max3.2

Hi,

my 964 C2 is giving me headaches. So some time ago i went for a drive. Car was sitting 2.5 weeks before, jumped to life, no problems. After that, it was garaged for just short of a week (think 6 days).
Went to the car, wanted to start, no way. Completely dead. Not a single light working.
So whats the matter? Did recharge the Batterie to somewhere around 50% / 12.5V idle and went debugging..

First idea: Alternator is going down.
BUT: Last time I was driving it was quite long (two times 1.5h), and just before parking I dropped someone off and restarted the car without any problems. Testing values were: Car off, battery hooked: 12.6VDC, seems ok. Car running: 13.6VDC / 0VAC (that sounds about ok, or???)

Second idea: Idle current
Frunk light unplugged and lets go. With all fuses about 110mA. Radio fuse 5mA, diagnosis fuse (12) 15mA. Rest stays even with all fuses gone.
So thats quite a lot and not really traceable. Ideas? I have MAF mod and dont know what alarm system might be added..
But still: with a , lets say half battery (aroung 50Ah), thats still almost 20 days, something I could live with and I assume is there since I have the car. Never had it sitting longer than 2-3 weeks.

Third: Some high running current the alternator can't cover.
Got a field current meter, and did some testing. Enginge not running, Ignition on: 8.5A. That seems high, but after all its only 100W power - I think is reasonable - someone else have any coparable values at hand?

And fourth: The f**** door switches:
I recall getting annoyed by the interior light last drive and switching it off. When i checked the car today, The passenger door switch was going all but smooth. But it was going...
Is an intermittent failure "reasonable"? Is the current draw high enough (I heard its something with excitation current for power window motors...)? Assuming the half battery (50Ah) and 100mA base draw, additional draw needs to be in the range of roughly 200mA.
Is there any way of getting behinf this?

Any other ideas?

Thanks for reading
Max

DobermanDad

Have you hooked up a multimeter to positive of the battery with the car off and removed each fuse one by one to see what is drawing your power?

max3.2

Well I did choose negative. But that should not really make a difference, if the car aint getting loaded up...
And yes, thats how I determined point 2

Rocket Rob

Your car should draw about 40-60 milliamps with all fuses connected. You have a current drain somewhere. I had a similar problem where my battery kept going flat. I tested my current draw and it was up around 150ma. I isolated mine to fuse #1. The root cause was a faulty CCU. I had swapped it for a known good one and the current draw went down to 50ma. To fix the problem, I had the CCU rebuilt.

Finding current drains is not hard, just a tedious process of elimination. Do you have the electrical diagrams?

tdiquattro

I have completed a couple of changes to reduce ign off and on idle current;
1. modified my door switches to VAG items, miles better.
2. Removed the window regulator relay and fitted a link bypass ie perm on
3. cut off the washer jet heater wires - they are live all the time!
4. removed the glove box light switch and wired into the door switches instead.
5. LED bulbs in the dash/interior lights
6. cleaned and greased all of the earths I could reach
7. removed the brake ware sensors and soldered/heat shrunk the ends
8. converting the frunk catch to 996 with switch and remove old bonnet switch (not yet finished).
9. removed and re-soldered all relays/tracks , rear spoiler controller internals.
10. updated stereo to new
11. rear engine bay fan delete (with bypass mod)
12. rear wiper delete, rear screen demister clean and re-solder tracks in relay, clean connectors.
13. remove/bypass factory alarm and horn
14. re-install current alarm and tracker
15. strip and clean seat adjustment switches
16. remove any unused wires from the internal cabin looms (I have no A/C, no cruise, no sunroof, no rear speaker wires, etc)

I have managed to down size the battery and save a good few kilos out front.

If I were you I would do the window reg, door switches, washer jets, glove box, costs bugggr all and it all helps with reliability.

Cheers

max3.2

I do somewhere. What confuses me is that even with all fuses out I am still running 100mA!

max3.2

Thanks for the tips, sounds like winter list to me

Rocket Rob

If you have a current draw with all fuses removed, I would look for two items. Do you have any aftermarket items installed that are pulling power bypassing the fuse box? And two, you may want to check the diodes in your alternator. They could be leaking and causing a drain.

max3.2

Aftermarket: Not that I know of (on parts bypassing the fuse box)

Diodes: How to check them? Where is the commutator located? Can I remove it to see if current drops? How sophisticated is it? Are we talking 4 Diodes plus big caps or really some solid power regulator ICs...?

Rocket Rob

The diodes are on the back of the alternator. You would need to remove it to see if your current draw stops. If it does, then you would need to have the alternator rebuilt. If disconnecting it doesn't change things then the draw is somewhere else.

One other thought, have you checked the front and rear trunk light switches? They can be one and drain your battery quickly.


See top left of this photo

max3.2

Yes I did check them. Lights are going off. And the lights are in the 10W range, so far above 100mA.

So Alternator is interesting. Right now Im thinking of a way to diagnose the diodes without removing. But that will be hard. Maybe Oscilloscope shows something
Don't have the space and time for a removal at hand.
Have to get new brakes anyway, so they can check

Duck

Any update? I am chasing down the same issue now that I have my rebuild complete and engine back in. I pulled all fuses with no change.