I agree with you regarding purging air, warming up not so much.
If your purging air theory is correct, there must be a small air/vacumn leak
somewhere in your system between the tank and injectors that lets air in the
system while the boat in sitting in the water between your uses of it.
When finally running, and the accumulated air has been passed thru the engine
back to the tank, etc. the leak is so small as to not be a problem.
As it sits and the system accumulates air, it has too much air/not enough fuel
to run until the accumulated air has been ‘purged’ as you suggest.
As a test of this, you might bleed the system before you start the engine. If
you see air bubbles then, it’s likely that is the problem.
If no bubbles, back to the drawing board.!
Charlie Nelson
Sent from the all new AOL app for iOS
On Friday, June 30, 2023, 1:18 PM, David Knecht via CnC-List
<cnc-list@cnc-list.com> wrote:
As I have thought about this and tried to come up with a cause, another data
point occurred to me about the sequence of events. The stall has happened on
3 occasions on three different days in the last few weeks and not on 5-6 other
occasions under similar conditions. In each of the cases where the engine
stalled, it always happened within the first minute after starting the engine.
In each case, the engine started and then stalled several times ( run for about
10 seconds then stall, repeat 2-3 times) and then after waiting a few minutes,
it started and ran fine for extended periods. Those symptoms seem like limited
fuel getting to the engine causing the stall, but I don’t see how they can be
fuel filter related. But I realize that I always left the key switch on and
thus the fuel pump running between start attempts. Any way they could be fuel
pump related in the sense of it running for a while (warming up or purging air)
while waiting to restart? Dave
S/V Aries1990 C&C 34+New London, CT
On Jun 28, 2023, at 8:53 PM, Neil Gallagher via CnC-List
<cnc-list@cnc-list.com> wrote:
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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Thanks for your help.
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me pay the associated bills. Make a contribution at:
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Thanks for your help.
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