[Diy_efi] Sending unit confusion

Mark Bowers & Family mbalntel at cfw.com
Fri Feb 21 02:50:58 GMT 2003


Hi J,

OK, I Have read you post on the voltages you are reading on the 'yaller'
wire. The reason that it reads 12 v when disconneted is that you are
measuring back into the open circuit that is normally the output of the
guage or internal dash regulator.

The key fact that you have measured is the 0 to 55k range of the pot. In the
best version of your application, the voltage feed will come from the
circuit, not the dash. Question: Does this auxiliary half of the tank hook
to a fuel guage? Will you leave this connected?

While starting to draw this up today, I had a new qyestion: Do you really
want this transfer pump running all the time? It will reduce the pump's
reliability by a lot. An alternative is to have the transfer pump actuate in
a cyclic basis to pump so much fuel at a time. Whether this works or not
depends on your use. If you are racing, espcially off-road or some racing
where the fuel can easily slosh back to the auxiliary tank, it might better
to run the transfer pump all the time, like you seem to be planning.

Mark B.
----- Original Message -----
From: Toyota Supra <turbosupramk3 at hotmail.com>
To: <diy_efi at diy-efi.org>
Sent: Thursday, February 20, 2003 3:46 PM
Subject: Re: [Diy_efi] Sending unit confusion


> ok, just to be clear, this sounds like you want me to do this in place of
> the sending unit, is there a way to make the sending unit work outside of
> the car, but putting 12vDC into the yellow wire, and then putting
something
> on the other side of the second wire (brown with black)?
>
> the particular reason this appeals to me, is i can then move the float up
> and down, and watch it turn the circuit on, and turn it off, as well as
> visually see how much travel the float has to make, before overcoming the
> hysteresis.
>
> if not, i'll pick up a 55k pot today, the manual says that it should read
0
> to 55k when functioning properly
>
> thanks perry
>
> -j
>
>
>
>
>
>
> >From: Perry Harrington <pedward at apsoft.com>
>
> >Subject: Re: [Diy_efi] Sending unit confusion
>
> >
> >Measure the highest resistance of the sending unit, then substitute a pot
> >of
> >the same general value.  Just use 2 poles of the pot and leave the 3rd
pole
> >unconnected.
> >
> >--Perry
> >
> >On Thu, Feb 20, 2003 at 03:12:35PM -0500, Toyota Supra wrote:
> > > that makes sense, so it measures the current loss, it is sending 12vDC
> >out,
> > > but after grounding or whatever, only receives 0 to 3.5vDC ?
> > >
> > > so, how can i simulate what is in the car? can i measure resistance
> >between
> > > the brown w/ black wire, and ground, and then use that resitor between
> >my
> > > inverters ground and that particular wire? as well as running 12vDC
into
> >the
> > > yellow wire?
> > >
> > > thanks for the help perry
> > >
> > > -j
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > >Subject: Re: [Diy_efi] Sending unit confusion
> > >
> > > >
> > > >The sending unit may be connected like a temp sensor.  The sender has
> > > >a bias resistor between ground and the input.  12v is supplied to the
> > > >input of the sender and the output pulls the voltage up or down
through
> > > >the bias resistor.  If the sending unit isn't grounded, then with 2
> > > >wires it has to be biased externally.
> > > >
> > > >--Perry
> > > >
> > >
> > >
> > >
> > >
> > > > > >
> > > > > > > in my never ending quest to conquer this circuit, i have
> >encountered
> > > > > > > something very strange. when i removed the fuel level sending
> >unit
> > > >to
> > > > > >try
> > > > > > > and test my circuit, i found that i am not able to simulate
its
> > > > > >electrical
> > > > > > > function.
> > > > > > > the sending unit has 2 wires, a yellow and a brown w/ black
> >tracer.
> > > >when
> > > > > >the
> > > > > > > sending unit is not plugged into the body harness, the yellow
> >wire
> > > >has
> > > > > > > +12vDC (or whatever battery voltage may be) on the body
harness
> >side
> > > >of
> > > > > >the
> > > > > > > connector, and the brown w/ black tracer has approximately 15k
> >of
> > > > > >resistance
> > > > > > > to ground, or 35mV of positive voltage.
> > > > > > >
> > > > > > > when the connectors are plugged in, the yellow wire will have
> > > >anywhere
> > > > > >from
> > > > > > > 0 to 3.5vDC, dependent on the position of the "float". the
> >variable
> > > > > >resistor
> > > > > > > will have resistance ranging from 0k to 55k.
> > > > > > >
> > > > > > > now, my problem is, i can't simulate the variable voltage
> >outside of
> > > >the
> > > > > > > vehicle, to test my circuit. if i put 12vDC into the yellow
> >wire,
> > > >the
> > > > > >brown
> > > > > > > w/ black tracer will also have 12vDC, so what could that wire
> > > >possibly
> > > > > >be
> > > > > > > doing, or connected to, that would make the circuit and unit
> >work
> > > > > >properly?
> > > > > > >
> > > > > >
>
>
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