Oldtee

My daughters 87 Carrera cannot seem to keep the battery from going dead in short order. It is a new battery, one year old. I have pulled every fuse looking for a drop in amp leakage but no joy. I am convinced that it is related to the car alarm but I am reluctant to start cutting wires. Anybody run into this problem and can pass on their solution for me to try.

Thanks

wwest

It isn't inconceivable that your new battery is faulty.

Steve Weiner-Rennsport Systems

Many reasons for battery drainage but the first places I'd be looking are:

1) Make sure the alternator puts out 13.5v at 2K RPM.

2) Make sure the battery cable connections are clean & shiny at BOTH ends. This means both cables on the battery and the ground cable at the transmission.

2) Using a digital VOM, check for current draw when the car is off. Aftermarket alarms are one of the worst offenders, but check EVERYTHING.

Good luck,

Oldtee

Thanks. Just picked up the car.

Bat voltage no load was 11v

Once started. Charging at 13.7 idle to 14 on the road.

10 minute drive was enough to put some juice in bat and car would start.

Have it on the charger now. Will to a leak test this PM

Cables are clean.

Will take the battery for a load check tomorrow.

Then I will make an appointment to have the stupid alarm system removed by someone who knows what they are doing.

I gotta find and fix this. I can't leave her without a reliable car. She knows my phone number!

Oldtee

Every damn time I think I know something, I find I don't.

The ma draw is between 34 and 36 pulsating. I would expect a steady #.

I did a load test on the battery. It has been charging for several hrs at the 2a charge rate (rather than the 10a setting).

The load test with 15 seconds indicated 'weak' but at the bottom of the green.

Then I hooked the charger back up with the ground off. The mistake was I put the ground on the ground cable, not the battery. The 'charge complete' light came on. Ummmm. Then I put the ground back on the - terminal and it began to take the 2 amp charge. Wonder what that was all about.

Anyway, 35ma drain is a bit too much. I was looking for less than 15ma.

Comments??

User 4221

The pulsing condition indicates a bad ground. Especially when it disappears when connected directly to the battery.

It may not hurt to do a ground maintenance by cleaning all grounding points. I did this on an old 928 and the results were amazing. The lights worked better and the instrument voltmeter read more steady.

On the alarm, I would just find the controller unit (usually under the dash or behind the carpet in the trunk) and unplug it. This would remove it from the ckt w/o hacking wires. The PO of my car complained of a battery drain so the first thing I did was remove the alarm and the vintage 1990 mobile phone system. I get no battery problems at all.

HTH,
Scott

Oldtee

Thank you for your response, but I'm wondering if you could explain how this could be. Remember I am doing a leak test. The digital ammeter is hooked in series with the battery. The reading is pulsing at a rate about as fast as you can say one, two, three, four ......

The digital voltmeter does not vary when the car is driving. I didn't hook a scope to the line (don't have one) so don't know what ac may be present.

Steve Weiner-Rennsport Systems

Try this:

While watching the VOM, pull each fuse one at a time, and observe the display to see any changes as you disable each circuit in the car. That includes the power to that alarm system.

Oldtee

I already did this, no joy. It must be fused somewhere, it isn't in the main fuse block. Gonna look further.

SPDADCT

I was replacing the battery every year as well even switched to Gel. My mechanic said the alternator was passing all the necessary tests and outputting 13.7 volts. I always believed the alternator being 20 years old is not putting out enough amperage to charge the battery. Recently the alternator went out all together and the new alternator has solved the battery going dead issue.

If it's a weekend driver as my car is, I am using the Porsche Cigarette Battery Maintainer. This works great to maintain the battery during storage.

theiceman

a couple of things come to mind here ....
does the 87 have fuses in the rear like the SC ? the pulsing to me does not indicate a ground issue at all but more of a bleeding component , which would cause your issue .. an Alarm yes, but things like this can also be caused by other things .. rear defroster for example .. although i think that is switched. The other thing that can cause this is a bad diode in the regulator ( part of your alternator ) bleeding back and draining your battery, basically it could be a bad bridge rectifier.

Steves suggestion is an excellent one , just make sure you have checked all the fuses.. If you truely do have them all then I would think your alternator is bleeding the battery .. see if you can leave your meter on and take the alternator out of the loop .

This is all of course after you have ripped out your aftermarket alarm.


Good luck

Oldtee

Some good information in the posts here. Never thought about the fuses in the back. The Alternator is 1 year old so will save that for last, after the alarm system is deep sixed. Also am going on a search for other fuses. Battery is fully charged now, was on the charger last night at 2a slo charge.

Thanks for all the head scratching you guys are doing. When I solve this problem will report.

User 4221

There are also a few inline fuses under the carpet near the battery that need to be checked.

BTW, a pulsing current profile seems like a capacitor that is charging/discharging. Ignition system maybe?

Just a thought.

Oldtee

I am buffaloed big time. After another load test on the battery, which indicated good, I went to check again any battery leakage. I got none. The battery is fully charged, the meter is a Fluke (bought before they got cheap). While I don't pretend to be the brightest bulb in the factory I am an old school electronics technician trained in the vacuum tube days so I thought I knew the basics. Why would a partially charged battery leak while a fully charged battery doesn't?

The problem with a little knowledge is the result is a little diagnosis.

I have gone through the schematics in Bentley. Suspects are: DME control relay, Radio, anti theft control switch, two tone horn relay, front fog lamp relay, power window control unit, starter switch, starter and alternator, drivers seat stuff, oil cooler fan relay. These look like they are hot all the time. Some are fuses that I checked.

So... what am I looking for? Battery at 11 volts I get a drain. [Battery at 12.4 volts, no battery drain.]
THIS WAS INCORRECT, MY FUSE BLEW ON MY FLUKE. A relay that does not sense with full power but drains with low power. I am getting the feeling that I have a 928 on my hands.

The original plan, IE to rid myself of the alarm system first still holds. THIS WAS DONE TO THE TUNE OF $100, IT REDUCED LEAK TO 24MA Then run for the winter and watch carefully for signs of a weak battery. Next will be to unplug (if I can find the thing) the central locking system ecu.

Wish me luck.


NOTE EDITING INFORMATION IN CAPS

oldskewel

Weird. Just the sort of thing that a bad battery might do. Intermittent behavior, etc. One way to "separate variables" while you're banging your head on this would be to charge + test (over time) the battery after disconnecting it from the car.

Here's my possibly related story:
I bought an Optima battery probably 10 years ago to make sure I'd have no acid leakage/rust issues. That battery was later transferred to a second car that was later sold, and I bet it is still working.

The battery I replaced it with was another Optima (same model - red top). Within the first year, I started having intermittent non-starting issues. When this happened, it would not start at all (no solenoid click or turn-over) even though most electrical systems seemed to work OK. But the instant jump-starting cables were applied, it would fire up just like it's supposed to. I cleaned every contact, measured current drain, replaced ground strap, ground cable, and some relays just for good measure. All with no effect.

Finally I concluded that it was the battery. I took it out of the car. Charged it, then would check the voltage a day or so later. Should be 12V, but was < 11V. Since I had such a good experience with the first Optima, I incorrectly doubted everything else first.

Fortunately, I got a totally free replacement on warranty since it was within 3 years (actually 37 months I think, but the Pep Boys guy I bought it from did the swap for me). Zero problems since doing that ~6 months ago, where I had been having at least 1 problem per month prior to that (light usage).