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Tech Article

Audi C5 A6 Quattro 4.2 V8 How to Remove and Replace the Fuel Pump

Last Updated: 09/24/2017
Parts Group: Fuel pump
This article discusses the components involved with removing and replacing the fuel pump for the C5 Audi A6 Quattro 4.2 V8 as made from 1999 to 2004. This article is based on a project that we did today.

It's a fairly complicated set up, so I am giving a high-level overview of the main components involved.

For replacing the fuel pump, the relevant components were all located under the rear passenger seat squab. It was easy to lift this up and reach underneath to disconnect two large electrical connectors. There was also a smaller purple-and-yellow connector that I suspect to be part of the airbag system. It was already disconnected.

With the seat squab removed, the next component was visible: a black metal cover screwed tightly against to the body of the car, under the seat squab, with sheet metal screws. If the cover has been installed the correct way around, then the slight protrusion atop the cover is biased towards the front. With the cover off, we could see a round hole in the body of the car, perhaps 6” in diameter. Underneath that were more components relevant to the fuel pump.

The next part we removed was a yellowish metal ring. This ring is intended to rotate so as to wedge the fuel pump contraption down tightly against the fuel tank. We found that a good way to loosen this ring is to rotate it by tapping it with a hammer, using a screwdriver to transmit the shock and focus the impact. Once this ring was removed, the underlying components were essenitally loose and could be moved around, even lifted out.

The next component to remove was the sturdy plastic cover right above the fuel pump. This seals the round hole in the top of the fuel tank. The hole is perhaps 5” in diameter. The cover is basically a sort of clearing-house for fuel flow and electrical current flow. Atop the cover were attachment points for two black fuel hoses, each held tight with a clamp. One fuel hose carries the high-pressure fuel from the fuel pump into the fuel rail, whereas the other hose accepts fuel flowing back from the fuel rail, through the pressure regulator, into the tank. Below the cover we found the two corresponding brown inside-the-tank fuel hoses. One of these led to a plastic (and fragile) nipple at the top center of the fuel pump. The other led to the depths of the fuel tank somewhere.

We proved that it’s to get confused as to which is which, so a good practice is to detach the fuel hose from the top of the departing fuel pump and then immediately attach it to the top of the replacement fuel pump. It’s also a good idea to keep the cover as close as reasonably possible to its original location and position, so as to prevent a situation where we’re wondering how to get all the hoses and wires stuffed just-so back into the fuel tank and atop the fuel pump, while they’re attached to the bottom of the cover.

We figure that of the two black rubber hoses leading to and from the fuel tank, the passenger side hose is the the one that carries the fuel away from the fuel pump toward the fuel rail. We conclude this because attached to it, underneath, is a length of brown inside-the-tank hose that goes to the fuel pump. More blatantly, arrows embossed on the plastic atop the cover also show the direction of flow.

At the bottom of the cover are two electrical-connector plugs, one of them brown and the other one black. If these don’t get removed, as part of replacing the fuel pump, better yet. Attached to the bottom of the cover are also two loose electrical wires, one of them yellow and the other one black. At the other end, each of these wires has a spade connector at its end. These two spade connectors fitted into two male connectors atop the fuel pump. The connectors are different sizes. This made it impossible to connect them the wrong way around. The connectors atop the fuel pump could be separated by gentle pulling.

Below the place that the plastic cover vacated is a large rubber seal, presumably to contain gasoline vapors to the inside of the tank. This seal can be lifted up and away. I gather it’s typically prudent to replace this with a new part when swapping out the fuel pump.

Inside the hole in the fuel tank is visible a white plastic basket-like structure that essentially locates the fuel pump right at its center, with the pump mounted vertically with its electrical connections at the top. The pump can simply be lifted up and out of the hole. It’s a lot more pleasant to do this when there’s not a lot of fuel in the tank. Integral to the bottom of the fuel pump is a filtration screen through which fuel is sucked into the pump.

Below the fuel pump is a sort of cave or indentation in the plastic part of the fuel tank, shaped to cozily hold the fuel pump basket in position.
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