Another Fuel Management Question

[Amylynn2202]

I am looking for an actual wiring diagram for my 2005 twin 300 hpdi round FMM gauge and sender harness.
I just finished a complete re rig on my center console. When I ran the motors in a dunk tank the gauge work like it should but after tying up the harness and splashing the boat I get no fuel flow readings, sync works fine, gauge check seems to work on first start but then I get no P. S. or gps reading. Just a dash, no o.o reading.
I am thinking possible a common wire to the flow sensors is broken in the harness some where or maybe bad gauge.

Any help would be appreciated

Thanks

[rodbolt17]

actually commen sense would work better than a diagram.
you have two flow sensors.
they are simple 5V square wave generators.
the orange wire supplies a 5V reference,the black wire is ground the third wire is the signal line going back to the gauge.
the signal wire can be monitored for Hz if your meter has an Hz function.

once the 5V ref and the ground path are in place there is a small coil and a paddle wheel in the flow sensor.
as fuel flows past that paddle wheel it spins.
as the paddles pass that hall effect coil it causes the signal line to switch between 0V and 5 V.
looks like a square wave signal.
based on how fast its switching the meter displays this in GPH.

works just about like a crank or cam sensor.

[boscoe99]

[Amylynn2202]

Boscoe, thank you very much for the diagram. That is exactly what I need.
Rodbolt, thank you also for the pin break down. Are you sure it is a 5v square wave or could it be a 12v square wave.
Common sense would be to gather as much information as possible before trying to diagnose a problem.

Thanks guys

[bajakeith]

5V reference

5V is a standerd in all EFI...do you have a sillyscope ?? LOL

[boscoe99]

Boscoe, thank you very much for the diagram. That is exactly what I need.
Rodbolt, thank you also for the pin break down. Are you sure it is a 5v square wave or could it be a 12v square wave.
Common sense would be to gather as much information as possible before trying to diagnose a problem.

Thanks guys

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