wjharrison

A local shop replaced the fuel pump on my 2000 A8. Now, when the fuel tank reaches down to about 1/3 full, it acts like it's running out of gas. It hesitates and loses power. I'm going to change the fuel filter tomorrow, but does anyone have any ideas what else it could be?

skiracer

won't get pumped into the section with the fuel pump. The A8 gas tank is very complex, and the only way to get fuel from one side of the tank is to pump it. The fuel pump uses high velocity fluid and a venturi to suck the gas from the far side of the tank to the side where the main fuel pickup is. If the shop didn't properly attach the "suck" lines, then you will run out of gas at ~1/3 tank remaining.

PaulW

If you need me to look it up, just ask.

wjharrison

Thanks so much for the troubleshooting doc. You wouldn't, by any chance, have the Bentley R&R instructions for the pump, would you? It starts on page 20-17.

JHLAudi

A8 Fuel Pump Replacement (what the manuals don't tell you)

I also had my dead A8 fuel pump replaced only to run out of gas at 1/3 tank as may other posts have noted. Two subsequent visits back to my Audi garage did not fix it so I decided to look into it myself. Replacing the A8 fuel pump properly is a difficult job to do since you need to make two connections simultaneously without being able to see them! Following the manuals only gets you so far, problem solving on my car led to these steps which allowed me to fix my car:

1) CHECK IF YOUR FUEL PUMP IS INSTALLED PROPERLY: Remove the fuel sender from the fuel pump assembly. Using an inspection mirror on a 16" extension and a flashlight, inspect how your fuel pump is aligned with the base of the internal tank reservoir. If your fuel pump is installed properly, there should be a 2-4mm gap between pump and "funnel" on the base of the reservoir that the pump drops down into. If they are touching, that means that the fuel pump is cocked in the reservoir - likely due to the second stage output connector from the pump pressing against the side of the reservoir instead of into it's associated connection. If the long fuel pump bolt is torqued to spec in this misaligned condition, it is possible to crack the reservoir housing! More on that later.

2) ALIGN THE RESERVOIR: remove the left (drivers side) fuel level sender from the tank and you can reach into the tank and by grabbing the two hoses coming from the reservoir to the left tank, you can position the reservoir to mate with the second stage output fitting on the pump.

3) DRY FIT NEW PUMP INTO RESERVOIR: After many unsuccessful attempts to mate my pump with the reservoir I decided to remove the reservoir to see why I could not do it. To remove the reservoir, release the 3 quick disconnect lines from the front of the reservoir and the one to the left tank, move the fuel filler tube out of the way and remove the reservoir from the tank. Try assembling the new fuel pump into the reservoir - I found my new fuel pump (same Audi PN as the old one) would not fit together without forcing it! The OD of the pump was hitting the reservoir side preventing the second stage connection. I suspect that this may be the cause for the many other posts on this topic. Using a hair drier (BE CAREFUL OF GAS FUMES), I softened the side of the fuel pump housing in the problem area and deformed it eliminating the interference. The new fuel pump now slips right into the reservoir connections.

4) CHECK THE RESERVOIR FOR LEAKS: If the reservoir has a crack it can leak fuel into the rest of the tank resulting in hard starting after your car has been parked a while. While you have the reservoir out, assemble the pump into it making both fuel connections and tighten the long bolt attaching them together. Fill the reservoir with water which will fill the pump housing and let it stand for a few hours looking for leaks. If you have a cracked reservoir (I did not) you may be able to order one from the dealer but it also may only be order-able as part of the $1300 entire tank assembly - ouch. If so, you might try adhesives or a gas proof sealant instead. The Eastwood company www.eastwoodco.com carries gas tank sealer that may do the job.

5) REPLACE O-RINGS: If you have gone this far, before you put it all back together, it might be a smart move to replace the o-rings in the 4 quick disconnect connectors. I did not but another post suggested this and it sounds like a smart idea. Make sure you use good fuel resistant neoprene o-rings.

6) ALIGN THE RESERVOIR: Having the reservoir in the proper orientation is crucial to making both the first and second stage connections to the fuel pump simultaneously as you insert the pump. I used my OLD fuel pump, removed the top cover of it (disconnect the hi pressure connection under the top, the electrical connections and release the snaps attaching the top to the body). Now cut the plastic fuel level sender opening away so that you can reach through the roughly 6 inch top of the fuel pump housing. Insert this modified old fuel pump in the gas tank and you can now reach into the tank and feel when you have made the connections to the reservoir. When aligned properly, use some duct tape and reach into the tank through the left fuel sender opening and tape the fuel lines into place against the tank to hold the top of the reservoir in this orientation.

7) CHECK FOR GURGLING: Remove the old fuel pump and install the new one. reconnect the external fuel lines and electrical connection but leave the fuel level sender out for now. Pour about 1.5 gallons if gas into the filler pipe and start the car. It should run and if you look into the fuel level sender opening with a flashlight you should hear and see fuel gurgling from the jet on the bottom of the tank just forward of the fuel pump base. This means that the second stage is pumping fuel between the right and left tanks and you are connected properly. If you have no gurgling, remove the pump and try again. Remove the duct tape from the left fuel level sender opening when done.

These steps allowed me to isolate the problem on my car and fix it which the Audi garage could not do. It did take a few hours but now I know that it is fixed and I have had no problems in the 1000 miles since this repair.