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Re: Fuel Gauge Adjustment

kirby.a.smith@lmco.com wrote:
> ... said wire breaking and revealing its presence by the loss of 
> the right half of the panel illumination) ... 

Something else to check when only one half of your instrument panel
illuminates is the coper contacts on the printed circuit "film" for the
bulbs.  For a couple of months I drove around at night being unable to
see the tachometer on my car.  Then one day I decided to finally fix
it.  I took my trusty old multimeter and sure enough, there was power
going to the bulb.  So without thinking any more about it I went and
replaced both bulbs with new ones (thinking that if one failed, the
other one can't be too far off).

Next time I'm drivng at night I feel so good about my acomplishment when
both dials light up.  Then, after a few munites, the other side goes
dark.  After a few days, the whole cluster was dark - so much for
feeling good about my acomplishments.  It turns out that even though the
contacts for the bulbs looked fine, they had a thin layer of oxidation
that I could only get rid off using fine sandpaper.  I believe this
contact resistance is also the culprit of the overheated and melted
plastic around these bulbs.  It was actually harder to remove than I
thought at first, but after doing it, the whole instrument cluster
lights up bright and steady :-)

> For the trip computer, a very narrow but long screwdriver is needed.  
> I made a special tool from a heavy gauge coat hanger wire, cutting out 
> an 8-inch section, and grinding one end to resemble a flat blade 
> screwdriver.  This blade is inserted into the hole through the center 
> of the shaft described above and used to turn a mini-potentiometer 
> that is mounted at the back of the instrument panel.  (One could get 
> to this from below, probably.)  With a full (!) tank, turning the 
> ignition on while holding the trip computer reset button down and 
> having the function pointer on miles (or km),should yield the display 
> of a number specified in the Bentley by model.  (650 for 90 quattros)  
> The potentiometer is adjusted to make the display show the specified 
> value.

People should know that this gauge is actually adjusted using a small
allen key (~2.5mm).  It only has about 9/10 of a turn of adjustment and
only adjusts the range function, not the mpg function.  Start by
adjusting the mpg's and only then worry about the range adjustment.  The
number that shows up during the adjustment is supposed to be the liters
of fuel remaining multiplied by 10 - so make sure the tank is full
before doing any adjustments.


Luis Marques
'87 4kcsq