ibjman wrote:
Finally, one has to realize that pressure is created only by restriction somewhere down the line from the pump.......in this case the fuel pressure regulator behind the throttle body assys. in the return line from the fuel rail back to the tank.
OOPS....
This is true that the pressure is created by restriction, but....
The main restriction is done at the pressure regulator
on the pump (pressure relief valve #1).
The pump generates 65PSI pressure, and then the pressure regulator behind the throttle body assy drops it down to the usable 36PSI.
Here is a simple explanation on how a pressure relief valve is working:
The small hole in the pressure chamber (#2) communicate with the seat of the valve. When the pressure is high enough to overcome the spring pressure, the ball is lifted from the seat and the pressure is relieved by allowing the pressurised fuel to flow back to the tank. At that time, there is no or little restriction, the pressure drops down near to zero and the valve closes and starts to rebuild pressure again.
This is a really quick action and this is why the valve on the return line in the tank (first generation of K100) has the tendency to rattle.
If you have very small particles of contaminant lodged between the ball and the seat (most of the time rubber), a leak is created and the pump may not be able to build enough fuel pressure to overcome the spring pressure, the contaminant will stay pinched between the ball and the seat for ever.
The only option is to dismantle the pump and blow the hole at 80 or 100psi.