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Old 26-08-2020, 18:32   #1
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Diesel electric fuel pump question

Hi guys,


My question is: is the mechanical injection pump enough to keep fuel supplied to the engine without needing to run an electric pump continuously? It's a Bosch type mechanical pump and the bottom of the fuel tank is about inline with the bottom of the engine.


Background:


I installed my new engine and got it running but the electric fuel pump (the type that makes a distinct "tick tick tick tick" noise when on) stays running continuously. I thought this was an issue because on my old engine, it used to (or appeared to) only run if it was purging air from the system.



I contacted the marine engine manufacturer and they have advised that this continual running is normal behaviour. It quite probably is, but the old engine ran just fine without it running continuously.



There is a nifty circuit included in the design of the engine electrics that uses the field voltage of the alternator to prevent the starter motor from operating if the engine is running so it would be simple to rewire the pump to this circuit so it only activates pre-start.
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Old 26-08-2020, 19:10   #2
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Re: Diesel electric fuel pump question

We have a Universal M35B in our boat. It has an electric fuel pump that feeds a Bosh mechanical fuel pump. The electric pump runs continiously.
This engine has a safey system that shutsdown the electric fuel pump on low oil pressure. Energizing the pre-heat glow plugs bypasses the shutdown logic allowing startup.
Earlier this month the oil pressure switch failed causing the electric fuel pump to shutdown. The only sympton of this is no audible oil pressure alarm and the fuel pump not working.
Our boat ran normally until the tank dropped to approximately 50% and I was unable to start the engine.
This seems to be common in the Catalina 36 with this engine, as others have shared similar results.
Hope this helps,
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Old 27-08-2020, 00:08   #3
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Re: Diesel electric fuel pump question

If it's only lifting 30-40 cm ot should be fine without the electric running. I depends on how strong the spring is in the lift pump, my old 3GM30 could suck fuel up out of the keel tank the bottom of which was at least 1.2m below the lift pump. It's a suck it and see sort of thing.

Lift pumps generally have the cam shaft driving the suction stroke and the spring driving the discharge stroke, that way they don't over-pressure and burst the diaphragm.
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