Alright,

the latest issue is this: something on my car is killing my battery's charge when the car is off. First off, I have two fairly new batteries (one 6 months old, and the other 2 months old) - the batteries have both been checked and are fine. Furthermore, my Porsche authorized specialist has checked the charging system and finds it to be in perfect working order. Any ideas as to what might be causing this drain? To give you an idea, the car will run fine and start throughout the day, but if it sits for 10 hours or more, it will need a jump. The only thing that is of note recently... my convertible top began working intermittently, mostly not working really (i think a bad switch in the dash- am I right??!) - any connection to the drain perhaps?? I wasn't too worried about the top since its winter now and was taking my time addressing that. These electircal problems can drive a guy crazy, so any help or suggestion would be appreciated. Thanks,

Ken.

 

The only such issue I've experienced involved the door-activated light switches located beneath the upper hinge in the forward door jam. In a coupe, and probably targa, it's easy to determine if you have a faulty switch--the interior lights will not switch on when you open the door. I don't recall the type of lights found in a cab, though.

There's a relationship between these door switches and other powered systems. Normally, when you exit your car, the interior lights stay on for some 30 seconds and then shut off. With bad switches, the shut down sequence doesn't occur and the powered windows remain functional (you need to remain seated, remove the key and open and close the door to test this).

After replacing these switches, the lights/windows shut off properly and my battery now holds a charge for weeks so I believe that was the cause of my power drain. Here are other possible causes and cures from the Porsche 964 Titanic site.
Good luck!

 

Dear Ken,
I am assuming you are using the correct capacity battery? 88 amp hour for a cab.
10 hours to require a jump is a fairly substantial drain. You need to find it. This is not a difficult job. You disconnect the negative lead from the battery, you connect a multimeter in series with the disconnected cable and the battery terminal, set to read amps and use the 10 amp range. You see what the current drain is, circa 2 amps I would imagine and then you start at fuse No 1 and start pulling them out one by one and waiting to see the when the current load drops.
Until you have doen some basic troubleshooting you will achieve nothing I am afraid.
There is a large section in my book on all of this with instructions of how and what to look for.
Ciao,
Adrian
964C4

 

When one thinks there's a current drain on the battery, one needs to check
it with an ampmeter set to milliamps (Check 1st for high drain at amps setting.).
The MAX draw on ANY car should be less than 100ma and typically less than
50ma.

The common problem that I see on 964s is the climate control unit not turning
off the suction fan behind the CCU. Also, if this is the problem, fan in the engine
compartment may also not turn off.

In any case, begin by checking for the actual draw values. Please, no use
of testlights when checking for a small draw. Check out this website
(www.systemsc.com) on the Problems page. It may provide some additional
info.

Have Fun
Loren
'88 3.2

 

Thanks Joey my battery drain problem sound just like yours and I know that my door switch is not always working b/c the lights do not always come on when I open the door.

 

Guys,
I will just offer this little bit of advice when looking for a current drain. You need three things for a current drain.
12V DC
Earth
Resistive circuit between 12V and earth.
A short circuit will blow a fuse.
An earth switching switch cannot cause a current drain unless it applies an earth to a circuit thereis something in between and 12V at the other end and they are all connected.
No light no circuit no current drain to use the interior light as an example.

The most common current drains are the luggage compartment and engine lid lights.

The 10 hours has also to be taken into consideration. A rear blower fan running kills the battery in short order.
10 hours is a current drain of circa 4 to 8 amps. That is not a standard current drain that is something seriously running without stopping. An engine compartment light is around 0.2 amps total of 1 amp between them all.
Ciao,
Adrian
964C4

PS: Flat battery in 10 hours, make sure you have the mulitmeter set to 10 amps range otherwise you are going to fry it.

 

964 Kid- check that blasted Climate Control Unit as well! That was my problem- was able to temporarily stop the drain by simply pulling out the fuse (I believe fuse #1, but check the fuse box cover), until getting a new unit.

Andrew

 

Thanks a lot guys, I'm gonna first try Adrian's approach, and hopefullt get to the bottom of all this. One note: to Joey, the door switch on the drivers side is definitely suspect (the interior light only come on when opening the passenger door, so I think the windows etc are stayng on after I leave). But the car has done this for 2 years, and never caused the car to fail to start - but might be a contributing factor. I'll get to the bottom of this this evening - thanks again!

 

Good luck. Hope it's easy as the switches but failing that, you've got some pretty good advice, here, to take you through the next steps.

 

Well, after some quick tests, the switch in the drivers side is definitely not working. Do you know the part number/cost? Thanks... I'm thinking there may be something else happening also, gotta take some more time and see what it might be.

 

I just dropped mine off at the dealer this morning for the same problem. I will let you know what it is.

Rob

 

Interior light not coming on when door is opened could be just poor ground on the switch in the doorframe. I unscrewed mine and cleaned the earth contact surface (based on advisce on this forum), and my interior light is working perfect again.

 

Try to focus on the problem, i.e. It appears as if there's an excessive
draw draining the battery sooner than expected". Given this problem,
now measure the draw to determine if the source of the battery problem
is an excessive draw. The draw should be less than 50 to 70 ma for
a good start in about 10 days.

Guessing at possible problems is not a good troubleshooting technique!

Good Luck
Loren
'88 3.2

 

hallo
I have seen a few Times that the suction Fan on the AC-Control unit is the Problem . You have a 1990 car ( no Airbag ) just look under the Dash to see the backside of the Ac unit . On the left side is a round device about 2 inches in Diameter with a Hose connected ( goes to the Vent in the Front of the Unit ). it has a opening on the side .
CAREFULLY hold a finger into the opening if you feel now a rush to your Finger the Fan is on . Just unplug it on the Acunit ( white plugin with 2 cables blue and white ) .
You can also hear that Fan , by holding your ear to the Dash , but it is very quiet .
harald

 

My problem posted in another thread was a dead battery after one week. After testing I found that I have about 44 mamp draw which doesn't seem too high. My battery is 700 CCA. Maybe that's not adequate for the winter? After some tests with the voltmeter, the battery looks good and the charging system appears to be fine. I'm just waiting to see if it happens again. It's not quite as exciting as waiting for Christmas.
Ken, where is your interior light in the 1990 Cab? Either mine doesn't have one or it's never worked since I got it.