D3 A8 Fuel Filter Service Notes (2006 W12)
 

This one was pretty easy. Again, vehicle is approaching 95,000 miles and now 7+ years old so I want to roll through some of the rarely serviced items. I try to do fuel filters once or twice in the life of the vehicle. If it saves me a fuel pump(s) change, that's a bunch of diagnostics, hassle and $ for the posters who have been through it. I haven't lost a fuel pump since one very early CIS injected C1, and only one of my hand me down old Audis (a C3) needed a pump late on. W12's can flow a lot of fuel too, so all the more reason.

Fuel filter is tucked underneath below the right rear passenger (U.S. vehicle) door. At least on mine, there is an aero plastic panel that completely conceals it. As with my differential service, I still had the car on the ramps so proceeded to do this. A bunch of 10mm fasteners and a few snap clips hold it. All reusable if careful; just took a nut driver and small screwdriver to free the snap clips.

Once I got the panel off, the filter was right there. See second picture. Mine has the type with two openings on one side, and one on the outlet side. On the side with two, turns out the smaller diameter one near the edge is the apparent true inlet and is stamped "IN." I'm guessing the other one is some kind of smog/vapor port thing. Apparently in the relatively late W12's, the filter was changed to one with only one port on each side. Hard to track down the exact configurations here; either order by VIN or get under that cover to see what you really have. Other motors may well vary at part number level too.

FWIW, filter I pulled is the original almost certainly, with a manufacture date almost a year before the car was built. A "UFI" brand (never heard of that; made in Italy) with OE part numbers on it (obsolete, 4F0 201 511B). Replacement filter (see picture) was ordered by VIN as 4E0 201 511A, fit perfectly and looks virtually identical. I also first bought a Mann filter off of Amazon using a part # cross reference to WK720/3. Looks the same, same 3 ports, same one marked "IN." Same "4.0 Bar" pressure noted on it as on the one I pulled. But candidly, the "Made in China" marking didn't grab me, all the more since it's A6's from China, not A8's AFAIK, and the construction seemed a bit different at the ends than either the old or new Audi branded ones. So I ultimately passed on that Mann one. Usually I find Mann is identical and usually made in Germany, so this surprised me, especially for a pretty recent A8 with an unusual motor.

Lines came off pretty easily. First I opened the plastic filter retaining clamp up. Obvious in the picture below. A tri square type fastener, near 8mm in apparent size. No trouble with it stripping, not turning or anything as someone in a recent post noted. Actually it was almost loose to the touch when I first turned it. I squeezed the plastic pressure fit fuel line attachments lightly with a pair of pliers (at the points on the fittings sticking out a bit) as I tried to pull loose by hand. Pretty intuitive. I didn't want to break anything. They yielded fairly easily. As usual, I got the initial spray of pressurized gas as I cracked the first one. I try to always do these outside and well away from gas water heaters and such as a result. Also as usual, by the time I pulled all the lines, the filter was draining its gas no matter how fast I got the drain pan near.

Bolted filter back in. Then I started car before fitting cover to be sure no leaks at the connectors or otherwise. Fired up in 5 to 10 seconds and ran smoothly within first second or two. No leaks as expected, so I refit cover. Took a while to sort out the plastic washers associated with the 10mm plastic nuts, but it all made sense after a while (probably should have laid them out in order as I removed them, but I didn't realize there was an upper washer component that sometimes separated and sometimes didn't).

Observations/did I need to: as usual, I drained filter fully when done. Then I blew through it, from both inlet and outlet sides. Frankly, back pressure was pretty minimal; relatively clean apparently. One or two other D3 posts though that I recall have indicated a lot of back pressure/likely dirty, so my findings are better. I owned car from 15K miles and other than a handful of odd/no choice gas stations EVER, it always gets Tier 1 gas at typically high volume stations. Again, having done it on my C5 4.2 already, that A6 seemed more clogged with about 25% more miles, but also with better MPG's and less displacement (i.e. less fuel flow). Net, I could have skipped it at this point, but other data points suggest it is variable. If I reduce the risk of breakdown and diagnostics on multiple fuel pump set up--those posts often seemed prolonged and frustrating to the owner, even ones w/ a lot of experience--I'm happy.

I’ve done the same on my A8 2007 4.2 FSI last year when it had 54 K Km (33.5 K Miles). The filter is relatively inexpensive and it has pressure regulator inside. The process to replace it took about 15 min or so. Based on those reasons I decided replace it each 55 K Km (34 K Miles).

But what is interesting, my original filter was from MANN made in China. The new one is also MANN and also made in China. :)
I’ve done 10 K on it already, but it sounds like some of the original parts are made in China already.

It is not always 15 minutes job. If that single bolt goes rusty you have to cut it. Not easy underneath the car.

I’m sure it depends from the year of the car. In my case 2007 D3 it is a plastic holder and metal bolt. So, I cannot imagine the situation when you need to cut it. Even if it will be much rusted it should easy go out of there. At least in my case it was not rusted and I didn’t apply any force. It was very easy to pull it off. Also, I didn’t apply too much force when I put it back.
So, overall I think it is easy easy, unlike I had experience changing rear brakes ( see my post with description of the issue... still no one pointed where I was wrong and why it happened such way in my case. Nor anyone indicated exact steps they used to do to get it replaced)

Misha R!
BTW. I have exactly the same plastic holder as you can see on the pictures posted by MP. So, you'll be able to pull the filter always and always EASY!

Don't be too optimistic. I have just the same holder and the bolt, BUT, there is a metal nut inside that plastic and when it get stacked to the bolt (easily over time and some salty water) it will start turning inside that plastic and there is no way to get to it. In that case jigsaw is your only friend. Greasing that bolt would probably help to prevent rusting and that is actually point of this post. :)

Aha! I was not aware of that!!!!
I thought it just a plastic inside.
I'll grease it next time :)

Or...
 

anti seize compound for best of both. FWIW, mine was really easy; as I said almost was loose in terms of pressure. But then I'm an almost no salt and winter road crud coastal owner (except on Tahoe trips) in a Mediterranean climate zone.

Mishar is totally correct on this one. I just tried changing my fuel filter only to be utterly disappointed to find my bolt rusted and seized to the rear metal piece. I don't have any way off cutting the bolt so I had to give up on the task. Waste of my Sunday morning. Now I have to take to mechanic and have them mess with it. Such a terrible design.

You can cut it with hand saw blade. Not easy but works. Another way is to cut that plastic and use strap ties to fix new filter back.