I was only guessing that it acts as a check valve to maintain
fuel rail pressure after shutdown, to improve hot starts by
preventing fuel
vaporization in the rail.
Yes, I forgot to mention that function.
If you look at each FPR, you will see that fuel flows FROM
the fitting
on the side, TO the fitting at the rear, in each instance. It flows
from the fuel pump into the side of the A Bank FPR and
through the rear
fitting to the fuel rail. Fuel flows from the left fuel rail to the
side fitting of the B Bank FPR, and through the rear FPR
fitting to the
tank return line.
So, they both act to regulate downstream pressure?
I fail to see how the A Bank FPR can act like a damper or
modulator to
affect inlet pressure at the rail. My guess would be that it
opens at a
lower pressure than the B Bank FPR.
A more constant up stream pressure reduces the required
modulation in the rail. To see how this can translate to
better regulation in the rail, you have to consider how
pressure regulators work. In general, pressure regulators (at least of
the
kind I’m familiar with) never really maintain constant pressure.
The reason is there has to be some change in pressure to cause
movement of shaft that controls the flow area at the seat. If
the upstream pressure varies a lot, the second regulator has to
move a lot, meaning that the rail pressure has to change a lot
to effect the required change in flow area. Some here will this as
proportional control.
The two FPR’s DO have different
part numbers and have different rear fittings according to the Parts
Catalogue.
I suspect they are different parts because of mounting differences,
and as you point out, different set points.
And the B Bank FPR should NOT be always open to some degree
as someone
suggested, or there will be no maintenance of rail pressure after
shutdown. It is a spring-operated (vacuum modulated) valve
that doesn’t
open until rail pressure is attained.
Perhaps they meant during engine operation.
Ed Sowell
1976 XJ-S
http://www.efsowell.us/ed/myJag.html
// please trim quoted text to context only