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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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