David,
This may be a long shot, but on a Universal M3-20B that I installed on a
club launch, and I think all Universals, the fuel pump gets its power
under normal running conditions via an oil pressure switch. When
starting the engine, the glow plug switch energizes the electric fuel
pump in addition to the glow plugs (you can hear it clicking when you
press the glow plug switch), but once the oil pressure rises it closes
the oil pressure switch and keeps the fuel pump running when you let up
on the glow plug switch. Incidentally the reason you hear the pump
running after you shut the engine off is that it takes a few seconds for
the oil pressure to drop to the point where the switch opens.
I ran in to a problem with that engine when sludge got in to the
connection to the oil pressure switch and kept it from closing properly,
and thus the fuel pump intermittently stopped running and stalled the
engine. Until I found the real problem I put a relay powered by the
engine on/off key switch that powered the fuel pump directly, but when I
flushed the oil switch a few times it cured the problem.
Not sure how relevant this may be to your issues, but may be of interest.
Neil Gallagher
Weatherly, 35-1
Glen Cove, NY
On 6/27/2023 12:45 PM, David Knecht via CnC-List wrote:
So I am back to my engine problem hoping someone can help clarify
things. I have had the engine quit several more times, but with no
consistency as to when or why it happens. We were on a cruise recently
and used it often and for long periods going in and out of harbors.
Mostly it worked fine but had it stall several times: start and run
for a few minutes, then stall, restart then stall, restart then stall,
then run fine for 20 min or more. This happened in two separate
situations a few days apart but no stall several other times. In all
cases, it has eventually restarted and ran for extended periods.
These intermittent problems are the hardest to diagnose in my
experience. This seems most likely to be a fuel related issue so now
I am trying to fully understand the fuel system.
I installed a Racor 500 unit last summer with a T-handle vacuum gauge
on top. Fuel goes from the tank, through the shutoff lever to the
Racor, then to the fuel pump, then to the secondary and on to the
engine. If I understand this correctly, the gauge on the Racor unit
will measure restriction in the fuel flow upstream of the gauge, ie
the primary (30 µm in my case). I know the gauge works because if
you partially shut off the fuel lever, you see the gauge gradually
increase in vacuum reading. But it seems that it will not tell you if
the secondary is plugged.
1. I don’t see how the secondary (10 µm in my case) could be plugged
if the primary is fine but I guess not impossible. My temptation is
to replace the secondary since the primary is not showing any sign of
being plugged (from the gauge), but I don’t see how this could lead to
an infrequent intermittent stall.
2. Fuel pump problem (loose wire etc.)? You can hear the fuel pump
running when the engine is off and I have never heard it stop or
pause. Can fuel pumps fail like this? Can that lead to an
intermittent stall?
3. Air getting into fuel line- seems possible, but I don’t see how
that can be the cause if the engine runs for an hour continuously once
restarted.
Any ideas welcome! Dave
S/V Aries
1990 C&C 34+
New London, CT
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