[urq] Fuel gauge reads 3/4 when tank full

[Alan Pemberton]

This problem was noticed when I had the car filled up and only reached 3/4
of a tank.  I couldn't be certain that the tank had been completely filled
so, yesterday, had it filled up completely but the gauge does not go above
3/4 tank.

 

I thought at first that I had a problem that hadn't come up on the list but
not the case!  10 years ago Louis-Alain had the same problem and provided
the relationship between sender resistance and fuel level (see below).  My
tank, completely full, reads 63 Ohms so the issue must be the sender.

 

There are some comments in the email thread started by Louis-Alain noting
that the orientation of the sender in the tank must be correct.  The sender,
as far as I know, was never removed before I purchased the car in 1993 and
has not been touched since.

 

In the Audi system, the sender appears to be part of the fuel tank and not
available separately.  Does anyone know the cause of this issue and if it is
fixable?  

 

Alan

1985 urq

 

-----Original Message-----

From: urq-bounces at audifans.com [mailto:urq-bounces at audifans.com] On Behalf
Of Louis-Alain Richard

Sent: October-11-06 12:44 PM

To: urq at audifans.com

Subject: [urq] Mine will not read full : anyone have a fuel guage?

 

Addendum to my own post:

 

The resistance values of the VAG1301 are not true ohms values, as per this
page (look at the bottom for a chart)
www.bentleypublishers.com/tech/vw/bentley.vw1301.testing.htm?ticket=none

 

I've plotted the data from this page to obtain a graph of the relationship
between VAG1301 and real values.

 

Hence, to test the fuel gauge circuit, you must use these real ohms values

:

 

                                Real value                           VAG1301
values

Full tank               39 ohms                               60

Half tank              88 ohms                               155

Reserve               159 ohms                             302

 

It all makes sense, because I've already tried the VAG1301 values and my
fuel gauge wasn't even near the corresponding marks. So all you need is a

40 ohms resistance and place it between the 2 wires at the sending unit and
your gauge should read FULL. If yes, replace the sending unit, if not check
elsewhere. Mine works beautifully. 

 

Louis-Alain

 

 

> 

> > -----Message d'origine-----

> 

> > And if you don't have a Bentley, you can look at these scans of the 

> > official WR shop manual...

> >

> > http://www.wrquattro.com/info_data.html

> >

> > Fuel gauge testing is at page 127

> > (http://www.wrquattro.com/QuattroManual/QuattroManual131.jpg)

> > and IC voltage regulator at page 126 

> > (http://www.wrquattro.com/QuattroManual/QuattroManual130.jpg).

> >

> > Louis-Alain

 

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