Piper Arrow electric fuel-pump

wrote:

Aside from wearing the pump out prematurely, there's nothing significant about
running it for long periods of time. Of course, if you left it on indefinately, you'd
get no indication about one of the pumps failing.

I had a similar experience in my Cherokee 180 on the right tank. About 400'
AGL after takeoff on the right tank, the engine sputtered to a stop. No fuel
pressure, and the boost pump was already on. Switching to the left tank fired it back
up. Took about 3 seconds to diagnose, act on, and get the engine running again, but
felt like 3 hours. I had noticed a drop in fuel pressure at high flow conditions
(full rich takeoff) on the right tank before that time but didn't think much of it.
After that incident, we tore into the fuel system and found a paper wasps' nest in the
right tank fuel line after removing the tank. I'd suggest any discrepancy like that
to be looked into and the problem found.

Yeah.. I'm sure it's an obstruction, but at the moment I'm a lonnnnng way away
from any reasonably equiped repair shop.

Also, just as a data-point. The Cherokee (not sure about the later Arrows)
line has an extremely *marginal* electric boost pump stock. We ended up installing
the Petersen autofuel STC on our plane which requires replacing the stock pump with
two (only one at a time) replacement pumps. Rather than pumping around the engine
pump, they can (individually) pump through it now. Before the upgrade, I never saw
much difference between the pump being on or off. Now, in full-power climbout, I see
5 psi with either boost pump, or about 2 psi when I turn them off. According to
Petersen, the fuel pump swaps were necessary when the stock pump, "failed to meet
miniumum flow requirements." A euphamistic way to say Piper's original design sucked
and wouldn't pass ceritification requirements today.

It may be just my combination of equipment, but with the electric pump on, the
fuel pressure stays fairly stable, but the engine-driven pump has never given
a constant reading, it fluctuates from minimum to about mid range on the gauge.

MC wrote:
: It may be just my combination of equipment, but with the electric pump on, the
: fuel pressure stays fairly stable, but the engine-driven pump has never given
: a constant reading, it fluctuates from minimum to about mid range on the gauge.

At different power settings/attitudes, right? Fuel pressure gets awfully low
on mine if I turn off the electric pump in a full power/rich power-on stall
attitude... probably 1psi. As I said befo marginal.

-Cory

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Hi All:

If we're talking about the Facet "beer can" style pump, the pump can be left on
indefinitely. (Have taken one apart. Nothing to them.) There's no heat
limitation. Depending on your plumbing (parallel or series), it might affect
your mixture very slightly in flight. (Carburetor.)

The right tank problem could be due to deteriorating fuel / vent lines in the
wing. Light Plane Maintenance did an article on pulling the tanks and
replacing these hoses. They're rubber hoses with a life limit and the usual
breakdown deterioration. You're looking at a tedious job. (If you can get a
337, I'd replace with a longer life hose. Maybe an AQP style.)

Aircraft Spruce sells Facet replacement pumps.

At different power settings/attitudes, right? Fuel pressure gets awfully
low on mine if I turn off the electric pump in a full power/rich power-on
stall attitude... probably 1psi. As I said befo marginal.

Cory's problem is probably endemic to the Piper vent system. I suspect, during
the stall attitude, you're pulling a slight vacuum on the vents.

On our Glasair, we had similar low pressures in climb attitude. Turns out the
vents didn't protrude far enough below the wing. I extended the vent tubes
another inch and a half, and that solved the low pressure on climb out problem.

Hope this helps,

Mike Palmer
Excellence in Ergonomics