[Diy_efi] pressure vs flow?

[Tlsalt at aol.com]

Brian Michalk wrote,

 I would like to know various flow rates per pressure.

Also, I understand they open at 30psi(depending on part number), but am
confused as to operating pressure.  When they reference operating pressure,
is that the regulated pressure from the FPR to the CIS regulator?  Or is
that the pressure at the injector?

Hello Brian,

CIS does not control flow at the injector with a pressure regulator. The 
injectors receive "system " pressure which is regulated to a consistent 
pressure by a regulator in the fuel distributor. The amount of fuel delivered 
to the injector is controlled by the height of the slits in the control 
plunger.  This is mechanically connected to the airflow sensor plate. The 
height that the airflow sensor plate moves in relation to a given volume of 
air is altered by varying "control pressure" (separate circuit of fuel that 
does not reach the injectors).

I would guess that the pressure the injectors actually sees is slightly 
different from the "system" pressure because of the varying restriction 
presented by the height of the slit in the control plunger. However, Bosch 
does not calibrate off the injector pressure.  The "system" pressure is 
fixed, and the "control" pressure varies to alter the mixture for 
compensation (cold running, acceleration, boost mixture). Reducing 
the"control" pressure allows the air flow sensor plate to rise more for a 
given volume of air, exposing more of the slits and increase the volume of 
fuel delivered to the injector. Think of the airflow sensor as a "see-saw", 
as more air enters the system, one side rises, causing the other side to 
fall, exposing an increasingly larger opening to the injector fuel lines. The 
basic relationship is fixed, the "control" pressure loop just changes the 
weight balance of the "see-saw".  When control pressure is low (cold engine)  
there is a 40 lbs kid on the air flow side, as the engine warms up, the kid 
slowly puts on weight until he hits 100lbs (2.5times). KE and Lambda CIS 
alter a third pressure differential to slightly tweek the fuel delivery 
volume, but not by altering injector pressure directly.

Bosch was actually quite surprised that it worked. The best part is 90 psi at 
the injector and that little pressure driven, wobbly pin atomizing the fuel.

Paul Saltwick


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