Hey Bill. A whole bunch of tests you can do without flying. I'd sure
encourage that. Highly unlikely it's a fuel pump unless you routinely
operate them without fuel. As Jeff suggests, fuel is important pump
lubricant, should resist urge to run sys dry.
If you shared pics, it would help. Particularly gascolator, pump,
plumbing.
Since you get consistent good results from turning on second pump, that
points to flow restriction as likely cause. So a good test would be to
undo fitting at engine and pump fuel into bucket. Measure volume with ruler
and stopwatch. Pump 1, pump 2. This will also disprove pump theory. You
could repeat test by disconnecting fuel return line. This is more severe
test as now pump has to achieve 40 psi. Bad pump would not flow much volume
at 40 psi.
Methodically go thru sys looking for debris, kink. Not just gascolator,
but other areas too. It's possible to have gascolator leak air and lean
sys.
For that matter, you may have engine running lean due to intake leak
(other?), 2nd pump adds touch more fuel per injector pulse. Thus masking
true cause. So I'd do the propane test (or other) for intake leak. Something
loosen during flight and allow leak. Poke and push on components. Review o2
sensor values. By chance do you record these things during flight? Do you
have other data that can prove it was or was not lean?
Verify each pump has independent grounds, power supply. Verify sys
voltage. Recalibrate fuel pressure sender.
We have natural tendency to say "aha, I bet that's it". Forgetting that
there are some simple tests to prove it. This is important time to be
conservative and methodical.
Good luck.
-al wick
----- Original Message -----
Sent: Monday, May 27, 2013 7:09
AM
Subject: [FlyRotary] Intermittent fuel
pressure loss
Has anyone had an instance of intermittent failure of the
fuel pumps? A
couple of days ago the engine started to
intermittently lose power and
changed tanks. (both tanks were low,
about 5 gal in right and 10 or so in
left) The problem stopped so
I thought I had unported the right tank.
Several minutes later it
started again on the left tank and I turned on the
other fuel
pump. That seemed to stop it again. I still suspected that
I
had unported the tanks.
A couple of days later, I took off
with about 45 gal and after about a 30
min flight, the engine lost
power again twice. I turned the other fuel pump
on and the
problem stopped.
My fuel system goes thru a Gascolator then to the
two pumps, then to a fuel
filter. I assume that the Gascolator or
the fuel filter could be getting
clogged, but I don't think that the
other pump would bring the pressure back
if that were the case. I
only have about 70 flight hours on the pump and
maybe about 100 hours
total including ground runs.
Also on the flight back, I had both
pumps on and showing 40 lbs of pressure.
I then turned the secondary
pump off and the pressure held at 40 lbs. This
strikes me that it
is an intermittent pump failure. I plan to clean the
Gascolator,
replace the fuel filter, and replace the pump.
Any thoughts,
suggestions, experiences?
My wife was with me on
the last incident and I don't think she is interested
in trying to join
Ed's glider club!
Bill B
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