Eddie911

Every day I drive my 90 C4 and it keeps getting better. Evcery morning I get in and the car won't start. I do have some battery life as the lights work (although a little dimmer than usual) but there is not enough juice to start the car. I have checked all door contacts and the lights are turning off. Any ideas on how to find the source of the drain??

Drew_K

Eddie, it could be as simple as a bad battery and/or alternator. Based on my 92 C2's records, my car seems to need a new battery every 2-3 years. If you haven't already, I would have the battery and charging system checked out.

I've heard that the alarm can be a major battery drain, but that shouldn't be a problem if you're driving the car every day.

Does your car have the factory stereo? Reason I ask is that I've read that there is an alarm wire connected to the factory stereo that must be dealt with if the stereo is replaced. As I recall, that alarm wire can cause the battery to drain, but I'm sure someone else can fill in the details.

If you can't figure out the problem (although I suspect it's the charging system and/or battery), consider having the dealer check the car out. I had an electrical problem with my 92 C2 when I first bought it. Both of the main local independent Porsche mechanics couldn't figure out the problem, but the dealer figured it out right away with their diagnostic equipment. Problem solved and the car has run like a champ ever since.

Good luck,
Drew 92 C2

Adrian

Dear Eddie,
There is a way to at least attempt to discover if you have a genuine current drain. Remember that you do have some usage of the battery by the DME, Alarm etc.
Firstly you disconnect the negative terminal of the battery. Then to make myself happy I disconnect the positive and reconnect the negative. I then put a multimeter set to 10Amps current in series between the battery post and the cable connector. You should read between 8ma to 13ma and if you have a hefty stereo system, maybe up to 20ma. Ensure you lock your doors to activate the alarm. Record the figure. If the figure is more than 20ma you have a current drain. To be quite honest you will if you have a current drain read figures like 0.5amps or in my case, 2amps.
So now assuming you have established that you do indeed have a current drain it is time to find out the cause.
Unlock the doors now by the way. Saves the battery (joke).
Open up the central electric. (Fuse panel).
Ensure the multimeter remains connected. Using the fuse extraction tool start with either fuse Number 1 or at the other end. Pull the fuse and see if the current drain falls. My problem was on fuse 38. The radio booster.
When you have finished this check and regardless of your findings, you have to reconnect the battery, start your 964 and go for a minimum 15 minute drive. You have reset the DME by doing this and you have to get it re-adapted.
Now a couple of other checks you can do.
With the engine off and everything hooked up, use the multimeter and record the voltage across the battery. Start the engine and at 1200RPM record the battery voltage again. Should be 13.8VDC minimum. Let the 964 idle and record the voltage again. If less than 13.8VDC this indicates an impending alternator failure or a failed battery.
Shut the engine off and read the voltage again. Should be around 12.4VDC. If less than this then the battery was too flat (what was the first reading) and is not charged fully or the alternator is not charging or the battery is kaput.
Hope this helps but this you can do yourself,
Ciao,
Adrian
911C4

Eddie911

Ok, here is what I know (I should preface this by saying I am mechanically inclined but not an automobile expert). I checked the voltage before doing anything with the car off at the battery and it showed 10.05 volts. The car will not start. I then disconnected the battery as per Adrians instructions and when I did a voltage check when it was not connected it showed 11.51 volts. As soon as I reconnected the battery, it went back to 10.05 volts. I then tried Adrians test. I use a Radio Shack multimeter and set it to 200 ma setting (it is digital so I assume that even though adrian said 10ma I should still see something)the only setting for ma available. It reads 0.00. Maybe I hooked it up wrong? I had the battery post connected to one lead of the multimeter and the second lead of the multimeter going to the cable. Not only did it not show any readings, it did not allow any current through as was evident by the fact that I could not unlock the doors. Funny thing, I set the meter to DCv with the same config and it showed 11.5 DCv. HELP !!!!

Adrian

Dear Eddie,
You normally have to move the red lead to the 10Amp connector or socket on the multimeter. I have three multimeters and all of them have their own 10Amp socket which is fused.
You may also have to select amps elsewhere by a slide switch or something as well as selecting the range.
10.5 volts connected and 11.5 disconnected shows a pretty healthy current drain.
Ciao,
Adrian
911C4

PS: To me healthy current drain is a figure of Electronic/Electrical engineering speak.

Eddie911

Ok, I bought a new multimeter that has the right connections. I put the red lead into a socket "10A" and the balck lead into the socket "COM". I disconnect the battery as per Adrian and hook up the meter and get a reading of 0.95 when the selector is set to "10A/20mA". I had to boost the car and drive it to the store to get the meter so that may have some impact on the numbers.

Adrian

Dear Eddie,
Due to time zone difference we are going to have a lag here in answering. Sorry about that.
Anyway, you have what I suspected, a 1 amp current drain. You need to find the source of this current drain. Start by pulling the fuses one by one and please let me know what you find,
Ciao,
Adrian
911C4

PS: Eddie just to make it clear this test is done with the ignition "OFF" not "ON". A current drain is a loss when the power is effectively removed from the 964. Driving to the store, boosting the battery will have no effect on the drain figures.

Eddie911

I did what you suggested. I set up the meter and pulled fusues one by one. When I got to #11 (inside lights and clock) the drain reduced to 0.22 from 0.94. I then realized that I had the hood open to do this test. When I manually pushed the hood contact closed, with the #11 fuse in, the meter read 0.22. I then closed the hood with the meter outside (to make sure the contact was working) and it remained at 0.22. Therefore, I have determined that a)the actual drain on the battery is 0.22 and not 0.94 and b)I removed every fuse and could not get the 0.22 to change. Again, the battery was almost flat this morning. The radio works, the interor lights are dimmer than usual, but the car won't turn over(it tries but not enough juice).

What next???

GeoffD

Gents,

It is funny how this topic pops up periodically and almost always concerning C4's! I had the same problem on my 89 C4 last winter and carried out all the diagnostics on the way to discovering that I don't have a huge drain problem (although the car clearly did at one point because when I removed the HVAC head as part of the investigation, I discovered that the lead to the little air sampling fan on the back had been disconnected because with it connected, the fan never shuts off!)

Anyways, after completing all the diagnostics and still not finding a major problem, I just replaced the battery (out of frustration) in April and the car has been a trooper ever since. We'll wait to see if that continues during the colder weather.

Adrian

Dear Eddie,
The 0.94 is with the hood light on. I recommend you remove the light bulb. It is possible for the light to come on (not necessarily related to now) and I recommend to remove this bulb.
Okay, based on your figure of 0.22 amps, this is far too high. This is 220ma and you are looking for 20ma or less. This means in 5 hours 1 amp is removed from your battery.
I would recommend you start the 964 and check the alternator output voltage. Is the alternator charging properly at 1200RPM, 13.8VDC min.
I know the old clock can cause a problem like this. It is rare but it can happen.
I would certainly get the battery capacity checked. However these current drains can destroy a battery over time any way.
Other areas known to have caused problems in the past are,
AFTERMARKET ALARM SYSTEMS. These are often individually fused. Look for inline fuses on alarms, door openers, radios etc etc.
Oh nearly forgot. The alarm system is not fused via the central electric. It has its own fuse and boy is it tough to get to. However pull out your radio and check that the green wire attached to the radio rack is insulated from the rack on a special post and if it is missing, look for it and try and make sure it has been insulated.
The other puppy to check is the glove box switch and bulb. This also forms part of the alarm system.
Lastly you can remove the screws holding the central electic down. Lift it up and carefully turn it over. Corrosion underneath can cause the same problems.
Ciao,
Adrian
911C4

PS: The comment about C4s and current drains is not entirely accurate. These problems encompass all 964s from 1989 to 1994. I have many on file.

Eddie911

Today is Happy Day. A huge thanks to Adrian. I appreciate all the time you spent walking me through this. I had the battery checked; all ok. I then decided to do the fuse thing again. This time, when I removed #11, the drain went to 0.02. This is interior lights and clock fuse. I thought "where are there interior lights?" Oh ****, the glove box. It turns out that I had a power cord from my cell phone in the glove box that had worked it's way over the the contact and prevented it from activating when the door was closed. Took it out and now I am roaring around town in my Pcar. Thanks again, Ed.

Adrian

Glad to help Eddie. I love a happy end. Enjoy your weekend,
Ciao,
Adrian
911C4