[Vwdiesel] Er nope I'm still not convinced (pump-pressure-wise

[Mark Shepherd]

H'mm are we talking about the same thing? Are you talking about the orifices that leak off the excess fuel at the end of each stroke (the amount of which is controlled by the sleeve to change volume injected)...
Here's my take on pump operation ....
Vane pump in  VE pump sucks/lifts fuel out of tank.
The vane pump pressurises the bulk of the interior of the VE  pump. 
The pressure is limited by a recirculation valve Val mentions that is up near the vane pump. 
This background pressure which you say is perhaps 100psi is used to flood the high pressure chamber in front of the injector piston; which 4 times per revolution squeezes fuel up to the 155 bar which then squirts down one of the 4 exit points through check valves and out along the injector lines. 
The amount injected is regulated by a sleeve which is positioned to cover to a greater or lesser degree, holes in the piston chamber which alows the overspill of the fixed amount of fuel in the chamber.
At the top of the pump above the high pressure exits but still in the 100psi reservoir is the exit for the excess fuel that has been lifted by the vane pump. This has to return back to the tank.
 If the exit was too big then (although all pump fuel wont drain out as its near the top of the reservoir) the body of fuel will  flow into the high pressure chamber only[mainly] due to vaccuum rather than being assisted by the 100 psi. So chamber may not fill fully.
The hollow banjo bolt has the 'pin hole' in it that maintains the minimum general fuel pressure (and some believe helps to heat returning fuel) 
Does your extended bolt have this same hole in it? How accurate is it?
This is why I feel your measurments will only be comparative and may need callibratiing against a perfect pump.
I wonder if this small hole wears and drops pump internal pressure? 
Perhaps this affects injection linearly and not just at the extremes...


 
Mark (The Miser)Uk 
"There's nothing more stimulating than driving past a bonfire and then realising it's your car that's smokin"

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