Fuel pressure switch question.

[nnyerges]

I am organizing and arranging all the wiring of my boat twin inboard diesel engines instrument panel and I have little doubt about the switched +12VDC power of the instruments.

They are currently connected as shown in the diagram INS1.PNG. Obviously, the ?fuel pressure switch? is only to feed the instruments main +12Vdc. The questions are:

1. Is that ?fuel pressure switch? is only installed, to feed the instruments?
2. Is not enough to power the instruments form the +12Vdc of the ING.SW (See diagram INS2.PNG)?
3. Maybe I have mistaken identified the complete route of the ?fuel pressure switch?, but its goes somewhere else into the engine?

Thanks in advance

Note: The diagrams show the starboard side only. The port side is identical.

 

[Silvertip]

Re: Fuel pressure switch question.

Perhaps there are electric "lift pumps" in the system. If that's the case, then having the instruments powered by a fuel pressure switch would make sense as it provides the captain with a visual indication that the pumps are working. If the instruments go dead or fail to energize that would be an indication the lift pumps are not operating. If there are no electric pumps then I have no idea why they would be wired this way and your proposed wiring in diagram #2 would work fine. In a purely mechanical injection system, having the instruments powered through a fuel pressure switch would serve as an indication that fuel pressure is lost but that would be immediately obvious since the engine would quit at the loss of fuel pressure. So -- the answer is I'm not a marine diesel guy so "I don't know". But I'm sure Don S. does and he should be along shortly.

 

[nnyerges]

Re: Fuel pressure switch question.

If there are no electric pumps then I have no idea why they would be wired this way and your proposed wiring in diagram #2 would work fine. In a purely mechanical injection system, having the instruments powered through a fuel pressure switch would serve as an indication that fuel pressure is lost but that would be immediately obvious since the engine would quit at the loss of fuel pressure.

There is no electrical fuel pump, so diagram #2 will work, but im trying to figure out why manufacturer put that sender to feed the instruments and here is my conclution:

Feeding the instruments true the "fuel pressure switch" sender, guarantees you that batteries don’t drain in case you forget to turn off the ING.KEY at motor stopped (in diagram #2). If no fuel, like tank empty or mechanical fuel pump damage, or any other mechanical reason, engine will stop, the engine oil low pressure alarm, alternator idiot light and gear/drive oil pressure alarm will do the job and there is no reason in having the instruments on (like feeding directly from the ING.SW).

 

[Don S]

Re: Fuel pressure switch question.

I'm no help on this one, haven't been around a Detroit close to 20 years.

 

[nnyerges]

Re: Fuel pressure switch question.

Here is a picture of the Fuel pressure switch..