fuel pressure regulator

[dn]

> 

>         I don't understand your explaination of the fuel regulator in part 1.
> You state that by plumbing the regulator to the intake manifold, as manifold
> pressure rises, it biases the regulator in order to keep a steady 45 PSI.  
> 
> I always thought that by plumbing it to the intake manifold, you effectively
> allow manifold pressure to effect change into the regulator pressure. So, in
> effect, as engine loading increases, and manifold pressure increases, a corr-
> esponding increase in fuel pressure results.  What's the deal?


To butt in here-

The  fuel  pressure reg has the BACK side of the diaphragm (the spring
side) tied into manifold pressure.  It's easier to think in  terms  of
ABSOLUTE pressure rather than GAGE pressure.  By example, suppose that
the regulator  is  set  for  50  PSI.  When the engine is at idle, the
manifold absolute pressure is near zero, which has no  effect  on  the
regulator.   Fuel  pressure (and pressure across the injector) is thus
at 50 PSI absolute.  As manifold pressure increases when you open  the
throttle  (less engine vacuum), it has the effect of boosting the fuel
pressure because the manifold pressure is opposing the spring  in  the
regulator  thus  decreasing  the  effective force on the diaphragm and
opening up the regulator.  Suppose again, that at half  throttle,  the
manifold pressure  is  now 7 psi... this adds to the regulator setting
and results in an absolute  fuel  pressure  of  57  PSI.    Since  the
manifold  side of the injector is at manifold pressure, you still have
a net result of 57-7=50 PSI  across  the  injector  itself,  thus  the
regulator maintains  a  constant  pressure  ACROSS the injector.  Fuel
rail pressure, however, varies with manifold pressure.

In the real world, it's  not  quite  this  straightforward,  but  this
explanation is close enough.  Hope this clears it up for ya.

regards
dn


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