Bad gas... in my Audi A8L
 

Thanks to all for contributing to this thread...

My wife filled up the 04 D3 4.2L with 93Octane at a station where a big tanker was filling up the underground storage reservoirs. That's a recipe for getting badly contaminated gas and then...

Later that same evening I was on a 50 mile drive and the car was gasping for something (gas or spark) and would not accelerate and speed dropped to no more than 20mph and eventually would stall. Would immediately start again and go for a bit then symptoms return and eve ntually stall.

Next day it ran better so I drive 11 miles to train station and it stalls. Tow it home and since then it won't run more than 30-40 seconds. Starts in an instant with no waiting after it stalls.

Replaced fuel filter, starts easily and it ran for about 3-4 minutes then it reverted back to not running more than 30-40 seconds then stalling.

I checked VCDS for DTCs and measured fuel system performance but I don't see anything to suggest what specifically is wrong. I must add that I'm not an expert on what I should be looking at so I may simply not recognize the obvious in VCDS.

Well, what say you to this info? Got any ideas?

Sounds like a bad fuel pump at first reaction
 

Let others chime in who have been through it, or search the archives, but that dying after initial start description sound like one of the tank fuel pumps to me from prior posts I've seen on the subject.

The fuel pump is bad if it runs about 30 seconds then dies. There is a good thread that we posted about this a while back. It was really "interesting" driving it to a friends shop for him to look at it with the engine only running 30 seconds at a time. My pump only lasted 90K and after it was replaced I played around a bit with the bad pump and got it to continuously spin. I think they suck up debris in the tank and it gets gummed up in the pump.

This. Ended up being a huge pain in the ass on my A6.

Incidentally I bought the very same mann filter off amazon, will be putting on the S8 whenever we get some nice weather.

Long overdue reply - I've been flying around the planet too much!

Diagnosis - Right Side Fuel Pump had been shorted out by mice who took up residence on the right side fuel pump access cover. The fuel pump wiring and fuel lines attach here.

It was obvious after removing the metal covers in the Trunk compartment. A perfect bed for mice made of insulation was packed in amongst the wiring for their comfort. What confirmed it as a bed for mice was the excrement ( mouse turds ) in their nest. Rodent threats are not discussed in any Audi repair manuals, however, Audi wire insulation is a favorite medium for rodents to sharpen their teeth. The exposed wire had evidence of rubbing on the metal cover ( front right of trunk compartment) and eventually shorted the circuit.

Steps:
1) Checked FP Relay - OK
2) Checked circuit continuity, voltage level, resistance level - OK
3) Removed pump assembly and tested pump motor - DEAD.
4) Order replacement pump from online - retailer. Audi Stealer price was $900+ Online price was $390 but had to wait 6 weeks to get it... bad timing as Bosch was short on supply to their wholesalers. This wait is not typical.
5) Test new pump motor prior to install - OK
6) Install
7) Fill tank 1/2 and run function tests and set Readiness codes (Ross-Tech)
8) Drive with smile until 1/4 tank of fuel then realize something isn't right. Realized this was 1st time fuel tank was this low since repair. Add gas - problem goes away. Hypothesis - fuel lines are routed incorrectly or suction hoses were disturbed during repair (too high in tank to suck fuel).
9) Check fuel line routing INSIDE tank and correct.
10) Close up tank
11) Test car / function tests and set readiness (Ross-Tech). Setting Readiness using Ross-Tech tests fuel supply system but doesn't test for incorrect hose routing.
12) Drive car with smile again... several tanks of fuel with no problem.

Special Note 1) When reconnecting fuel pump hoses, be sure to route the hoses correctly... per image shown in the repair manual!! The design of the hose connectors prevent incorrect connections, but do not prevent routing the lines over or under another line and that is critical. It may not seem like it would make any difference but it certainly does!

I had the manual as a reference but didn't sufficiently respect the image showing the lines connected. Consequence: was while driving in Chicago the car was stalling regularly when the fuel level dropped to about 1/4 full.

Test your repair by driving the car locally down to near empty fuel level. If no problem then you're good! Otherwise... RTFM carefully and try again.

Special Note 2) There are many other sources of failure to consider if you have fuel supply issues. Even if primary fuel pump (right side) is mechanically/electrically sound itself, the source can be elsewhere. Follow diagnostic steps carefully and use common AND uncommon sense.

If you unexpectedly discover bare wires on your fuel circuitry then consider this in your diagnosis steps.

They've had this same stupid design for awhile. I just did my A4 filter. Only it is more dificult to get at. The nut started spinning in the plastic. I used a Dremel tool to grind the head. I was trying to take it easy so as not to melt the plastic, so I could reuse the bolt hole. ...it melted through anyway. Now it's held in with tyraps.
Why didn't they use brass or stainless for this??

Pics of open fuel filter
 

I just Changed my FUEL FILTER on my 2009 A8L 4.2L at 82,700 miles on the odometer. No reason why, just did it since I was ordering other parts. Put WD 40 on the retaining triple square bolt threads and let it sit for 10 min. It came off with a snap, so there was some rust there, but luckily it came out... coated it with anti-seize when replacing.
There was very little sediment in the fuel which i drained.
I sawed open the filter (see pics). The filter element was pretty clean, with no sediment or gunk on it. The tan color was the same on the inside and outside of the element, so it is not a layer of dirt. It is nice to have it changed, but I probably could have waited till 100k miles. Anyways, I guess that's how preventative maintenance works. I replaced it with an Audi one... for something i will change 2x in the life of the car, may as well spend another $10. Hope this helps guide people as to when to change it.

I've replaced the fuel filter every 50k miles on both my 4.2 and W12. The W12 after I bought it at 54k actually was pretty clogged, could barely blow through the filter element. Cheap filter and fairly easy DIY. Too bad newer cars like my S5 have the filter in the gas tank itself.

Just done this job today on a 2009 S8. 125k miles. It was the original filter. Same issue with the ceased / rusted bolt. I used a cutting disc on a dremmel to cut the bolt out (do this before fuel lines are disconnected otherwise sparks might be a big fire risk!). Otherwise everything was exactly as described in the posts above. I am glad I did this as there was a lot of back pressure on the old filter.

Im about to do mine ~ will report back with my filter condition. Very curious to find out the condition, since mine is 175000KM ~ I highly doubt the previous owner replaced it.