[alfa] 164 fuel gauge followup

[AlfaRs@xxxxxxx]

I posted a question a few weeks ago about the problems that
I have had with my 164's fuel gauge. A summary of this is
that the gauge never read below < tank.  I only got a few
responses witch generally stated use the odometer to judge
fuel remaining.  Well for a few reasons I can't accept this.
One, my wife and 1-1/2 year old generally use this car so
getting her to re-set the trip meter is basically impossible.
Two I just can't accept a system this simple not working the
way it should.  Three just after buying this car a few years
ago I ran it out of gas on a road trip to PA with the family. I
can't take another "I told you so" from the wife!

I replaced the fuel level sending unit thinking that it was
the most likely problem.  Well I should have done some
test first because it really didn't make any difference.

So a week ago I headed out to the car with a multi meter and
a 2k potentiometer.  I simply measured the resistance of the
sending unit at various levels and found it to be good.  So I
plumbed in the pot and checked my gauge readings at various
readings.  The correct values are listed in the manual.  This
is what I found.

    Measured    Spec
Full    2-8 ohms    0-6 ohms
7/8 50
>   86             59-69
5/8 111
=   140            116-126
3/8 189
<   221            186-201
1/8 276
Empty   263-409  295-315

So basically I determined that my gauge is out of calibration.
I don't think that a dirty connection would require more
resistance to make the gauge read correctly.  I would assume
that the opposite would be true.

The wire harness has three wires going to the sending unit.
A black, purple, and purple/black.  The black is ground
purple is gauge reading and purple/black is the low warning
light.  What I did was to insert 30 ohms of resistance
inline on the purple wire.  I used bullet connections so it could
be quickly undone or resistance changed.

I happened to have a few 10 ohm 10 watt resisters lying around
so I used 3 in series.

The end product is that my gauge is at about 1/8 when the light
comes on (should be 2.2-2.4 gal remaining) and reads just a hair
below the full mark when topped off.  If my calculations (and
guesses) are correct it should read Empty when it is.  I will have
to test this out one day but I have  17 gallons of fresh gas in the
tank so it may take a few weeks.

YMMV (and probably will)

Dave McCrory
Maryville, TN
93' 164
87' Verde
87' Platinum
87' Gold
76' Spider
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