Erratic Fuel Gauge

I have a 1998 A6 2.8 Quattro Avant ( uk car) with 150,000 miles in very good condition & full history. Lately the fuel gauge has been playing up, showing
full for 150+ miles then dropping rapidly until it gets to half, if I then fill it up I can get 50-55 litres in (70 litre tank) so obviously something is wrong. I have removed the tank cover and operated the float by hand and the gauge does not go below half even when on the bottom of its travel, anyone got any suggestions as to whether its the tank unit or the gauge, or possibly a voltage regulator somewhere, (everything else works fine). If its the tank unit should I try a second-hand one as I imagine that to by a new Audi part means taking out another mortgage to pay for it.
Any help would be appreciated
Graham
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"Graham Humphreys" wrote

This is actually quite common on many Audis. Most of the time, the fuel sending unit needs replacing. See if this link can help you:
http://www.robsaudiworld.com/fuelrepair.htm
Second possibility is faulty gauge, but I'd start with the FSU first.
Good luck,
Pete
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"Pete" wrote

I also forgot to mention that in the US, somewhere around year 2000, there was a whole Audi customer service action that included free replacement of fuel sending units with the updated ones (apparently the older ones on '96-'99 model years were prone to premature failures). This was specifically for the A6. So, you may want to call Audi Customer Relations in the UK and see if they had something similar going and if so, they should fix it for free, even if you're no longer under warranty.
Cheers,
Pete
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Ive got the same model tho its a 99 year. 112k miles and had it since new.
The fault is exactly the same.
Audi 1st replaced the sender at 35k miles for free. It failed again at 80k and they wanted 150 to put a new sender in. Ive just lived with it and always use the trip meter to calculate tank.
The 2.8 will do 328 miles on a full talk before it splutters to a halt! (and I know that for sure as it happened to me)
Now I always carry a spare gallon in the back and always fill up when I get to 300 on the trip meter.
Ive seen the post already shown about the repair, Im just wary of opening up the fuel tank due to the obvious fire risk. Plus if you dont have the right tools and dont seal it properly afterwards you will have a petrol smell inthe car for ever, as the hatch is below the rear seat cusion.
Cheers, John.
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I would be more worried about fire risk by carrying the gallon in your trunk than opening the tank access.
If it is anything like the tank in my '91 100q (which I think it is) access is quite easy and wouldn't require any special tools. Just wait until your tank is nearly empty to do the job.
Plus if you dont have the right

The access has a seal and should not be a problem.

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