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

[Alan Pemberton]

Hi Pat,

That's very interesting! I can't think what that wire is for - never would have made it as an Audi engineer:)

Alan

-----Original Message-----
From: p.carlier at telenet.be [mailto:p.carlier at telenet.be] 
Sent: September-11-16 11:23 PM
To: Alan Pemberton
Cc: urq at audifans.com
Subject: Re: [urq] Fuel gauge reads 3/4 when tank full

If you take the sender out of the tank , real pita job , you'll notice an uninsulated copper wire at the bottom of it . 
On the sender that is , not on the tank . 
Looks a bit like a braided ground wire . 
This wire is most likely broken or almost broken . 
Replace it or resolder it and the gauge should work again .

pat  







----- Oorspronkelijk bericht -----
Van: "Alan Pemberton" <alan_pemberton at telus.net>
Aan: urq at audifans.com
Verzonden: Maandag 12 september 2016 02:08:22
Onderwerp: [urq] Fuel gauge reads 3/4 when tank full

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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