Audi A8 4.2 Quattro Sport Fuel Pump problem

[garethn]

Hi
I have a 2001 Audi A8 4.2 Quattro Sport.

Problem is that the car sometimes won't start. Fluffs, fires on couple of cylinders, then dies, leave it for a while come back then it goes and runs perfectly.

Originally thought it was out of fuel with a faulty guage, put fuel in, started. Then fault re-occurs later with a full tank of fuel, only this time, no fluffing and missing, just no signs of it firing up at all.

I investigate by opening the hatch at the top of the tank, located just behind the offside rear seat located in the boot. Pulled the electrical plug off, opened a lid at the top of the fuel pump (I guess) which contained a big spring, put it back on. Tapped it a few times.

Hey presto, car starts and has been running for a few days since with no problems.

The in tank fuel pump costs over £600 plus vat from Audi. The local dealer says they have never sold one and so I should make sure it is the pump before buying it.

I would be interested to know if anyone else has had a similar fault or maybe somebody technical could suggest some other possiblities, like an electrical relay, faulty float etc that may stop the pump functioning occasionally.

Also, if it does need a fuel pump, does anyone know where I can find one that doesn't cost so much.

Cheers

Gareth

[a8 tech]

yes the pumps do fail and there a pain in the **** to fit and very exspensive.There is one other solution to this issue and it is are old friend water ingress in the plenith chamber.The engine control unit is located on the pssenger side of the plenith chamber in the plastic e box and it is very prone to water entering the box and bob monking the control unit and the electrical contacts.The drain vents in the plenith chamber block up with crap and the rain water backs up and the problems begin.Get some fault codes and if there are loads in engine management goto the e box and have a look

[garethn]

Thank you very much for your information, I have a diagnostic code reader coming in a couple of days, another thing you might be able to help with is where to find the plug on the car to read the codes.
Workshop service CD and missing driver manual are also on their way soon. If you can point me in the direction of the plug hole in the meantime, would be much appreciated.
Cheers

[a8 tech]

Attachment 994Front centre consule (ashtray)

[garethn]

Hi
In Tank Fuel pump all changed and sorted now, thanks for the help. It was knackered after all.

I have an intermittently flickering abs light along with skidding potential warning light (same as when you press the ESP off button) coming on now, shortly followed by a low brake pads warning light, maybe they are all linked to worn pads though.

All the reviews said deep pockets were needed for these cars and they weren't wrong.

[a8 tech]

There a great car and not so exspensive to run if you are having a go yourself with a little help from the forum http://www.audipages.com/Tech_Articles.html

[Phil Thompson]

My A8 has had several new fuel pumps. The problem as I understand it is that the pump is not immersed in the petrol like most cars but sits higher in the tank and relies on a seal around the pump to hold fuel to prime the pump. If this seal leaks and allows the fuel to drain away then the pump runs dry and rapidly fails (it uses the fuel as a lubricant). If the pump has lost its prime a litre of fuel poured into the tank will reprime it and get you going again, but this is only fixing the symptom and not the fault. Similarly, replacing a failed pump without changing the seal is only a temporary solution, it will soon follow its predecessor.

[a8 tech]

i disagree and it sounds like you had a bad experiance,but yes the seal must be replaced when ever it is removed.Having fitted fuel pumps for customers over 3 years ago and still servicing there cars,they have never had any other fuel pumps so again i must say your circumstances arent clear and its the first time ive have heard of this repeat failure since a8 launch

[jaano]

I have the same problem - there is not enough fuel to keep engine running - 1st it starts after prime (fueling) with a little troubles, it doesn't wont to go at higher rotates and next it stops.. I've destroyed 2 pumps and waiting for another one... maybe the suck hoses are closed/cloged..?? I've no idea.... maybe the seal is leaking (I have not chenge it..)
do You have some ideas?

p.s. I broked nipple of the picture http://forums.audiworld.com/a8/msgs/110843.phtml
marked in red/pink - maybe this is the reason - i prelonged it by pipe/hose but I don't know if it jumps...

(sorry for my language - I've not used it for a lot of times...

[garethn]

I purchased a new pump from audi and fitted it with some experienced help. Everything has been fine since.

I bought the pump from audi at a cost of around £600, the entire kit came, big white plastic thing, pumps in the bottom, new seals, new top etc.

We followed the audi maintenance instructions that I purchased from ebay on dvd, which are worth their weight in gold by the way, and everything has operated fine since.

I only have a couple of lambda sensors, an atf oil change due to a faintly whiny box noise developing and a couple of suspension knocks to fix, along with a couple of tyres and the massive amount of fuel it takes its planning on keeping me skint for some time to come.

I loves it though :-)