Peter is on the money here, as usual. I would add that the resistance
should drop to around 10 Ohms when the float arm is in the tank full
position.
If you look carefully at what moves as the float arm swings, you'll see a
tiny brass contact which slides along the wires of the rheostat, this moving
contact point brings more and more wire length into the circuit as the float
arm drops, thus raising the resistance to the 70-80 Ohm range. These values
are NOT critical - if you have this sort of resistance variation, anywhere
in the ballpark of these number (say within 30%), the fuel gauge should work
pretty well..
If the sender is doing all this, your problem is probably elsewhere. Try
grounding the wire at the sender terminal (momentarily, don't leave it
grounded as this is a little hard on the dash indicator). Now see where the
indicator goes - it should go to full tank and even beyond. If it does,
there is nothing wrong with the dash unit or the wiring, and your problem
may be a poorly grounded tank (if there is no grounding wire, add one), or
it is possible your float is not floating, thus the tank always reads empty.
If this is your problem, drain the gas out of it and resolder it. You can
expel the gas from it by heating it in hot water, with the hole above water
so you can see the gas come out.
Dick Benjamin
----- Original Message -----
From: "Peter Engel" <peter.engel@xxxxxxxxxxx>
To: <mailing-list@xxxxxxxxxxxxxxxx>
Sent: Monday, May 19, 2003 1:51 PM
Subject: Re: IML: fuel sender
> Bruce,
>
> There should be 0 ohms resistance between the stud outside the sending
> unit and the "close" end of the resistance wire. There should be about
> 80 ohms (I think) resistance between the stud and the "far" end of the
> resistance wire WHEN THE FLOAT IS IN THE TANK EMPTY POSITION.
>
> The circuit is simply a loop from the stud, through the resistor, to
> ground (the fuel outlet pipe). The float position determines how much
> of the resistance wire is bypassed when current flows through the float
> arm wiper.
>
> Hope this makes sense.
> Pete in PA
> 70 LeBaron
>
> Date: Mon, 19 May 2003 10:25:10 -0700 (PDT)
> From: Bruce Stubblefield <audiblefeast@xxxxxxxxx>
> Subject: IML: 69 FUEL TANK SENDING UNIT
> In lieu of paying $140 to have my fuel tank
> sending unit rebuilt, I thought I would take a whack
> at it.
> Inside is a simple rheostat wound around a flat
> piece of insulator. This little structure appears to
> be insultated from the metal chassis of the sending
> unit. When disassembled, there is full continuity
> between the wires of the rheostat winding and the
> contact screw which attaches at the outside of the
> senidng unit to the gas guage lead. Is this right? I
> thought that a varying resistance in this circuit what
> what the gas guage was measuring?
> Any helpful hints?
>
>
>
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