# Fuel Pumps - An Explanation



## steveupton (Mar 23, 2010)

*An explanation of how the fuel delivery system works and which pump to get*

_*Disclaimer - I take no responsibility for any consequences resulting from using information contained within or referred to in this guide. Before undertaking any work on the fuel system, the battery should be disconnected, all naked flames extinguished and any radiant heat sources turned off.*_

Specifically for Quattro models, there have been a few instances recently and many more since I've been on here where there is some confusion regarding which fuel pump to get when it needs replacing. Having replaced the fuel pump on my TT recently and done some research as to what is available, I thought it would be useful to put together something that explains how the fuel delivery system works, what is available and from where.

*Quattro models*

Have a fuel tank that has a tunnel in the middle because of the prop shaft, Haldex and differential. There has to be a mechanism therefore to draw petrol from both halves of the tank and this is achieved by fitting a powered pump in the right half of the tank and a suction jet pump in the left half of the tank that is powered by fuel being sucked through an interconnecting fuel pipe linking the 2 pumps. There is a further fuel hose from the suction jet pump that then transfers fuel from the left half of the tank to the right half of the tank adjacent to the powered pump.

It is usually the powered pump that needs replacing and common symptoms of this are:-

1 Excessive noise

2 Failure to prime the fuel delivery system to the correct pressure. This can sometimes be overcome by leaving the ignition on for longer than normal before starting.

3 Complete failure, in which case the engine will not start at all.

In the event of a complete pump failure, even a scan with VagCom, VCDS or a VAG compatible scanning device may not produce a fault. It is therefore desirable to replace the pump if it becomes noisy or takes a while to prime the system from cold.

There are 3 options:-

1 Replace just the powered pump, otherwise known as the swirl pot, that is only manufactured by Siemens-VDO. This will require re-use of the existing top flange and fuel sender. This part is now available from many motor factors such as ECP and Carparts4less and can be had for around £170.

2 Replace the complete powered pump assembly that comes with the fuel level sender and top flange, available from Audi/TPS only. Cost approximately £280 including vat from Audi as at 31/12/13.

3. Replace the powered pump and suction jet pump assemblies complete with fuel level senders and top flanges, available from Audi/TPS only. Cost approximately £380 including vat as at 31/12/13.

Please note, pumps are not available from Audi without the fuel level senders or top flanges.

Replacing the fuel pumps complete with senders and top flanges is a relatively simple operation and the following guide explains the procedure very well:-

http://api.viglink.com/api/click?format ... 6493942358

In addition, if replacing just the swirl pot, the 2 pipes A and B indicated in the pic below will need to be disconnected from the old swirl pot and connected to the new. This is not as easy as it sounds as the pipes are a shrink fit, a good tip is to inject a small amount of washing up liquid between the pipe and spout using a syringe. Patience is of the essence here because both pipes must be kept intact.

A new clip will be required on the pressured hose B as the existing one is single use. Also transfer the fuel sender, connect the fuel pump power leads, arrange the pipes the same as they were and zip tie in the same locations.










*FWD Models*

The fuel delivery system for 2 wheel drive models is much simpler in that the tank is not split into two halves and there is only one electrically powered pump. Replacement pumps are now available from most motor factors considerably cheaper than from Audi.

*AUDI PART NUMBERS*

*Quattro models*

Complete with fuel senders up to August 2002, chassis No 8N-2-030000

8L9 919 051 G (powered pump)

8L9 919 673 J (suction jet pump)

Complete with fuel senders from August 2002, chassis No 8N-2-030001 onwards

8L9 919 051 J (powered pump)

8L9 919 673 P (suction jet pump)

Seals are not included but it is good practice to replace them and the part number is 321 919 133

*FWD models*

Complete with fuel sender up to August 2002, chassis No 8N-2-030000

3 bar pressure for 150 bhp models 8L0 919 051 H
4 bar pressure for 180 bhp models 8L0 919 051 J

Complete with fuel sender from August 2002, chassis No 8N-2-030001 onwards

3 bar pressure for 150 bhp models 8L0 919 051 N
4 bar pressure for 180 bhp models 8L0 919 051 L

Please note that none of the above FWD pumps have a take off that can be used to power the suction jet pump fitted to the Quattro.

*OTHER SUPPLIERS*

The 4 bar swirl pot for quattro models is available from various factors, for example ECP and carparts4less, the pic below shows what it should resemble:-










Note the flexi hose take off with the black union, this connects to a pipe going to the suction jet pump in the left half of the tank.

There are two pumps available, up to August 2002 chassis number 8N-2-030000 and post August 2002 from 8N-2-030001, same as the Audi supplied pumps.

For FWD TTs, there is a Pierburg pump available that is a direct replacement for the original VDO pump at a considerably lower cost than from Audi. Again, there are different ones, the same years and chassis numbers as above apply.


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## tadope (Oct 20, 2020)

Hi. Is it possible to modify a fwd pump to run a quattro tank?
Either by tapping and adding a fitting to the electric pump itself. Or splitting the out line with a T ?

Many more purchase options with fwd pumps than 4wd just because of that little extra nipple.


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