The fuel pump on the CQ is located inside the tank (yup, submerged in gasoline!), while the sedan's is underneath the car on the driver's side near the filter. If you hear a high-pitched whine from the trunk area, that's your fuel pump running. They all make some degree of noise normally, but if you notice a drastic increase in the amount of noise, that COULD be a sign of impending failure. Note that high temperatures will cause it to make more noise. Mine always sounds louder in the Summer. Also note that the CQ fuel pump uses the gasoline to keep it cool. If you run the tank down below 1/4 full, you may hear more of the buzzing bees, either because there's less gas to keep it cool, or the empty tank is amplifying the sound, or a combination of both.
The real sign of impending doom is if your engine is leaning out at high RPMs. This means that the fuel pump cannot provide enough fuel for the engine's high demand. If you suspect a problem with your pump, you should replace the fuel filter first. It's much cheaper and easier (under car in front of left rear wheel).
Pump Replacement (CQ -- sedan will be similar, but less hassle because it's easily accessible):
Symptoms: Smell of gas outside the car after parking, long cranking times to start (fuel pump must repressurize system).
The fuel lines under the car sometimes develop leaks as a result of corrosion at the points where they mount to the body. Replacement lines from Audi are expensive and can be difficult to obtain. For an alternative, flexible copper line has been suggested, but there is a real danger of developing cracks, and it's not DOT legal. The safest bet is to splice in some steel lines rated for high pressure fuel using fuel injection hose to mate with the existing lines.
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