Won't start - 2nd time this week
 

Monday morning my 2002 S8 was flat as a pancake and had to be jump started off my wife's mini (oh, the shame!:o). I assumed that, as I'd cleaned it inside and out on the Sunday, that I'd switched something on accidentally and the battery had drained whilst it was left standing on the drive.

It was fine all week. Five 35 mile each way commutes in the dark and the odd trip to the shop at lunchtime.

But tonight, came home, went out an hour later to pick up my daughter, waited outside her place of work for 10 minutes with side lights and the TV on and....flat as a pancake again.

Doesn't really sound like a battery or alternator fault - but I might be wrong...

...any ideas on where to start guys?

Volt meter across the battery terminals when the car is running should give about 14V. If it doesn't then Alternator problems???? or bad earth . My thread here may help.

As Mike says above..

But given the age of the car, it could just be that the battery is going and with the extra load on the dark mornings/nights it's just not getting itself sorted anymore.

Well I only drove about half a mile after the jump start last night, left the car outside overnight and it started this morning! A bit sluggish, but there you go.

The voltmeter shows 13.8 volts across the battery with the engine running...so where are these pesky earths?

Drivers side wheel arch, on the chassis rail you will see a wee black box that has the cable from the battery going in and the lead to the starter motor and alternator going out. Next to it is the earth lead from the engine to the chassis.

Front or back? I've got the front driver's side wheel off and can't see a black box....

It must be hard to find as - following earlier thread - I asked my garage to check it before last winter. They couldn't find it and so didn't do it, but did clear scuttle drains etc.

Found a black box above the battery in the boot, but everything is like new in there.. Put a 10mm socket on and tightened each connection up - but I suspect that's not what I'm looking for is it?

BTW - the battery has 12.25 volts across it - is that OK?

Still, off-side front wheel is now very clean!

http://i25.photobucket.com/albums/c7...37-resized.jpg

This photo shows the brown earth wire left of the socket ratchet. The purple connector is next to the battery connection box.

The schematic

http://forum.a8parts.co.uk/attachmen...1&d=1288441791

Silly Q... But was this maybe moved on the FL model?

The schematic is from a 2002 S8.

Found it! Just off to remove and clean - thanks!

Presumably it's just the earth taht needs cleaning up?

Well, that was pretty corroded! Blue-coloured crud all over the place. Now cleaned, vaselined and WD40'd (the earth connection as well!). Started a treat after that...just hope it carries on doing so.

THANKS LOADS for you help guys - don't know what I'd do without you. Beers on me for the March meet.

Dismantled first?

I took the earth cable off before I cleaned it - is that what you mean?

+++

Great results there. Don't suppose you have any pics of what it looked like before or after cleaning? ... always useful for a sticky and the rest of us if we ever face it. :)

Oli

No pics I'm afraid - still not got used to having a camera on my phone!

But it was VERY crusty with that blue coloured muck that electrical terminals seem to foster. Had to get a file to the flat on the chassis and to the washer, as just sand paper wasn't going to shift it.

Next time you have the front o/s wheel off, it's probably worth having a look. It's just where 'the librarian' says, you can unclip whatever the purlple wire goes into then, for easy access, I removed the battery/starter motor cable junction box with just a couple of Allen keys and voila - there's the earth.

Forgot to say - in the picture from 'the librarian', the wheel arch liners are removed. You don't have to do this as there's a small 'panel' about 6-8" square (but it's not square - it's shaped) that you can easily remove - just one plastic nut and a circular clip to get access. You can identify the panel easily as it has some Audi numbering on it moulded into the plastic.

Didn't start this afternoon again FFS! Battery down well below 12 volts before I tried, so suspect that it's useless now. Off to halfrauds for a new battery tomorrow.

you said it was at 12.25v......thats low anyway................from what i read on wikipedia batteries are 12.6ish at rest (check out automotive batteries on wikipedia) at 12.25 you got 50%ish power in it. Not good for a V8 in winter :D

You probably had a dying battery and the crud was making it harder for it to do its job too.........

Tis the time of year for roiuting out the weak batteries. For future reference, when a low battery starts causing starting issues I have found the following checks useful;

Note values are from memory so could be +/- 0.5 volt.

1. As mentioned before check the voltage at the battery with the engine running, should be about 14 volts. Anything test 2 result to 13.5 volts suspect wiring/earths (see tests 3 and 4).

2. With the engine off check the battery voltage under load. This means switch on head lights, main beam, heated screens, heated seats. The voltage will drop but should hold around 11-12 voltsish. If the voltage continues drop and goes south of 9.5 volts, chances are your battery is dead. Take it to a motor factors and they should be able to test it properly for you with a proper load probe. Before doing this check be prepared to not be able to start the car after, so be somewhere you can jump start.

3. Measure the voltage between the -ve battery terminal and chassis and -ve battery terminal and engine block. Should be less than 0.1 volts. Anything more start looking at battery terminal connections and earth points as described above.

4. Measure voltage between +ve battery terminal and alternator +ve, and +ve battery terminal and +ve in main fusebox. Should be less than 0.1 volts again, wiring and connections likely causes of any high readings.

As I say all from memory so happy to take a hit on the exact values. When I get chance I'll do the readings and update, unless anyone with a good battery beats me to it.

Another import thing to remember with starting issues is just because you have a new or recent battery do not rule out it could still be duff. Have seen this many times.

Much appreciated guys. Off for a test and, probably a new battery, at lunchtime