ezveedub

Yes, that should work, but keep in mind, you can only do this for a short period. The left side tank will run out of gas, leaving fuel on the right side. You would have to keep filling the tank to get the vehicle to run for longer distances.

bcvickers

To light up an old topic and throw a bit of a wrench into this discussion, in the parts book for our cars here: http://www.audiusaparts.com/parts/20...=FUEL%20SUPPLY and numerous other parts books I've looked at they call out "upper" left and right pumps as well. Could these be the actual transfer pumps activated by the independent fuel level sensors on each side? It seems ludicrous but so does most of this fuel system really.

In addition I'd like to point out that I order Bosch part number 69809 from a yet to be un-named vendor whose website said it was an exact match for my car. It looked good until I got it out of the box and found that its connections were swapped on the pump section and it had an extra female connection on a small tube. Overall it looks like the 69809 and 69808 are probably not for these cars at all, or maybe a newer model?

mishar

Both pumps should have two stages:

DA8

There are some small pre-pumps, I think they call them suction pumps, in the bottom of the tank that feed into the 2 electric pumps. That could be what is being described in parts manuals as "lower pump," but I would just ask the dealer for clarity on what is in the manual. Those parts manuals are not very clear a lot of the time. That is one reason why whenever you order parts from a dealer they want to know your vin number.

Both main pump and secondary pump are essentially the same pump with slightly different housings and hose connections. It could be that the Bosch aftermarket pump is manufactured to sell one pump that converts for either application. Just a theory.

It is a confusing thing to understand until you dig in the tank, compounded by varying terms and part descriptions for the 2 different pumps and misleading SSP282.

bmwm750

Since my car is still on its original pumps, and I'm coming up on 120k, I think I may do this as preventative maintenance soon.....

Seems both fuel pumps and filters would be the way to go to call this done and never worry about it again.

Vicl

Bmwm750! Fuel filter replacement should be a good preventive technique. Replacing the fuel pump is relatively costly and not fun job at all. I had to do that on my Audi V8, 3.6 PT, 1991. Going inside in the trunk and breathing the gas evaporating is not fun at all! Beside it I managed to drop one of the steal tools in empty tank! I was lucky it didn't explode
Anyway, changing the fuel filter takes 15 min and does not require some specific tools or knowledge. It is locked by clips. You just push the clip in (in my case that’s what I did) and it releases the lock.
I do replace the fuel pump every 50K KM (about 31K Miles). The filter is not expensive ether.

Good luck!

ltooz_a6_a8_q7

Now, why does a fuel pump have to be so complex? I haven't had any problems with the pump, but I really like to understand the whole "over engineering" on these fuel pumps. Are there articles about the reasons behind these designs that I can read? I'm sure there are amazing explanations on these.

Thanks,

Louis

mishar

Reason for so complex system is shape of the tank. It is basically two tanks connected on the top. In order to reach all fuel at all times they have designed it this way. Secondary pump is only for a faster fuel pressure build up at the start and sure supply under high loads. It is all here.

ltooz_a6_a8_q7

Thanks Mishar,
Good readings.

Cheers,

Louis

DA8

Just a few reasons,

Full size spare tire, maximum trunk & backseat leg room squishes tank into horizontal and vertical layout separated by tire.

Tank is weird 2 sided shape that has to get fuel from one side to the other all the time to maintain center of gravity.


When low on fuel tank needs to be able to get fuel from lower part of tank to main parts of tank where fuel pumps are to get last drop.

Sporting quick changing motions of the car need to be able to maintain fuel supply in strangely shaped tank.

Large variance in fuel consumption due to efficiency of A8 at normal driving and high fuel demand needed in massive acceleration with secondary air chamber in intake manifold opened. Probably difficult to maintain constant pressure with changing velocity in fuel supply.


And regarding changing the pumps, it is not that hard, but it is awful with the fumes. I recommend a respirator with organic cartridges. And there is the fire hazard.

But one reason to do it preventatively and one reason only: when the pump goes out, you will be stranded. And it will go out. If you are OK with that don't sweat it.