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Discussion Starter #1 (Edited)
Just want to compare notes as this is likely a problem encountered on both Audi and VW vehicles

Vehicle:

I have a 2004 A6 2.7t S-line sedan ... 156,000 miles (automatic) ....

A little background:

last year around this time, the car couldn't be started. I put a stethoscope to the fuel tank under the seat, and there was no noise while the car was trying to start. Assumed bad fuel pump, so I replaced it (tank was completely full ugh). Car started and has been running ever since.

Current Problem:

Recently, the new(ish) fuel pump has developed a high pitched whine during warm-up. It goes away after about five or ten minutes of run time ... until the next morning, when it whines again.

I know I have some leaky injectors because the car occasionally runs rough during warm up in cold weather (plugs and ignition coils replaced 30K miles ago). Also sometimes floods on hot days (especially after filling the tank)
Now it's gotten so bad I can smell gas in the oil and in the exhaust during warm-up. Once warm, it runs smooth (passes emissions) and runs relatively strong (esp strong as the weather is getting cooler).
It's down to 22mpg ... the car used to get around 24+mpg with my wife driving it to work.

Does this sound like cavitation due to leaky injectors and the pump having to prime the system every morning (and afternoon) ... ?

EDIT: I started noticing this noise AFTER adding Liqui Moly injector cleaner (did I loosen debris in the fuel tank? ... I've used techron and liqui moly injector cleaners (from the dealer) in the car before with no issues)

Projected Fix:

Replacement injectors (rebuilt 4 hole Bosch "upgrades") are arriving next week. I'm going to swap them out and see if that fixes the whine.

Speculation:

Could this just be a poor (short-lived) replacement fuel pump, regulator, clogged filter (its still the original one but I only run Shell V-Power and it seems to run fine on long trips)...

Thanks in advance Vortex :)
 

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Discussion Starter #2
I started noticing this noise AFTER adding Liqui Moly injector cleaner (did I loosen debris in the fuel tank? ... I've used techron and liqui moly injector cleaners (from the dealer) in the car before with no issues)
It seems like after the Liqui Moly worked its way through the tank, the fuel pump whine stopped. So far, even as the weather turns colder, and the car has sat for as much as a week without being driven, it seemed to start and run without stumbling. I received the injectors, but haven't replace them yet. So it seems to be running good on the original injectors. Looks like either a fluke, or Liqui Moly was working hard during that tankful of gas. Anyway, will keep the post updated to see if the gas mileage now improves over time. I'll still probably replace the injectors if the gas mileage doesn't start coming up a bit.
 
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