Good job, Steve! I have added this to BAC as an FAQ.

Keep in mind that these "pressure gauges", like the "fuel flow"

gauge on the Sierra or CSP-equipped planes, are not measuring

primary fuel pump pressure. They are measuring the pressure in

the flow divider, or "spider", on top of the engine, which delivers

the fuel to the fuel injection lines. This is metered fuel that has

passed through the Bendix fuel servo; not fuel from the fuel pump

to the servo. That's why the "pressure" reads so low at idle; there

is very little fuel flow at idle, therefore very low pressure in the

spider. The gauge simply shows that fuel is being sent from the

servo into the engine, while enabling some other diagnostics as

described by Steve.


From: []
On Behalf Of ke4oh
Sent: Monday, January 23, 2006 7:36 AM
Subject: [musketeermail] Re: A23-24 Fuel PressureGauge

The fuel pressure gauge has only limited usefullness. It will rise
and fall with changes in RPM and mixture.

It's main use is to tell you something is wrong. If the pressure
begins to drop below what is "normal" for the flight regime you are
in, it is telling you that there is a fuel starvation problem. That
would be a tank running dry, fuel valve positioned off or in between
tank detents, or a failing fuel pump. If the pressure reads higher
than "normal" for the flight regime you are in, it usually indicates
a clogged injector.

As to what readings are "normal" for different flight regimes, you
will have to fly for awhile and determine that for yourself. These
things aren't really calibrated such that the readings on your plane
would be the same as on my plane all operating conditions being
equal. FWIW, mine barely registers anything at idle, about 8 on full
power full rich climb-out, and somewhere +/- 5 at 65% cruise power.
But as I said, it varies with RPM, altitude, and leaning. My Super
has a fixed pitch prop. A CS prop would induce additional effects on
the "normal" readings.

Best regards,

Steve Robertson
N4732J 1967 Super III

--- In, "huntmlh" <huntmlh@y...> wrote:
> Cheers all, Just started to fly an A23-24 200hp Musketeer. Can
> someone shed some light on the fuel pressure guage. What should a
> normal indication look like, what is the most prevalent use fo the
> fuel pressure gauge, and other comments anyone might have? Thanks.
> huntmlh

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