Hi Paul,

Sorry I'm late to this discussion!

You can test the pump relatively easily.

Bentley describes a procedure to test it:
It says that fuel volume is measured at the fuel return hose under the bonnet...remove fuel pump fuse (#1 on row #4), ignition off, jump 12v to the lower socket of the empty fuse receptacle. You should get minimum of 350ml of fuel in 15 secs...anything above that, volume is good.

Ok - first of all, the fuel return hose - there are 3 separate hoses at a junction near the right hand (drivers side) shock tower (you'll need to remove the solid plastic inlet pipe to view them).
The hose you want is the tank return hose after the down stream side of the fuel pressure regulator. This hose is not under pressure and is safe to separate. Using this hose means you measure volume that the pump pushes under rail pressure (4 bar ~ 60psi) through the fuel pressure regulator. The area where the three hoses are all together should have a series of joiners for each hose with crimp joiners holding them in place. I cut through one of these crimps, separated the hose and used a 1 foot length of whatever hose I found in the garage (vacuum probably) and fed from the fuel rail side into a margarine container (600ml coke bottle or similar will do too, it won't be in it for long).

Next, you can do as Bentley suggests and hotwire the fuel pump fuse.
Alternatively, you can do what I did and hotwire the pump directly from the battery with a toggle switch, as it's all in the boot - remove boot carpet, open the pump inspection hatch, unplug pump/fuel sender plug. The pump power is the heavier gauge wires.
Power directly to pump, earth via a toggle switch - it's all spade connectors, so easy peasy with a crimp set!

With everything in place (you'll be in the boot, so wedge the margarine pot/coke bottle somewhere), flick the toggle switch and count 1001-1015!
If it works and is able to push 350ml or more past the fuel pressure regulator, the pump is fine.

My 2c on fuel pump replacement:

1. Never do the long bolt up too tight - this is critical. Overtightening of the long bolt will deform the plastic surrounding the captive nut at the bottom. The nut will come loose in the plastic, and good luck ever getting that bolt undone again!

It's easy to judge by feel, you can feel it compressing the rubber on the metal/rubber "arched window" gasket, then when it contacts the metal it goes hard. Stop tightening right there - DO NOT TORQUE IT DOWN!

2. Metal rubber gasket.
On my car, I replaced this and the o-ring. But the price on this little kit has gone up significantly since I did mine.
My philosophy is to always renew seals on items like this, but I have to say that the gasket on my car was in very good condition, and could probably have been reused.
One suggestion I have seen was to use a rubber rejuvenating product (one with plasticisers such as ATP AT205) to soak the seal in overnight to soften and rejuvenate the seal.

3. Removing and reinstalling the pump assembly:
I've watched videos and read people's accounts of removing and reinstalling this pump.
It has a narrow area in the tank, which the assembly has to pass through as it goes in and out of the tank. People push, and pull, and twist, and rip this assembly out of the tank.
This is completely unnecessary.
The pump is shaped like a step, and to remove it you simply pull upwards, and then twist it around gently while pulling and remove it like a corkscrew. I think its anti-clockwise out, clockwise in, and about 180° of motion, but don't quote me!
It will come out easily, and if it doesnt, you're doing it wrong.
Just note it's orientation when removing so you know where to reinsert it. Once seated back in the tank, there are two triangles to line up (one on the tank hole and one on the pump assemnly top) and it should go there easily without force.

4. Inner tank pump housing recepticle:
This is the large housing inside the tank with all the suction hoses coming off it.
It has a hook, which hangs off the tank filler tube at the top centre of the tank. It's a bit like a plastic coat hanger, but very heavy duty.
Pump removal can knock this hook off the filler tube. If it does, you'll never get the pump assembly seated properly.
It's pretty easy to feel inside the tank for the hook and make sure it's over the filler tube (the filler tube runs roughly horizontal across the top of the tank, and feeds directly into the fuel pump bowl once it's installed).

***Car is back on the road!***
 

Thanks to all of the wonderful posters here, I am delighted to say that my car is back on the road after I replaced the fuel pump. I don't recommend doing this yourself if you are rich enough to pay someone else to do it. :ROFL:

I sourced the VDO fuel pump form the USA for 145USD plus shipping to Australia. The cheapest that I could buy it locally for was 540AUD :tuttut:

I really appreciate all of the tips, help and advice that I received here in this community. It made my job a lot easier. This job was very fiddly and complicated. The 22 year old plastic housing scared me. At over one thousand dollars new, I knew that I had to be careful and probably lucky too.

I have assembled a document detailing my 'adventure' and am posting it here. It may be good for a laugh!

Attachment 23045

Thanks again!

Yay! :)

Triple yay from me. The documentation was an interesting read. I'm so pleased you got it sorted.

Nicely done! ++++++

I wouldn't have thought it necessary to "celebrate with several whiskeys" after sitting in the boot for hours getting high on petrol fumes. :D

After driving my S8 and guzzling 72.8 litres of fuel from the tank, I am happy to report that the car started more or less instantly each time, and was down to the reserve with the petrol bowser tell tale indicator showing in the cluster display when I finally filled up.

This indicates to me that I must have installed the fuel pump housing properly and that it is safe for me to assume that this particular repair measure is complete. The Audi documentation says that I should perform a certain fuel leak test on an empty tank, but I think that I can forgo this and just drive the car with confidence. Yes?


I'll second that! I am so relieved.

Glad you found the pdf interesting. The repair was an adventure for me and an exercise in patience! I am also very pleased to have fixed the problem with so little diagnostics.

Thank you, thank you! My sense of smell has suffered since the back seat of my C4 A6 Avant caught on fire during a road trip a couple of years ago. I had to drag the seat out of the car and put the fire out with a bottle of orange juice.

I think that lack of smell affected me psychologically when I did this job, because I could not really smell the petrol and so, did not get high on the fumes. (Kind of like the logic of the Ravenous Bugblatter Beast of Traal if you have read Douglas Adams) Consequently, I felt that I did need to celebrate with some whiskey!
Attachment 23071

I shall be sure to keep a towel on my head next time I do the job :ROFL:

:ROFL:

If you think of my username as initials you might notice it stands for something (something that equals 42). I've always been a big fan of Douglas Adams' work. +++

Well, well, well!

Meaning Of Life, The Universe And Everything. :ROFL: *=42 ASCII AKA anything/everything. I don't think that I realised that until tonight. Thanks for leading me to that. ++++++