This is great stuff.
Ill let you know how we get on with the salvaged assembly.
J

 

Hi, I have a bad pump, doing research. There is only one fuel pump that works in an A8. Other look like they will, but alas, they won't. Since you are in the UK, check this out. (I still need to order one for myself.) If you got a different part number, that is the problem. Well documented here in the US.

This fuel pump is NOT available in the U.S. it is available in Europe. I purchased mine out of England. Here
http://www.ignitioncarparts.co.uk/de...P405052002001Z

 

So i finally got her back.

It turned out the original replacement pump was at fault. It was an ebay listing and claimed to be the real thing and looked identical. It picked up fuel from the cup and sent it to the rail but didnt produce enough power thru the auxiliary port for the jet pumps at the bottom of the tank. Had a terrible bum steer from audi who said it was a problem with the tank into the fiasco. I bought another pump from ignition parts and it worked perfectly.

I have sent the pump back and it has to be tested by the german supplier. I would like to know what the psi should be for that tertiary port. I know the send and return should be 4bar 60psi. Im making a point of pursuing that refund out of principle. Anyone have that data?

Anyway , shes back on the road and after a small valet that car seems to drive better than ever. Ive driven some crazy cars over the last six weeks including an 84 mercedes 280e , a 91 chevy s10 pick up (which was particularly brilliant ) an alfa romeo spider and a brand new honda civic. i have to say it has been fun, but driving the A8 again today made me appreciate what ive got there. Simply one of the most elegant cars ever built.

Thanks so much for all the feed back.

I feel ive attained an intimate knowledge of the fuel delivery system and hope never to smell petrol again!

Stoosh.

 

If anyone has the patience to explain this to me, I could use the knowledge. I'm in the middle of diagnosing a similar issue, and I'm about to remove the fuel pump. Until I read this thread, I was thinking that if I need to do something temporary, I could use any generic pump to get the car running.

-----------
"At first we thought it was the well documented problem of the assembly not being seated correctly and therefore not giving drive to the jet pumps in the bottom of the tank that lifts fuel into the cup...

It turned out the original replacement pump was at fault....
...It picked up fuel from the cup and sent it to the rail but didnt produce enough power thru the auxiliary port for the jet pumps at the bottom of the tank..."
-----------

So it sounds like it's not as simple as a pump sucking fuel up thru a hose and pumping it to the fuel rail. Without seeing it apart, I'm having trouble understanding the relationship between the fuel pump, the cup, and the jet pumps that all seem to be vital to getting fuel to the engine.

 

Hi mate,

Im shady on some areas too but the way i understand it is this-

The pump is fits into the pump assembly (the big plastic white blob ) which is then seated in the "cup" . The pump has 3 ports on it. The top one sends to the rail and the larger of the bottom ones picks up fuel and sends it to the top. The other bottom one sends fuel down to the bottom of the tank. That jet of fuel drives some little pumps at the bottom that in turn send fuel back up to the cup assembly and fills it up.

My problem was that i had the right pump but the unit was faulty which led me on a red herring hunt.

Get the right pump like the one shown in an earlier post on this thread. follow the ignition parts link and get one shipped.

All you have to do then is get the assembly out (which is rather involved) swap out the pump and reinstall it.

ive attached a few photos that ive collected from here and other places.

Hope it helps.

 

Wow... that is a crazy set up. What happened to the days when a temporary hose could be slipped into a can of gasoline to start up the engine?

I've always wondered how the tank is designed so the car can drive up a hill with the gas gauge on empty and not run out of gas. On a side note, I was pleasantly surprised to find out the A8 will run for 25+ miles even after the "miles to empty" display has gone to zero. The day I bought my car, I was out of state and got on the highway in Utah with under 1/4 tank...and soon discovered that the next gas station was 100 miles away. :-/ And made it with no problem.

Thanks for the explanation and the pics. That's a big help! I can't wait to take it apart. (not really)

I have one other question about the assembly. you mentioned this long bolt and something about a note in the Bentley guide. What is that issue about?

If you have a chance, can you post the description section for the numbered parts in the diagram?

Thanks again!

 

One more thing... Will the fuel pump be able to pump gasoline if the return line is not working?

When doing some tests, I removed the fuel filter and ran the pump, and only got a little bit of gas out of the line. With no return line in the path, does that mean there is no fuel available for the pump to pick up? Could my original problem be the FP regulator, or the return line...preventing no fuel from reaching the cup and none available for the pump?

 

My car screams for fuel and says I can go no further, and then will only take 20 gallons but I think this a fine thing. Running one of these pups dry is some bad juju so the best thing is to never run it so low it starts to suck air.

As for the return line, I do not think the return line is needed for the pump to make pressure at the fuel rail.

-Joel.

 

Stoosh:

What was wrong with your bad pump? Did it not run when squeezed into place or was it an output problem or?

I reckon I should change my pump before it leaves me stranded some fateful day and I'd like to bench test the new one as best I can before installing it. I'll also be in Europe in a few months so I might bring a pump home from that ebay vendor or ignitionparts.

 

here some more pics from audi's elsawin