There are 3 hoses to the "T" shaped regulator. 2 are across the top of
the "T" and these are the regulated lines from each head's injectors.
The other line is where the excess fuel and pressure is released back to
the fuel tank. This is known as the return line. If you hook up the
pressure gauge and watch it while you pinch the return line closed you
can tell if the low pressure problem is with the regulator or
elsewhere.This pinching prevents the regulator from working and lets you
see what pressure the fuel pump could make by itself.  If the pressure
shoots up with the return line pinched then the low pressure problem is
with the regulator. If it does not, then the fuel pump may be at fault
as the pump should be able to greatly exceed the nominal regulated pressure.

The pinch test only tells something about the regulator when the
pressure is truly below the regulator's spec. Even a properly working
regulator will show a pressure rise with the return line pinched. We are
only checking to see what is causing a known low fuel pressure issue.
Of course this assumes that your pressure gauge is reasonably accurate.

Mark

Craig Oda wrote:

>....
>My fuel pressure is about 23-24psi at idle when the engine is hot.
>This is 5 to 6 psi lower than the pressure recommended in the Bentley
>manual.  Is this the fuel pressure regulator?  I've got a spare fuel
>pressure regulator from a _used_ engine that I can swap in tomorrow to
>see if it will help.  Of course, I'm not sure if the used regulator is
>good or not....
>
>