Battery discharging.

Ian Bloxsom · Apr 9, 2008

I know there is an answer to the discharging issue with 964's however I don't seem to be able to find it, on the forum, therefore appologies for asking the question again. Has anyone any idea as to why the battery discharges so quickly. I don't use my car every day however it's usually run twice a week. The car is left, garaged with the alarm and the immobiliser armed. I bought a new battery approx 5 weeks ago and can not keep it charged. I went to use it last night and the battery would not even turn the engine over.[>:] I even have a multimate charger connected, however not all the time. Is there a way of checking the alternator output? Or should I just use the car more often? Thanks.[8|]

Steve Brookes · Apr 9, 2008

Ian, I am in the fortunate position that mine keeps its charge well and I use the car less than you (although my minimum weekly run is a 50 mile round trip I might add). However, I noted that the under bonnet light had been removed before I got the car and the wires taped up to stop them grounding. I've since heard that this is a prime suspect in losing charge so I've not bothered replacing it.

Mark Elder · Apr 9, 2008

Hi Ian,
This is the post you are looking for http://www.porscheclubgbforum.com/tm.asp?m=237726
(Actually the 993 version - but issues are v similar)

kevin · Apr 9, 2008

The quickest and dirtiest way of finding faults, is to pull all teh fuses you think may have circuits that are responsible, and then put an Ameter in circuit, replace fuses one by one until current draw exceeds about 80mA.....IIRC, you have then identified teh circuit and can go from there.

Likely culprits are:-

Door microswitches
Bonnet switch/light
Engine hood switch/light
Green stereo wire
Glovebox microswitch/light.

HTH

Kevin

Ian Bloxsom · Apr 10, 2008

Thanks Guys, this is all good advice. Steve, my hood light is also disconnected, mainly because the switch is broken (I bought the car like that). However the engine cover light is still connected, therefore that's my first port of call tonight. Mark I'll check the 993 link and take it from there. Kevin I,ll also follow your advice and work through the circuits. I appreciate your comments.

Steve Brookes · Apr 10, 2008

I've also heard something about a bad power window relay causing a drain. I think the test is that with the key in the ignition and the door open, you should be able to operate the windows but not if you take the key out. i.e. if the window works with the key out and the door open, the relay is on all the time (and therefore draining). If I've got something wrong about this sequence, can someone else chime in and correct me?

Dave Wilkinson · Apr 10, 2008

Steve,

I'm not convinced. I think the 964 is of an age where there is nothing magical about the key being in the ignition - it's not like a modern car, like a VW, with CANbus which is able to detect the key being taken out of the switch.

I have a feeling there is a difference in the way the windows operate - certainly between US and RoW cars, but perhaps even between MYs too. On my '89 RoW car the windows ALWAYS operate when either door is open, regardless of whether the key is in the ignition or not. With the doors closed the windows only operate when the ignition is switched on.

There have been one or two instances recently where one of the fan relays has fused it's contacts together resulting in the associated fan running permanently until the battery dies. It's the same part number in all cases but there are, potentially, three of them - oil cooler, rear blower and a/c condenser. I would imagine it would be obvious though if one of those was running all the time. The sampler fan behind the CCU is another common culprit where the driver transistor in the CCU blows and provides permanent voltage to the fan.

Regards

Dave

Steve Brookes · Apr 10, 2008

Looks like you're right Dave. Here's the PH post I saw the stuff about the window:

http://www.pistonheads.com/gassing/topic.asp?h=0&t=493679&hw=+%2Bwindow+%2Brelay

Essentially the driver's door window should not operate with key out and door closed but does work when door open, regardless of key. If it works with doors closed and key out then the relay is faulty [&:]

I think we might have some fun with this in the car park on the 11th May [

]

Ian Bloxsom · Apr 11, 2008

Thanks Steve and all you other guys, I'm going to have a fun weekend trying to trace this fault. If anything positive comes out of this I'll let you know.

911addict · Apr 13, 2008

Ian,
More possibles:
- Some of us have had a problem with drain caused by a gremlin to do with the CCU (climate control unit). A small fix was necessary: earthing/mod? But there again the garage may have been giving us BS.
- The battery earth strap also corrodes, and needs replacing.
- recent installation/ messing with hi-fi or alarm?
etc, etc. Good luck.

George Elliott · Apr 19, 2008

I always assumed it was the Alarm system which drains the battery. My 944t was the same.

George

964
944t

Ian Bloxsom · Apr 21, 2008

I've always assumed it was lack of use plus the alarm system. As I haven't had the opportunity to try out all of the suggestions so far, I've resorted to disconnecting the battery (both leads). A bit of a nuisance, however it gets me over the problem short term. I assume there is no harm in disconnecting the battery, if so I feel sure that someone will advise?

iangray100 · Apr 21, 2008

If you have the ccu issue with the little ccu fan running on 24x7 untill the battery dies...in hrs!!..try these options

OPC ...£1000+vat for new one or £650+vat for a OPC exchange unit ..or for a 17p transistor from Maplin get the soldering iron out ;-)

http://forums.rennlist.com/rennforums/showthread.php?t=276844&highlight=bc337

http://forums.rennlist.com/rennforums/showthread.php?t=359909&highlight=bc337

Ian Bloxsom · Apr 22, 2008

Ian,
thanks for this. The CCU fan does run on after the iginition is switched off, however not 24 - 7. It's usually for about 10 to 15 minutes, but I've been told this is normal. I'll now look at the options you recommend.

kevin · Apr 22, 2008

ORIGINAL: Ian Bloxsom

Ian,
thanks for this. The CCU fan does run on after the iginition is switched off, however not 24 - 7. It's usually for about 10 to 15 minutes, but I've been told this is normal. I'll now look at the options you recommend.

Perfectly normal, and all to do IIRC with engine over temp sensing..

Kevin

peanut · Apr 22, 2008

ORIGINAL: kevin

The quickest and dirtiest way of finding faults, is to pull all teh fuses you think may have circuits that are responsible, and then put an Ameter in circuit, replace fuses one by one until current draw exceeds about 80mA.....IIRC, you have then identified teh circuit and can go from there.

Likely culprits are:-

Door microswitches
Bonnet switch/light
Engine hood switch/light
Green stereo wire
Glovebox microswitch/light.

HTH

Kevin

good solution Kevin. This is definitly the easiesy way to go if you are DIY.

Another way of doing this if you do not have access to a multimeter is to remove all the fuses . Remove the earth lead then touch the earth strap connector lightly onto the battery terminal. You should have zero arcing .

Then replace the fuses one by one testing each time by touching the battery connector onto the terminal. If you get a very slight arching then the fuse you have last replaced is the culpret circuit. The slight arching is caused by current being drawn from the battery into a circuit that should be switched off .
Observe the usual precautions when working near a battery and ensure plenty of ventilation.

GMcMillan · Apr 23, 2008

Hi,probably not a great idea to disconnect & reconnect a battery terminal to check for arcing as Bosch ecu's don't always like this,use a cheap ammeter instead. Heater fans are allowed to keep running for 15 min, this is normal. Windows from 3.2s on should work with door open & key out,this is so you don't have to refit the key if you have forgotton to close a window. If you still havnt got to bottom of current drain let me know. Don't forget to check charging rate.

iangray100 · Apr 25, 2008

It would be far better to get yourself a cheap clamp Amp meter ..available at Maplin £9.99 etc etc then you don't have to disconnect anything.

http://www.maplin.co.uk/module.aspx?ModuleNo=46931&doy=25m4

I have recently been diagnosing my new increased battery drain and found the climate control unit (CCU) fan was on 24x7. £800 for a recon unit from OPC!! or fixed with a 17p transistor on the control board...;-) ....great result!!

GMcMillan · Apr 26, 2008

Good idea of an amp clamp but I have yet to see one that is very accurate especially as we are looking for such a small drain.

peanut · Apr 26, 2008

ORIGINAL: iangray100

It would be far better to get yourself a cheap clamp Amp meter ..available at Maplin £9.99 etc etc then you don't have to disconnect anything.

http://www.maplin.co.uk/module.aspx?ModuleNo=46931&doy=25m4

I have recently been diagnosing my new increased battery drain and found the climate control unit (CCU) fan was on 24x7. £800 for a recon unit from OPC!! or fixed with a 17p transistor on the control board...;-) ....great result!!

Nice result Ian thanks for posting it . I'm sure its one of the last suspects most of us would expect. It just shows you you cannot rule out anything.