Sir Thomas

2006 A8L 4.2 175k

Never a lick of trbl. always serviced at dealer... Today would not start? Sounds like trying to, but,,, not getting enuf gas?

Have tried jumping in case of dead battery ... Nope.

Still tries to start, just can't catch fully. It then seems to go into a quiet mode for awhile, then later tries to start, but just cant. If it were an older car with a carb, i'd try pumping the accelerator, but pretty sure audi no likey that.

I have an 1999 A8 4.2 250k as back up. Been keeping alive on my own. Have bently manual for 1999, but not 2006.

Sir Thomas

Sir Thomas

purchased obd II reader. no codes, tried twice, no codes

fuel pump?

Shark_V8

The A8 pumps, I don't hear them usually so a sound test would be difficult. Other cars you can hear the pumps spin if you are good.
Therefore test for fuel pressure on the rail. Low rail pressure will cause the start and die condition but the sensor may throw a code idk.

Battery should be a no-brainer. If there is ample grunt to spin the engine and voltage is good, no need to boost. Unless you are cranking forever hoping it will fire. Take it easy on the poor starter motor. 2-3 attempts then let it cool off for a bit.

Good time to put the battery on a charger too, whilst you scratch your head.

MP4.2+6.0

Either fuel pumps or crank sensor as most likelies. Neither may code.

Old school diagnostics (putting aside low value generic code readers): Spray w/ ether (starting fluid) into air intake area. If it starts then dies you can figure it's likely fuel. Can even nurse it along if you have some experience w/ ether but giving it follow on brief shots every few seconds. If it stays dead, no spark so ignition side and then could be crank sensor.

Shark_V8

Does the tach bounce on the A8? That was an old Audi/VW trick is used to verify crank sense function.

I hate ether OMG c'mon here, lets get technical. Can you look at fuel pressure via VCDS?

I can get current to each parking motor :P, current out of battery, ride heights, acceleration#'s, all sorts of data etc etc surely there is a fuel pressure reading in VCDS!

MP4.2+6.0

You're dealing with OBDII crap code scanner said in hard light of day, so no on that--let alone getting into measuring block nuances. Ether is very dependable for me. Diagnosed neighbor's no start Jag XJ8 same way in about 10 minutes having never been under hood before. He told me days later it was what mechanic later confirmed--post tow. Diagnosed no start and then diesel racket sounding snow blower last week over phone where I was suspicious it was nearly out of gas even though they could see some low in tank. Yep...

You also have twin fuel pump set up on ports, and more on FSI's. Sort of Rube Goldberg with the saddle tank transfer function. Lots of folks (and dealers...) have struggled to diagnose those over the years. And with FSI from some posts even dealers seem to be forgetting there is still a pump back at the tank, separate from the underhood HPFP's. In any case, since a good number of posts have confirmed that both fuel pumps and crank sensor can lead to no code situations yet failed parts, may not be able to rely on VCDS diagnostics even if the OP had one. One of the handful of cases where that comes up. And here, we don't now it it is fuel or spark so far--and days of pulling a plug wire are long gone. So I'm returning to remaining simple old school diagnostic I have used successfully in many scenarios. Anyone with a corner hardware store or generic parts place can use same. Just don't inhale or light a match.

Shark_V8

Is there sufficient gas in the tank?

who me? Must have been on Ether...

https://twitter.com/Garage9_com/stat...71287124545536

aTOMic

How long does it crank? If it cranks just a second then stops, seems I recall a part of anti-theft is if the key isn't electronically recognised, this is the result. There's a circular antenna in the ignition switch. Try a different key.
Also, Check yer easy-to-access fuses with a litle yellow fuse tester (NOT a MM). Set aside a day or so, as you probably know A8s have thousands.
Welcome, BTW.

-King Thomas

Shamoye Lewis

if the key isnt recognized it wouldn't even crank..... the fact it cranks the Key Authorize unit recognizes the key....

he can put starting fluid in the intake if it start, no gas or dead pump

ltooz_a6_a8_q7

It was cold, the A8L not used for 2 weeks, when the car doesn't open without the key, I know the battery was low, measured 11.8v. The car cranked tic tic tic than nothing. Charged it for 2 hours at 8A....
http://www.dognmonkey.com/audi/audi-...-right-up.html
Started right up. Got to love A8L

Cheers,
Louis