DA8

I am not really sure what is meant, "is in charge for a fuel transfer."

There is a path for fuel. Main (right) pump runs all the time and feeds the filter/fuel line to the engine. With both pumps working, secondary transfer (left) pump feeds fuel into reservoir located on front vehicle side of main (right) pump. Main (right) pump feeds that fuel and fuel it is sucking from the right side into the system.

Purpose of secondary transfer (left) pump is twofold: 1) to supply more fuel under higher demand, and 2) to transfer fuel from the left side of the tank to the right side of tank.

Since main fuel supply is always being drawn from the right side of tank by main (right) pump, the right side of tank level gets lowered by fuel consumption. The tank is not a square vessel without obstruction that self levels. Rather it is a two sided shape that wraps around the spare tire and has a lower section on both sides. The secondary transfer pump serves a 2nd function of transferring this lower fuel from the left side of the tank to the right side of the tank to keep both sides level as fuel is consumed.

mishar

Yes, but it is not left but right pump doing all that. Otherwise it won't work at all since the left pump is working just occasionally.

Here is the picture:

ayrula

I agree south you gentlemen, however I took this from the service guide Mishar posted.

the fuel pump G23 (left) conveys a maximum volume to the pressure regulator at the fuel rail to achieve short starting times.

One of the main purposes of the left is to achieve short starting times as it helps build fuel pressure quicker. I don't have the delayed crank if I shut off and restart lonly when sitting and pressure is lost. Wouldn't the clogged or dirty filter slow flow slightly delaying crank?

In many of my searches for symptoms of partially clogged filter I am seeing delayed starting times. If the left pump was out wouldn't I have delayed start every time as the right pump would be the only side feeding fuel and building pressure at a constant rate every time?

DA8

Ayrula,

I just don't find it likely a dirty filter is slowing flow to reduce pressure at startup. I think it would just create more resistance for the pumps, but the pressure and flow will still be there. I sawed my dirty filter in half after 100K of use to inspect it's condition, since the manufacturers claim no change needed ever. When I inspected it I found it to have the paper/fiber ellement inside turned black. There were no large blocking particals, just a dirtyness of thousands of minute particals. I'm pretty sure it still flows, just that it offers more resistance to the pumps, wearing them out faster.

Theoretically, although I have no experience with this , another thing that could stop flow would be large particles caught in the pre-filters of one or both pumps at the bottom of the tank. If the secondary transfer (left) pump were plugged up, even though it is working at startup, the fuel would not pressurize the system sufficiently if fuel were restricted at the pre-filter for the secondary (transfer) pump by larger particles plugging it up.

But still, I think it never hurts to change out your fuel filter, and who knows maybe it will solve your problem.

I think you are correct that the secondary transfer (left) pump supplies extra pressure for quick start. Thus if long crank is your problem that would be a worthy suspect area, having already confirmed spark is not the problem.

Mishar,

I am not sure where there is confusion, as I said before, other than confusion created by trying to understand the system from studying Audi SSP literature that is VERY inadequately written but has nice pictures.

Secondary transfer (left) pump pumps fuel over to the main (right) pump from the left side of the tank to transfer left side of tank fuel for leveling purposes since fuel is always being depleted out of the right side by the main (right) pump. It is actually transferring it to the right side of the tank into a small reservoir located on the front side of the main (right) pump. The only difference between the two pumps is hose lengths, electrical connections, and this reservoir added to the housing in a clip on fashion to the main (right) pump. When the right side of the tank gets lower and needs fuel, the secondary transfer (left) pump pumps fuel into this reservoir on the front of the main (right) pump. Fuel overflows out of the reservoir on the main (right) pump until the right side level is equalized.

Main (right) pump is simply always pumping into the fuel filter and engine as long as the engine is running. There is no transfer function in the main (right) pump except transferring the main fuel supply to the engine. The secondary transfer (left) pump feeds the main (right) pump which feeds connections out of the fuel tank to the fuel filter then the engine.

I have tried to clarify the issues for everyone by accurately labeling the 2 pumps:
-Main (right) pump
-Secondary transfer (left) pump

mishar

Once you turn the engine off injectors are closed and pump stops. There are check valves at each line and pressure regulator on the other side of the line. So line and filter are under pressure for quite some time. After some time small leaks here and there (within the system) drop the pressure, but fuel doesn't go anywhere. It is only small amount of fuel needed to build up the pressure. As I said, filter clogged so much that such small amount of fuel can't easily go through would be a big problem later when gallons have to pass.

Than again, replace the filter and see. It is good anyways.

crisseibert

so please tell me . my Audi A8 2004 was e just like this problem and i figure if only one pump its work …... and i had 45 miles gas on the tank ever time i start up the car die after 20 seconds i bought 3 gallon gas put inside the tank ..i had 75 miles and the car works fine . so the way i think only one pump work ..whay the car has to be 75 miles gas to work?… because only one pump work?

mishar

It looks like something is wrong with transfer of gas from left to right side of your reservoir. Part of the right pump is in charge for that, but it may be some hose inside the reservoir.

chadthede1

I have an '01 A6 with the 3.0L and have had trouble with it starting. It will always start but you have to crank it over for several seconds before it starts. Sometimes it runs rough for 2-3 seconds and then smooths out. Sometimes after a few seconds of cranking it will fire right up and idle smooth. I don't have any issues at high RPM so I don't think it is a fuel filter issue. I didn't think it could be a fuel pump either until I read this forum. Does my car have the same dual fuel pump system?
If it does, I suspect my driver side fuel pump may not be working correctly. I will have to put my head in the trunk to listen for it while my wife starts it sometime. Should the pump kick on as soon as the key is turned on or does it wait until you start cranking?

mishar

I am not sure about A6 configuration but it is probably similar. If it is so you should lift your trunk carpet and find out which pump is working or not by unplugging them. They start the moment you start cranking. Could be a fuse too. They are close to the battery. Again, if it is like A8.

sferrazjr

Hello guys!!!

I got the exactly the same problem in Audi 80 Avant 1995 2.6 V6, engine ABC.

I was driving it normally when suddenly the engine stopped working. Is starts again but after 20 to 30 seconds it dies. I tried keep high revs but it didn't work, it dies anyway.

The fuel pump is new, I changed it almost 2 years ago but drove only 10k kilometers. When I had to changed it the car won't started at all.

I also changed ignition switch 3 months ago. It worked fine so far.

I've being looking on internet what might be, but this is the only case so far that is similar to mine, although in a different Audi.

Anyone here that knows the B4 plataform?