SS_RTR

I have recently purchased a 2007 A8. I got a CEL yesterday while driving. Later at home I had started the car and was loading a CD in the changer when the car stalled. It then would not start, but it would turn over. A few minutes later it started. This morning, it did not start, but after trying again 2-3 minutes later it started and I was able to drive it 10-20 miles with no issues. Since, I have yet to get it to start.

The place I purchased the car from had said they had to replace a fuel pressure switch. They said if I can get the car back to them, they will pull the codes and get it fixed. They think it's still fuel related. I was leaning towards a bad crankshaft position sensor. I don't have VCDS/hex-usb+can cable yet, just ordered the all out upgrade today from RossTech. I do have VCDS-lite and a dumb cable that I used with my 2003 A4 but it won't work on the A8.

Is there any way, without pulling codes, I could determine if this a bad fuel pump or a bad crankshaft position sensor? I'm afraid I'm not going to get this to crank again as is.

mishar

Welcome!

As you already know about VCDS no need to explain anything. If I have to guess I would say crankshaft sensor. It can come and go while dying. There are two pumps and engine will start with only one. Besides that when pump is dead it won't come back.

Mister Bally

Use VCDS to confirm. Likely the crankshaft sensor. Usual failure mode is no restart when sensor (engine) is hot. Will work ok when cool.

Happened to me. I posted a thread about it two or three years ago. Interesting story. It involved Mrs. Bally & I walking home a long way in the Summer heat. She had flip-flops and was not happy about the blisters. Search for the thread, it's out here

SS_RTR

I have the tire and shroud out. Do I need to going at this from underneath and remove plastic pans underneath or continue from the wheel well. I can't seem to get the orientation on where this sensor is. I've seen some other 2003 and 2004 posts but not sure if those are the same. I was going to try and clean the sender and check for burnt wires. Car hasn't cranked since my last post and I've had to charge the battery. To complicate things, battery was too low for MMI to start so that I could set the car to lift/jack mode.

Mister Bally

You need the service manual to be certain of the procedure. On my '04;the bottom panels under the engine and transmission had to be removed as well as the heat shield around the inboard CV joint which requires wheel and wheel well cover removal. Long extensions, universal joints as well as inner "star" sockets.

SS_RTR

For service manual, are you referring to the Bently Audi A8, A8L, S8 2004, 2005, 2006, 2007, 2008, 2009 Repair Manual on DVD with ISBN: 978-0837612591

Mister Bally

That one or the Elsa manual.

SS_RTR

I wanted to give an update on this. Since I had just bought the car used, the dealer agreed to the starting issue. Root cause was a combination of a fuel pump relay and the high pressure fuel pump. Since those were items were replaced, I've not had any problems starting issues.