3wall

First time post. I have a 2001 A8L with 99k miles. I have followed all recommended service at the dealer, including 90k mile service, of timing belt replacement. ($2,090). Last week the car would not start & had it sent to the dealer. They said the fuel pump was bad. New pump & oil change cost $1057. Two days later, same symptons & car quit running. Towed back to the dealer. Diagnosis - I ran out of gas. Dealer says the sending unit is bad. They replaced the sending unit today, but said the gas gauge reads half tank & they only put 5 gallons in. They need to keep it another day to figure out what is wrong. When I picked the car up after the fuel pump was first installed I noticed a faint smell of gas when I opened the trunk every time for the following two days. Also the engine seemed to crank several seconds longer than usual before it fired. Anyway to my plea for help. The service manager claims the sending unit is separate from the fuel pump and I am sure they are going to say the sending unit failure is not related to the fuel pump service and plan on charging me again for a service I think was already paid for. I have to believe they damaged the sending unit or the failure is related to the fuel pump install and I was able to drive for the two days simply because I had enough gas.
Does this logic make sense? Also, does anyone have an idea as to why the gauge is still not working despite the new sending unit. Sorry for the long post

Always Overcharged

be problems.
Understand that our cars have a saddle tank with a crossover pickup hose.
If the hose is disturbed during repair this can cause problems.
The gas smell in the trunk sounds like a crack in the housing of the pump or level sender or a bad seal.
The fuel level sender may be just stuck from sitting dry.
Suggest that if it is an Audi dealer they should know how to fix but if not and have not had one to do before you have problems.
Check your email

Always Overcharged

Tried to email but got rejected: :-(

3wall

I appreciate the response. I reviewed some past posts on fuel pumps that were helpful in understanding the problem. The dealer is Audi/Porsche. The e-mail should go thru.

Always Overcharged

Went this time

PaulW

<ul><li><a href="http://members.rennlist.com/drive944/fuel_leak_repair.html">If they cracked the housing, you'll have the same results</a></li></ul>

Philadelphia A8L

that it was a malfunction of either of the two valves that control flow out of the bottom of either side of the saddle tank, one was either sticking open, or the other was sticking closed, or clogged. The way it was explained to me is once the level of fuel gets below the top of where the tank separates into 2 sections then the sending unit drains one side first, I think the larger side. When that side is drained down the valve at the bottom is supposed to closed and the valve at the bottom of the other side is supposed to open. If this doesn't occur you're left with unused fuel and the car acts as if it's out of fuel. I then got the news that these tubes and valves are integral to the tank and the solution is a tank replacement.

The sequential Audi diagnostic procedure should have shown fuel pump, sending units, etc to be good if they were!

BrianC72gt

The fuel tank has two(2) fuel level sending units. The one on the right is incorporated into the fuel pump assembly. You would need to be suffering from some form of mechanical retardation to break it. Suprised I haven't broken one yet. However, there is an internal wire that clips to the side of this sending unit which you have to fish out from inside the hole first before sliding the sender into place. A novice might not reconnect it. If you remove the cover for the fuel sender, you can slide the cylinder up and you should see a two wire connector connected to the side of it facing you.

There is also a fuel gauge all by itself on the left hand side. It looks a lot like the arm/float/valve you would see in an older toilet. The two fuel level senders (of completely different design) average out what they are seeing to give you a fuel level reading. I wonder if you can Vag com each one separately to see what signals you are getting. If the right one is at fault, it is definitely their problem.

The one that is incorporated into the fuel pump assembly is a removable cylinder with an internal float that rises and falls with fuel level.

Your problem is NOT the senders. Your problem is that the foot of the fuel pump is not properly seated into the assembly that resides at the bottom of the fuel tank. Your car stops running at just below a half tank of gas because the suction that is supposed to lift the fuel to the fuel pump cup ain't happening. There is a little pipe with an O-ring on the side near the bottom of the fuel pump assembly. If this does not seat into the little "Foot" in the bottom assembly (which connects to the network of suction hoses that run along the bottom of the tank - think octopus), then the fuel does not get lifted up into the cup which feeds the fuel pump. The top of this cup is - you guessed it- at about the half full level. Your gauges are telling you still have fuel when the car dies...because you do. The pump is not properly seated causing you to "run out" of gas when the tank still has just under half a tank.

Also, the faint smell of gas, if we are taking bets , is coming from the fuel guage sender that is incorporated into the fuel pump assembly (right side). The little round cover for the cylinder like sender is a tight little bastard to get back into position. (a drop of oil on the O-ring helps) There are two corresponding triangle like points taht line up when the little white cap is completely seated. If they are not lined up, it is nopt fully seated and you will get fumes.

Links to my various fuel pump sagas follow:<ul><li><a href="https://forums.audiworld.com/a8/msgs/134668.phtml">https://forums.audiworld.com/a8/msgs/133400.phtml</a></li></ul>

BrianC72gt

https://forums.audiworld.com/a8/msgs/133400.phtml

https://forums.audiworld.com/a8/msgs/124049.phtml
Photo of fuel tank innards. Item 4 is the hose from the fuel filler which primers the baffle. The Big Arrow just to the left of item 4 is the part the fuel pump assembly must plug into to suck up fuel from the bottom of the tank.

https://forums.audiworld.com/a8/msgs/123645.phtml

A really bad fuel pump story (mine) Add to the parts list 8 new coils and it has been running fine ever since.

Good luck,

Brian C.