snocrazee

Wife called yesterday and says the Audi died. She got the car back home and it died in the driveway again. I came home and it started right up and then died after about 20 seconds. Checked fluids and charged battery overnight and the car will still start and then sputter out and die after about 10-20 seconds.
I scanned it and found no fualt codes for engine. After a little research on the forum I think I might need a main fuel pump.
So my question is from my understanding the transfer fuel pump kicks in during starting and heavy loads while the main fuel pump should be running continuously. Is this correct and would that explain why the car dies 10-20 seconds after started because the transfer pump kicked in and when it shut off there was no fuel being supplied by the main fuel pump?

2004 Audi A8L
about 90k miles I think...

Thanks in advance...

mishar

Why don't you start with fuel filter.

s4master1

that is actually very accurate diagnosis,
is very easy to check if you suspect the main pump, disconnect the right side pump (passenger side in US), and if the car starts and runs for 10-20 sec is your main pump.
now if in doubt still plug back the pump and unplug the driver's side unit, car will not start at all.
good luck.

UkiahA8L

I had the exact same problem 2 years ago. Dealer had it for over a week before recommending new pumps. After replacing both pumps I've never had a problem.

Eric04D3A8L

This exact situation just happened to me 2 days ago.
now the car is at the dealer for 115k service (including the timing belt etc. jobs), the car stalled once before going into the service bay, but my service rep said as soon as they put the car on the lift, they started her up again to try to isolate which fuel pump is problematic. But the weird thing is it kept on running for a good half an hour. They said as long as it doesn't shut off, they don't know which pump is faulty. should i tell them to replace the main pump anyways? Do you guys think it will act up sporadically again like this?

mishar

I am not sure where are you guys finding information about the fuel system and the pumps, but they are in discrepancy with Audi SSP 282. As it is explained there both pumps are working all the time, so if only one is OK car should run at least on the strait road and idle for sure without any problem. So if your car stall because of pump problem you should change both of them.

Next think is that "transfer pump" and "main pump" terminology. Right side pump use it's pre-stage for powering suction pumps that transfers fuel diagonally to pump reservoirs in order to prevent dry run in curves. So the right one is in charge for the transfer not the left one, but it doesn't make it any less main since its main stage is pumping fuel to the engine just like the main stage of the left one.

DA8

Mishar,

I respect your knowledge and you have much valued post in this forum to me. But you are wrong about this. My understanding comes from experience of actually reading every publication I could get my hands on including the one you are referencing and the Bentley, and others. But mostly from having the problem and diving into the tank. The right side pump is the main pump and it runs 100% of the time the car is running. The left side pump is the transfer pump and it runs at start up, while transferring fuel to the right side of the tank, and at high loads. There are two lines from the left transfer pump that feed into 1) the top of the housing for the main pump, and 2) into the fuel feed line through a Y connector which has the other side coming from the main pump.

Examination of both pumps changed out at the same mileage interval reveals heavy deposits of tank scum on the main pump bottom plastic mechanical filter and light deposits on the transfer pump bottom filter.

Suction pumps at the bottom of the tank are in physically enclosed areas so they always have fuel even at cornering, but the main and transfer pumps themselves also are inside of a housing that is filled with gas constantly regardless of cornering. When you pull out the pumps you have to invert them and dump their contents back into the tank because the housings are filled but do not expel fuel.

The car will not run with the main pump out. If you doubt me pull relay 614 from under the front passenger foot well and you will mimic main pump failure. Or you could probably pull 20A fuse 31 from the right passenger dash (with door open) and achieve the same results. The car will start because upon start up the transfer pump will operate for 20-40 seconds. But for some reason the transfer pump shuts off after that leaving you with no fuel pressure. Apparently the transfer pump does not "compensate" for the main pump when it is not performing it's function. The two pumps both have their individual functions and if one is not working (especially the main one) the system does not operate properly or in the case of the main pump being out at all.

This is not just my experience, but quite a few others have had the same failure.

mishar

Thank you for the prompt reply. I've red carefully all this in your previous posts, but, as I said, SSP 282 says differently. I don't have my own experience with this. If I do I wouldn't need to ask. I just wonder if this system was changed in the mean time so that you are actually right. If not, than right pump, actually its prime stage, is transferring fuel from left front part of the reservoir to the right pump reservoir and from right front part of the reservoir to the left pump reservoir by powering Venturi suction pumps.

On the other hand it seams to me that you are right about 30 seconds timing of the left pump at the start for faster pressure buildup. Turning it off at the low engine load is logical. Turning it on again on the high engine load would be too. That would explain difference in the filter state. I am just a bit puzzled how they missed to explain that in the mentioned SSP. Than again it is translation from the German original written by some pen pusher.

P.S. If this is right than I am wrong about necessity of replacing both pumps at the same time. As you said there is some money to be saved.

DA8

There is money to be saved by replacing only the right main pump if you are only planning to own the vehicle for a bit, but I still think it is good to replace both if you plan to own it for a while.

A) Transfer (left) pump will fail at some point and may not give you as good an indication of what the problem actually is because car may still run, just with problems.

B) Once you have bought the lock ring tool and have become acclimated with the process and have the trunk torn apart and have 1/3 tank of fuel in there which is highly recommended, it is an easy task and time efficient to just change the other one.

I think it is worth the extra $257 for the transfer pump. All things considered. Now I am not going to worry about being stranded by fuel pump for another 100K. I just have to replace the fuel filter every 30K or so.

mishar

I believe there is something not really cleared up in this discussion. Transfer pump. Left pump has nothing to do with the fuel transfer. That's part of right pump functions. That is clear from the schematics of the fuel system. Just follow the arrows indicating the flow. English text there is not perfect. They are mixing sides and terminology. Same think is with ELSA English version. I guess somebody made a mistake translating it.

Initial 30 seconds of left side pump operating (together with the right one) is there in order to prime the system and build necessary pressure ASAP. 30 seconds of transfer wouldn't make any sense. If you keep driving under 3000 rpm for a long enough you would burn all fuel from the right side of reservoir and since the left pump was never on fuel from the left side of reservoir wouldn't be transferred to the right.

Why do I think this part of knowledge is important? Well if we know exactly how this works we might be able to help ourselves if our car dies for the reason of broken right pump (like yours did) in the middle of nowhere and our mobile phone is as good as a calculator. We can simply rewire right pump wire to the left pump (probably with some extension) and drive back to the civilization. We may even be able to use our cars while waiting for the right pump to arrive. Only think we must do would be keeping our reservoir fairly full because transfer suction pumps wouldn't work.