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AQ130C - Changed Gearbox Ratio - Problem?

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sandkicker said:


My 2006 MERC 5.7L MIE with TKS carb (2bbl) has an electric fuel pump with an "no oil pressure" switch. Works fine. The electric fuel pump's output pressure is set so that won't overcome a carb float's cut off.
I'll bet you that the 2006 Merc ECU/ECM does the same as the N/O LOP Switch does for these other systems.


Re" fresh air in engine compartment"... The bilge blower system is not intended to furnish cooling air or combustion air to the engine compartment. It is only intended to scavenge any possible gas fumes from the bottom of the bilge.
I would hope that both aspects of this are satisfied via a blower motor system.
Click to expand...
 
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Hi, You've said the ​
electric fuel pump's output pressure is set so that won't overcome a carb float's cut off ​
- which is great - and what I was thinking (hoping) would be the case. Having spoken today with someone at the company that supplied my guys with the carb & their recommended fuel pump he's told me the same plus the pump is also designed to limit itself somehow when not having to deliver fuel.

So the oil pressure switch cut-off is primarily aimed at concerns about a potential failure mode e.g. not in normal use (as described):
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Worst case scenario:
fuel line becomes severed or disconnected.
engine eventually stops.
pump continues to operate while fuel is being pumped into the engine bay.
gasoline ignites, catches the boat on fire, you and/or your family and friends become severely injured, law suits occur, your Marine Insurance Policy does not cover the incident due to "negligence", etc. etc. etc.
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With a very simple to install N/O Low Oil Pressure switch and relay, this is avoided. ​
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Understood - is it possible to buy an oil pressure switch that has two sets of contacts (1x NO + 1x NC)? I've just drawn up the attached schematic which I hope does what's been described but I'm thinking I need the existing oil switch contacts (that must be NC e.g. closed without oil pressure - for my warning light) and another set NO that will close when there is oil pressure to make my fuel pump run. Look OK?171018.jpg​

As you'll see I've already asked the guys to run the pump via NO relay contacts - because I didn't want the pump's additional current to pass through my existing ignition switch (and to give the pump it's own dedicated in-line fuse and have a good supply voltage due to suffering almost no volt-drop on its supply cables). Could the momentary (NO) push-button be located not at the helm itself? To have it there would be convenient but I'm struggling to think where I can put it. And, if it's only ever pushed for a few seconds to ensure the float bowl's full I'm wondering if it go elsewhere (kinda hidden away)?

Thanks, bye.



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RicardoMarine said:
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Click to expand...

likely to get away with it with an AQ130 engine. But with larger engines??? Remember blower provides a low pressure (scavenge) point at the lowest part of the bilge...i.e. remove air from bilge that is replaced (theoretically) by air from the front vents... The air inlet to the engine requires a (cool) inflow and is at the highest point of the bilge. Would think that a nearby vent to the atmosphere would be the best source of air for the engine... not a flow that is more than half the length of the boat.
 
The N/O LOP Switch will be two pole. (not same as what you show in your drawing) In other words, it will close a Positive current circuit, activating the pump's relay once closed.


And yes... if a "Start-bi-Pass" system is not used, the Momentary switch would be at the helm.
One push or toggle of the switch, and the fuel pump relay would be triggered for as long as you held the switch closed.


I think that you are overly concerned about the fuel pump when the carburetor float bowl is full.
As the bowl reaches MAX capacity, the float will close the needle/seat, and will temporarily slow or stop the fuel supply to the bowl.
The pump won't care!



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Hi, bit confused - you've said "The N/O LOP Switch will be two pole. (not same as what you show in your drawing) In other words, it will close a Positive current circuit, activating the pump's relay once closed." Confused - because that is what I've shown. One pole is N/C (no oil pressure = closed to earth down the oil pressure warning light) the other is N/O (only closed when there is oil pressure to earth down the pump for it to run). I could use this contact to earth down my control relay instead if tbe LOP switch contacts can't handle 5A but would prefer to earth down the pump itself so that the LOP is acting directly on the fuel pump itself. But do they make the N/C + N/O switch? Do you have a diagram of one you' e done?


And yes... if a "Start-bi-Pass" system is not used, the Momentary switch would be at the helm. I was wondering if USCG secify that it has to be at the helm or could it be positioned elsewhere and still comply?

Thanks, bye.
 
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