Fuel delivery issue
 

hi. i have had a 99 A8 quatro for three years now. most recent problem has had it laid up for a month now.

i have read about the fuel pump issue and think i have the same thing. fuel in one side of tank does not get to other side according to the mechanic. the pump has been replaced as well as the relay.

now they want to replace the entire tank ($1100 part and 18 hours of labor).

any thoughts before i start digging a grave for it in the backyard?

thanks

The new fuel pump should have fixed the problem, assuming.....
 

the mecahnic installed it correctly. The only possible non-pump issue that could cause this is a clogged or broken tube from the far section of the tank to the pump, which is very unlikely. Your mechanic should be able to look into the tank and investigate this. It seems like the mechanic is trying to take the easy/expensive (for you) way out rather than doing a little work, IMO.

The fuel pump is tricky to install according to the Bentley
 

The procedure has a lot of twists and turns, literally. I would not be suprised if it is installed incorrectly. They list this as a symptom.

Re: Fuel delivery issue
 

Maybe this helps to understand the way it works.


<img src="http://pictureposter.audiworld.com/79649/a8fueltank.jpg">

1 23 Nm
2 Cross brace
- Flexible packing pieces must be fitted between cross brace and securing straps.
3 Fuel supply pipe
- To injection system
4 Banjo bolt - 23 Nm
5 Seal
- Renew
6 Fuel return pipe
- From injection system
7 Fuel supply pipe
- To auxiliary heater



8 Double hose clip
9 Connecting hose, lower
10 Fuel tank
11 Cross member
- For tank
12 23 Nm
13 Securing strap
- Note differing length
14 Securing strap
- Note differing length


<b>Function of fuel system</b>

<img src="http://pictureposter.audiworld.com/79649/a8fueltank2.jpg">

The fuel tank employs a multi-chamber system.

The dual-stage electric fuel pump is located in a baffle housing (not shown in illustration).

The first stage of the fuel pump produces a stream of fuel (large arrow in illustration) which is directed to the three suction jet pumps -2-, -3- and -5-, where it is passed through a nozzle and thus accelerated. The accelerated jet of fuel draws off the surrounding fuel in the individual chambers (fluid entrainment principle) and delivers it to the adapter plate -1- in the baffle housing via a system of pipes.



The second stage of the electric fuel pump delivers the fuel from the baffle housing to the engine.

The first stage of the electric fuel pump, the system of suction jet pumps and the baffle housing together form a closed circuit inside the fuel tank.

For reliable starting, there must be fuel in the baffle housing at all times. To ensure that this is the case, even when an empty tank is topped up with a small quantity of fuel, the fuel filler pipe -4- goes directly into the adapter plate -1- on the baffle housing. In this way the fuel is always supplied directly to the fuel delivery unit.

Re: The new fuel pump should have fixed the problem, assuming.....
 

Well,
i had the car towed from that mechanic to the dealer. after taking out the new pump and investigating i got a call today saying that they needed to replace the fuel sending unit(s). total cost $750. he says the car is reading gas in it but the tanks are empty. i exlpained to him that the car has stalled within 100 miles of being filled up. i read here that the sending unit malfunction could cause stalling even when only a 1/4 tank low. could this be it?

thanks
bobby

Re: Fuel delivery issue
 

I seem to be having this same problem...did yo find a solution to this as yet?