpfp pump back to the lowside supply. Running a pump with a dry input is bad. Especially if is force driven by the engine.
EDIT: I am kinda thinking what you are missing is causing the damage to the pump. Just my guess though and I could definitely be wrong.