DeskFX

Hi everyone,

I'm new to this forum but I've had my 88 928S4 (automatic) for about 5 years. Its mostly a weekend car and gets stored over winters. I'm on my 4th battery in 5 years.

Something keeps draining the life out of the batteries to the point that they are ruined. I have no other electric problems except this one. Are there any known causes for this?

I should mention that the previous owner installed a remote starter. Its switched off, but I wonder of this may be the cause.

I'd appreciate any help.

Thanks

MikeN

How fast does your battery drain to where the car will not start? 928s in general don't like to sit around.......All three I have owned were in danger of starting if I let one sit for more than 3-4 weeks.
They "should" go longer......but I haven't seen it.......especially in very cold or hot weather. I just put mine on a small charger/maintainer and its always good to go.

sublimate

Subjecting a discharged battery to cold is the primary cause of battery death. Keep it on a trickle charger when you store it over the winter. You can hook it up without removing the battery.

rixter

a local friend of mine had the same problem, finally traced it to a bad groundstrap on the battery...

tresamore

I also read somewhere on here quite awhile ago about a diode failing in the alternator causing a drain.

Mark

You can hook up a VOHM meter in-line with the battery (WITH THE CAR OFF) and start pulling fuses to isolate where the extra draw is coming from.

Bill Ball

The 928 has a small parasitic drain normally of about 30-50 miliamps. That will drain any battery over a month, so the battery should be disconnected during winter storage or a trickle charger should be connected. If your battery is draining faster than that, you need to locate the circuit involved by one technique or another, such as Mark suggested. My 89 had a faulty door lock solenoid that was draining about 200 miliamps. Classically, bad pin switches (glovebox light) or aftermarket alarm/radio electric hacks are involved, but it can be a myriad of possibilities, including a few things that are not fused on the central panel. If you find the current draw is more than 50 miliamps, pull all the fuses on the panel. If the drain is gone then reinstall one-by-one. After the circuit is located, then you need to look at the electrical devices on that circuit, disconnecting them one at a time in hopes that the bad one can be found this way, although it may require testing for shorts.

Jim bailey - 928 International

Batteries do not like to be deep cycled in normal driving they stay full and fuller. The simple option is using a trickle charger battery maintainer which is what Porsche recommends that the dealers do for ALL the new cars. You should determine how high the drain is and attempt find it if it is much higher than what Bill describes.

Steve 88

Could someone with extreme patience slowly walk through the process for testing battery drain with a multimeter? I have read the battery drain posts on Rennlist and have gone to the external links on multimeter use and still cannot get a reading. I have tried using both my older analog and my new digital multimeter, both of which work fine for 928 voltage checks on battery/alt and resistance. I am completetly stumped. Instructions suitable for a 12 year-old, please. I cannot be insulted.

Thanks

Fabio421

928's have these issues for some strange reason. Everyone seems to have a different cause of the drain. Mine turned out to be a bad glove compartment light switch that allowed the light in the glove box to stay on all the time. I was lucky and found it but others haven't been so lucky. The best way to narrow your search is to do exactly what Mark said. Disconect your negative battery cable and hook up a volt meter in line between the ground post on the battery and the actual ground cable. You should see a voltage reading on the meter. Make sure your interior lights and door contacts are all closed and off so you aren't chasing phantoms. Start pulling fuses one at a time. Eventually you will get to the one that protects the circuit that has the drain. When you pull this fuse you should not see a voltage reading on the volt meter anymore. Now you know which circuit your problem is located. It will still require a little detective work on your part but at least you know where to start. You can also use a test light instead of a multi-meter but a multi-meter will tell you exactly what voltage is being used. If you think you may have more than one thing draining the battery you might want to use an amp meter . It will tell you how much current is "flowing" and you will see a drop in the amps being used when you pull a fuse out of one of the offending circuits. To simplify what I just wrote. If drain A draws 10 amps and drain B draws 5 amps but they both draw 12 volts you wouldn't see a change in voltage if you eliminated one of the drains. But you would see a drop in amperage if you were using an amp meter. I hope I explained this well enough. If not let me know and I will try again.
The battery disconnect is a last resort. The PO probably just gave up on finding the problem. As far as the alternator drawing current when the car is off. Yes this is a possibility. You can take the alternotor out and have the diode replaced or you can add an aftermarket one externaly on the alternator. Good luck. Its a pain in the $#@ to find but very rewarding once you do. Most people give up.

worf928

For 'drain' checks you want to measure current. Put down the multi-meter - even though it claims (read the fine print in the manual) to be able to measure current - go to Sears/Radio Shack and buy one of the inductive ammeters - the kind that have a spring-loaded 'loop.' You close the loop around the wire that is carrying the current you wish to measure and look at the display. Easy as pie.

Beats the heck out of messing with the multi-meter, crossed prob wires, fragged fuses in the MM....

SharkSkin

Another twist in the story; you should connect your ammeter to a ground point on the body and to the negative battery cable BEFORE you disconnect the ground cable. It's important that the power never be interrupted while performing this test, because some drains will disappear once you disconnect the power. For example, you may have a relay that remains activated due to a feedback loop in the wiring. The second you disconnect power, the feedback loop is gone and you're left scratching your head. I've seen this happen myself and know of several people it has happened to over the years.

Jim bailey - 928 International

Also note that the red door safety lights illuminate when the doors or rear hatch is open. So simply turning off the interior lights leaves those lights on.

dr bob

If you go this route, BE SURE to get a clamp-on probe that's rated to read DC current. Most of the common clamp-ons are just induction/transformers with a meter in series. To measure the DC field, the meter needs to generate its own field, then let the DC current distort it. This means more complexity and more $$ when you buy.

For a safe method, get out your soldering gun and attach a couple wires to a regular car light bulb. You can buy a "HELP" bulb socket at pep boys if you don't want to solder. Install the bulb wiring in series with the battery ground lead. Lift the ground lead from the frame in the back, one bulb lead goes to the disconnected strap, other goes to the frame. Light is brighter with bigger drains. If you want to measure relative current with the meter, install it in series with the bulb. Once you've found all the stuff that makes the bulb glow brightly, and the bulb is dim, you can take the bulb out and use just the meter.

Take this an extra step, and make a bulb tester with two spade lugs on the end, or hook them up through a 'used' fuse body. You can then plug the tester into a fuse socket to see if that particular circuit is leaking current to ground.

When testing, remember that there are bulbs in the door edges that stay on even when all the interior lights are turned off locally. Working with the door or hatch open will cause a drain.

Be aware also that you need to take the key out of the ignition when the vehicle is parked. Turning it to off but leaving it in the lock is not enough.

worf928

Good point Bob. I don't remember how much the one I got cost. (Less than most 928 parts though.) But, the 'needs to do DC' was a requirement I left out of my description.