Battery failure? help!

[PsYcHe]

Could be the earth point behind the driver's wheel..

[David's8]

Originally Posted by PsYcHe

Could be the earth point behind the driver's wheel..

Wished I had taken the pub option Richard! What would other symptoms be if this was the case? (The thing I cant get out of my mind is why did this fault arise whilst the car was not being used? The only thing that changed was the battery loosing charge. Is it related or just coincidence?)
Whatever it is, it now looks like I will need to get the car uplifted and taken to the garage.

[PsYcHe]

I'm sure Mike had a case of this.. running along and then not working.. It's on one of the chassis legs behind the driver's wheel arch liner.

http://forum.a8parts.co.uk/showthrea...ht=earth+point

[brasiliangringo]

You need a conductance tester for the best battery test, not something private people will have. If you are an AA member, call them out and ask them to test it. Simply checking voltage wont tell the whole story

[David's8]

Originally Posted by brasiliangringo

You need a conductance tester for the best battery test, not something private people will have. If you are an AA member, call them out and ask them to test it. Simply checking voltage wont tell the whole story

My current thoughts are that its not the battery - though I may still get it checked by someone with a proper tester. My plan is now (weather permitting) to check the fuel supply (and change the filter which I didnt do at the last service), check the chassis earthing point and then check the coils/ plugs. Can anyone help with how to test the coils?
If, when I have done that,i havent found the issue I may have to get it to the repair shop. My guess is the G163 and G40 camshaft position sensors - tho' how they can fail doing nothing is beyond me. If it is the sensors would VCDS tell me IF I could get the engine started? The earlier scans just showed misfiring with a range of possible causes so how can a faulty sensor be detected?

[Goran]

There are Elsawin procedures for testing all the components. *removed* That was dumb of me, clearly G40 and G163 are different and not swappable. Coil packs you can test by swapping, if one cylinder is misfiring, swap coil packs with a 'good' cylinder and if misfire moves then its likely that coil pack.
I too find it hard to believe its any of these components which all worked when you left the car, still betting its a bad earth or corrosion somewhere supplying low voltage to components. Another random thought, is your ECU box dry inside?

Attached is the Elsawin Hall sender testing procedure. Here is an interesting extract:

Even without a signal from the Hall sensor, the engine will continue to run and can also be re started.

◆ When a fault is detected, the engine control unit produces one spark for each cylinder on every crankshaft revolution.
◆ The fact that the control unit is out of phase by one engine revolution does not have any noticeable effect on the injection system. If this happens, the fuel is injected "upstream" (before the closed inlet valve) instead of while the inlet valve is open. This has only a minor influence on the quality of the air/fuel mixture.

[David's8]

Thanks for that, Goran. I will indeed check the ECU. It has been wet up here and being idle for a month damp/wet is a top candidate for cause of failure (of whatever is the culprit). The swapping of coil packs is probably not going to be a useable method as there are multiple misfires - it sounds like it was running on 3 or 4 out of 8. Besides, it ran sweetly on starting twice before it started mis-firing. (Though now I cant start it at all). The Camshaft Position Sensors should be swappable as they appear to be the same from all the info I have. I gather that they supplement the Crankshaft Position Sensor with regard to timing - hence the comment you found.
Ah well, its stopped raining now so I will go and do some further investigation......

[brasiliangringo]

Im not sure if this has been mentioned as i skimmed read the above, but you should be able to log misfires using measuring blocks in VCDS groups 10-19 under engine channel. Just drive around with the laptop on for a bit etc..

[David's8]

Originally Posted by brasiliangringo

Im not sure if this has been mentioned as i skimmed read the above, but you should be able to log misfires using measuring blocks in VCDS groups 10-19 under engine channel. Just drive around with the laptop on for a bit etc..

Unfortunately I cannot now start the car. I had hoped I could so i could identify the cause of the misfires which came up under the engine controller fault codes. What you have said would, i hoped, give the root cause e.g. CPS G40 sensor or whatever?

[brasiliangringo]

If you cant start it a CPS might be at fault agreed, but they dont often show a code. I had a situation with a 2008 A8 TDI and when hot mainly it wouldnt start and new CPS sorted it - took much head scratching and injector testing etc. Cant recall where they are on the S8 but they are usually easy to replace and not expensive and whilst i hate throwing parts at cars to fix a problem without diagnosing 1st, sometimes its a more economical use of time / money and the only option.