REFLECTOR: FUEL PRESSURE PUZZLE

[Tom Martino]

Something is happening that I can't figure out.   My engine (IO-540)
runs great ... but the fuel pressure reading (EFIS One w/ resistive
sender) goes down as I increase power.  In fact, at 2700 RPM ... fuel
pressure reads "0".  Obviously, I was getting pressure because the
engine was running perfectly, but the reading was zero.
 As I decrease power, the fuel pressure goes back up to normal (28 -
30).
I thought it was simply an instrument error ... BUT ... when I turn on
the "boost" pump ... during the low readings ... the pressure reading
goes back up to normal.  Turn the boost pump off and it goes down to
zero.  So, the gauge is reading the Boost Pump but NOT the mechanical
pump.
What would cause my pressure reading to go down at higher power settings
in an almost linear fashion?
By the way ... I checked the fuel venting and cleaned the fuel filter.
Everything is good on that end.
Where do I begin?
Tom
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