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That seems to be on the edge of FAA-recommended pressurized flow (1.5 X full power flow, IIRC), but I think that it's the pump SDS sells with all their a/c engine controllers, so it must work fine up to well over 200 hp. One thing Ross at SDS has ranted about is the quality (or lack thereof) of most mechanical regulators. Not sure whether poor regulation affects anything beyond tuning stability, though.
Charlie
Dave,
I have a filter just before pumps. The after pumps filter is on
top of the engine. Then a Y to primary and secondary fuel rail.
Pressure sender is at end of the secondary fuel rail.
In your installation it would seem that the regulator would
compensate for a clogging filter?
Anyhow, this is amazing pump info. I thought pumps would last for
thousands of hours.
Amazingly I now can't find the official flow rate specs for the
GSL414. Only the testing on https://vansairforce.net/community/showthread.php?t=168793
which gives about 42gph near 0 psi. The GSL393 is rated at 155lph
or 38gph.
The allure of the GSL414 is the three times lower current draw.
Seems a good way to monitor the state of the pump is to monitor
current draw. From my recent testing, looks like my pump is still
OK.
But the conclusion must be that the GSL414 is weaker and is likely
to hit end of useful life quicker than a GSL393?
I'll take a new look at possible air leak on input side as well as
better grounding.
Finn
On 5/23/2022 4:37 PM, David Leonard wdleonard@gmail.com wrote:
Finn,
Where is your fuel filter located? Mine in downstream of
the pump, but before the fuel injectors. Fuel pressure
gauge is just upstream of the filter for me, which I now
realize is sub optimal but does provide good info about the
state of the fuel filter. The pressure starts going up as the
filter clogs.
I also have a fuel flow sensor on my return fuel line,
which has turned out to be a great troubleshooting tool and
reflects the overall health of the fuel system.
I am using the walbro pumps that Tracy recommended. I
bought 10 of them once to have a supply on hand because I
never again want to delay replacing them when I see the
performance start to degrade. For me, the first sign would be
decreasing return flow. It more or less seems to linearly
decrease with the total time on the pump. For me, the
pressure starts dropping as the return flow gets closer to
zero. I have taken to replacing the pump earlier in the
process, like 50% reduction in return flow. With pumps like
the walbro, current demand to the pumps goes up as the flow
goes down. At some point the current demand will blow the
breaker and terminate the flight. I would guess that fuel
pumps seem to last 400 hrs or so. This is an improvement
since I installed a larger fuel filter to keep down the
pressure differential.
If your pumps are similar and your fuel pressure is
dropping at the injector, and the problem is not a clogging
fuel filter, then I suggest you replace the pump ASAP. They
seem fairly susceptible to damage from particulate
contamination or being run while dry.
Cheers,
Dave Leonard
Finn,
What
the fuel pump should be flowing and what it is flowing may
be two different things and needs to be evaluated before
being "comfortable" That is why I would encourage you to
measure the actual flow rate if you can do it safely.
When I left MS71 in May of 2017 following Charlie's rotary
fly-in, my 13B burned 18 gal/hr on
take-off and initial climb at 5800 RPM and
initial OAT of 80 degrees F. Your set-up likely would
require this much or more. This was the indication from a
Flowscan turbine type sensor which has been demonstrated
to be accurate. The flow measurement would just be a next
step in the investigation. If the flow rate is not what
is what it should be, then determining why would follow.
The replacement pump should be helpful in this regard.
If
you recover the fuel being bypassed by the regulator,
bubbles in that fuel will not necessarily indicate air
leaking into the fuel drawn into the pump. The process of
dropping the pressure when the returned fuel passes
through the regulator, causes dissolved air in the fuel to
separate. Bubbles in this flow will be obvious. If fuel
is drawn from a small reservoir (< a gallon or so) and
returned to that same reservoir where the bubbles are
allowed to escape to the surface, the bubbles will
eventually disappear as the fuel is degassed. Degassing
all the fuel from the wing tank is unlikely to occur due
to the large volume of fuel and the large surface area of
the fuel in the tank. This is why returning bypassed fuel
directly to the fuel pump intake or to a small unvented
header tank (where the separated air is allowed to
accumulate) may not be the best practice.
FWIW
Steve
Boese
Finn,
It seems to me that the problem you’re
seeing is consistent with the capacity of the pump not
being sufficient for the max flow required by the
engine and the pump flow capacity is decreasing with
use You appear to have checked everything but the
flow capacity of the pump under normal system pressure
which is what you really need to know. If you can
divert the returning fuel flow from the pressure
regulator to a measuring vessel and and collect that
fuel for an accurately measured time, the pump flow
rate can be calculated. This flow rate should be
greater than the maximum required by the engine by a
comfortable amount.
My apologies in advance if this is
obvious.
Steve Boese
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Hi Finn
Thanks for the reminder of my pump issue.
Yes, you chose more wisely the pump capacity.
Mine were way overkill.
So I’m thinking options are:
1. Fuel Pressure transducer fault - No - as
this was confirmed by the mixture monitor and
tune going out.
2. Power supply to pump via fault in
termination or switch current path - Unlikely,
given the slow reduction - I would imagine a
faulty connection would create a less uniform
symptom.
3. Alternator Battery voltage/current
reduction over time - No - You would see this in
the log.
4. Significant Fuel leak - No - Would think
this would have become obvious on inspection and
not intermittent.
5. Fuel Regulator - They are pretty simple
but unsure if they can fail with this symptom?
6. Fuel filter blockage - Certainly this
would have to be an obvious, but I take it you
swapped this out.
7. Pump internal failure -
Electrical
- ?
Mechanical
breakage - ?
Flow
Path - blockage - unlikely if filtered
effectively
Where is your pressure transducer in relation
to Reg/Any post pump filtering/Flow
Transducer/Rail?
If fuel regulator and filters can be
discounted, I’m struggling to trust the pump.
But your test had it sounding in good shape and
to spec.
So frustrating.
Cheers
Steve
Thanks Steve.
>From your March/April 2017 posts
it was a GSL392 that failed (high
current draw/low pressure, even after
you removed the insect you found in
the inlet).
So this afternoon I ran the pump for
about an hour. Amp draw from 3.04 to
286 depending on voltage. Pressure
between 43 and 40 psi (also depending
on voltage). No noticeable
degradation. Of course the difference
with this test is that no fuel went to
engine -- all recirculated through
pressure regulator and back to tank.
But no signs of a failing pump in
terms of higher current draw and less
pressure.
I guess I should put a temp probe on
the pump and see what it reads during
flight to see if that could be a
factor.
Finn
On 5/21/2022 9:01 PM, Stephen Izett
stephen.izett@gmail.com wrote:
Hi Finn
I had from memory a 393 fail.
Can’t recall the symptoms sorry.
I test before takeoff and then
run both pumps below 2ooo ft incase
of failure.
I plan to instal a comparator
relay board in fuel pressure circuit
to automatically bring on backup
pump and failure indicator.
So testing before flight becomes
- switch off and back on main engine
pump. This will save amps and wear
of backup pump.
When I switch off a pump at WOT
the engine dies pretty much
instantaneously and don't want to be
fiddling with a restart in the
Glasair which glides like a brick
with the gear out in the breeze.
Regards
Steve Izett
Recently I noticed my
fuel pressure being low.
Noticed because engine did
not come up in power when
advancing to full
throttle. Noticed mixture
real lean. Checking fuel
pressure as low as 28 psi
(normally 35 and up to 40
at full throttle).
Going over my engine logs
since first flight I now
see that fuel pressure has
been trending lower
through each flight --
more pronounced on longer
flights (40+ minutes).
More and more pronounced
over the months and became
really noticeable over
last month. Could explain
why mixture tuning appeared
to have changed. Nice to
have engine logs from
practically each flight.
But why? Pump getting
weaker?
My primary fuel pump is a
GSL414. I figured it was
wasted energy to push way
more fuel than needed
through the pressure
regulator back to the
tank.
My secondary (backup)
pump is a GSL393. When
turning that on, fuel
pressure comes back up to
where it needs to be.
Anyone have experience
with failing or weak EFI
pumps, particularly the
GSL414?
Finn
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