Engine issues 11 codes
 

Long story cut short, the A8's Aux pulley failed.

The AA recovered the car back the last few miles to my place on battery power alone (over the tow limit for his van, and no trucks available).

Apparently, the car conked out again, he installed a new battery and continued the journey. It conked out again around 500 yards from my house.

I then had to recover the AA guy as he couldn't get the car started, and was parked on a blind bend.

He said the car just started to splutter and die, like it was suffering fuel starvation.

So I charged the battery up, and threw the code reader on it.

Codes

17521 Lambda B1S1 (knew this had failed and needed replacing)
16814 Catalyst System B2 Low Signal
16711 Knock sensor low signal
16946 System voltage low
17536 Fuel trim B1 lean
17538 Fuel trim B2 lean
16684 Cylinder misfire - unknown
16685 Cyl 1 misfire
16686 Cyl 2 misfire
18010 Power supply B+ terminal 30 voltage low

Now a few of those are due to low voltage (going to clear the codes and recrank and see if they come back with a fresh battery).

The aux belt tensioner still needs installation. However, I would have thought the car would run for a short while without the alt-charging.

It's the issue with the misfires that are bothering me. Something seems to have gone wrong on the recovery drive.

Is there any quirk with the A8 that may have contributed to these issues? maybe some insight that will help me focus on a particular area to get things running again.

Regards

James

Could very well be fuel pump gone. Have seen it happen couple of times when battery goes low. Voltage goes down, amps have to go up to keep power up, too much amps for too long and it burns out.

I reckon you get the tensioner sorted out first. Whilst waiting on that, put the battery on a trickle charge so it has a full charge when ready. Then with the battery installed, have it on the trickle charger, scan the car, saved the codes, clear the codes, start it and take for a drive. Scan it again when you get back to see what resurfaces.

They may be old, but there is still a lot of electrics to drain the battery. Fingers crossed that it's only due to a low battery that you have the misfires, maybe due to fuel pumps not running at full power.

I'm with Ainars on this one. I had it happen to me. Alternator failed and I almost completed the journey on battery alone. As the voltage drops the fuel pump draws more amps and eventually will fail. Mine actually failed on my drive as I arrived home! Had to tow the car to it's parking slot with the quad!

Thanks all for the suggestions on where to start looking. It does seem similar to the time when the pump failed a few years ago.

Can anyone jog my memory ... If I disconnect the fuel line is there a few terminals I can bridge to run the pump or will cranking suffice?

Annoyingly I did the pump not that long ago, so that will be frustrating if the AA man killed it by driving it back on battery power alone.

Honestly, for the distance he drove it, I could have just towed it home with a tow rope and saved the problems this has caused.

The A8 is my dad's car, and I have been keeping it on the road for the past few years. At this point, he just wants to chuck in the towel and send it for scrap!

Criminal waste of a good car!

I need to decide what to do, as he doesn't want to spend anything more on it.

You can run 12v straight to the pump to see if it's working. Cranking only runs the pump for a few seconds until the engine starts.
HtH

I use this when I want to run the fuel pump. It's literally an old fuel pump relay with the plastic cap removed. Push down on the top with your finger and the fuel pump runs. If its working of course.