My A8L questions

[amvauto1]

So my questions are for my 2001 A8L, 1. have a gas smell when i open my sunroof, now 1 of my cats is malfunctioned, but weird, not all the time but at least half the time the smell is strong, could it be from the cat itself? 2. how long ure pads and rotors last, my rear pad is done and only have for 2 yrs or so as well as rotor.

[silverd2]

1.Gas smell not likely to have anything to do with cats.
What codes have you read?
How many miles on the car?

2. Depends on yearly mileage and your type driving. I've gotten about 35-40 miles out of front and rear pads...and double that out of rotors...2 sets of pads before rotors reach thickness wear limit...that's always been the case with every German car I've had (have).

[Kneale Brownson]

If your rear pads wear faster than your fronts, you have sticky parking brake issues.

[amvauto1]

Havent done a scan just yet, has approx 150k (miles) runs great, just damn smell, last scan I did I remember, things related to Cat, O2 Sensor and some misfires, etc...

[silverd2]

Originally Posted by amvauto1

Havent done a scan just yet, has approx 150k (miles) runs great, just damn smell, last scan I did I remember, things related to Cat, O2 Sensor and some misfires, etc...

Failed front 02 sensors can make a engine burn a little rich (maybe "sweet" exhaust smell), but shouldn't produce a raw gas smell, though.
If they are the originals, they need to be changed...will smooth the engine and usually improve mpg's a little. 100K is about the limit on those.

[pocketchange]

If you are smelling raw gas, I'd suggest you forego driving until you rectify the problem.

The fuel system on the A8 is not that complicated. Start from (you pic-it) one end checking as you go for leaks. A good place to look first is for loose fitting on or near the fuel rail under the dress covers/trim over the engine. If you don't find it there, go to the "boot" and check the pump fitting, filter, filler pipe, etc..
pc

[A8Fixer]

My first post...

I'll second what "pocketchange" said above. Raw gas smell manifested itself when I opened the sunroof as well (with a full gas tank). The problem was in the trunk. The locking ring for the fuel level sender (driver's side under carpet near back seat) was loose and resulted in gas leaking into the trunk. I also had a P0455 CEL (large EVAP leak) because the tank wouldn't hold vacuum. A loose gas cap can give you the same error.

[silverd2]

Originally Posted by A8Fixer

My first post...

I'll second what "pocketchange" said above. Raw gas smell manifested itself when I opened the sunroof as well (with a full gas tank). The problem was in the trunk. The locking ring for the fuel level sender (driver's side under carpet near back seat) was loose and resulted in gas leaking into the trunk. I also had a P0455 CEL (large EVAP leak) because the tank wouldn't hold vacuum. A loose gas cap can give you the same error.

Good place to look, but the "leak" codes come from a tank (or anywhere in evap) that won't hold pressure. Great pains are taken to see to it that tanks can't hold vacuum...gas cap has one way vent that opens inward only, to prevent vacuum from forming.

The leak detection pump (up in left rear fender well) pressurizes the air space in the tank (and entire evap system) every time you start the car, then times any bleed down of vapor pressure, to detect any evap (tank vapor) leaks...quick bleed down=large leak...medium speed bleed down of pressure=small leak. VERY slow or no bleed down=system OK.