Cain74

I have found a 2005 A8 W12 in good shape, so says the salesman, with the only problem being that the check engine light has come on with a code of a misfire. They replaced the coil packs and still had a problem. after more investigation they found that cylinder #2 has low compression (75), but the others are good. To me it sounds like it is either worn rings or a bad valve, possibly a head gasket issue. Either way it sounds expensive. Any thoughts on how much it might cost? Has this been a known issue with this engine? The salesman says that you don't even feel that the car misfires, but I never trust them.

03_AR_CO

I am no expert here, but I would guarantee that a compression issue on the W12 engine would be costly, easily into the 1000's. I am not telling you what to do by any means, if you are looking for a project car, this might be a great opportunity, if not, I would run for the hills. Just my two cents, and see what others here have to say.

Bangerla

You may want to check on VW vortex forum for the VW Phaeton, since the W12 was available in the VW earlier in the states. They will have higher mileage, and may have run into this. The dealer should also check to see if the compression is low when hot as well as cold.

mishar

That is very low compression. That cylinder doesn't work at all on idle. May be catching up on higher rpm. It can be fixed but that would be expensive. Cheaper if it is valve and more expensive if it is rings. Very expensive if it is a piston because it can be a block too. I wouldn't go for it if it is not $15K less than the good one.

tx170754

Had a Phaeton for 2 1/2 years and have been on the Phaeton forum, never heard something like this, the W12 engines are very reliable, I would not buy the car.

TSHong

I agree with the other posters already, it would be a costly repair. Even if you can't feel it, the engine would not pass an emissions test if your local law requires one.

mishar

It probably would if he unplug that injector. Not a Vancouver AirCare. Not with the engine light on.

There is a trick to figure out if it is a valve or rings. First measure it as is, than pore some oil into the cylinder (10 g or 1/3 ounce) and measure again. If there is significant jump in compression it is rings. If not it is valve.

MP4.2+6.0

Pass on it w/ out further info.

Block or piston/ring problem would be a nightmare; head more straightforward. More likely the head (valve or maybe gasket leak), but without further diagnostics per other posts or also finding that it is burning oil [thus trending toward a ring issue], not enough info to tell.

Motor is big bucks, but even pulling motor is very time consuming. Head could likely be done with rest of motor in the car, but most likely not the pistons/rings--at least by most shops. I have done a few internal motor jobs with a block in the car; but nothing on newer Audis; I doubt many shops want to do something like that.

Having been on the board 6 years with mine, having read the board back to p. 1, and also following other boards like QW, there is essentially zero history of serious internal motor issues with the W12 that have been posted. They may exist, but they haven't come out here. Thus, you're dealing with an unusual scenario.

Cain74

Thanks for all the replies. I don't think I'll get the car, though I do come from the school of learn things the hard way. Part of me wants to believe that it's just the valves and the cost won't be as bad as if it were the rings, but my luck it would be the rings. Any idea what would have caused just one cylinder to go bad? Would valve work cost between 2-3k or more?

addautocycle

i would say more than 2-3k. did you ever say how many miles on it?