Intermittent Dead Battery - Help

[Rodeo]

This is very odd. I have an 87 3.2 Carrera, runs great and is my summer daily driver. About 5-6 weeks ago, I left my office at the end of the day and the car was dead, no sign of life at all. Had my wife bring the jumpers and it started right up with a jump. Drove 10 minutes home, parked for the night, and it started just fine the next morning. It continued to start every day until this morning. Completely dead again. Its probably been 500 miles since the last (and only other) incident.

The battery is only 3-4 months old. The alternator was replaced with a rebuilt less than 5k miles ago.

Any ideas what could be causing this?

Thanks for any ideas you have. Steve

[Mark sP]

I dont know if this will help, but I suffered the exact same problem this month.

I thought maybe the alarm was draining the battery. Anyway, I replaced the battery and everything was fine until today. I sent my beloved to fill 'er up and got a phone call, "this old crock won't start and I'm stuck at the pump etc etc etc". The engine wouldn't even turn over. So I thought maybe the new battery had drained.

So I headed over there and guess what! It started first time. I got the car home and jacked her up. I discovered the gearbox earth strap looked very nasty where it bolts to the body.

I showed the nut a spanner, and the bolt sheared off in fright!!! So I cleaned up a new area and cleaned the end of the strap and reconnected it.

I don't know if this is the fix, but atm she is starting no probs. May be worth checking in your case too.

[magic930]

Charge the battery then check the voltage when the engine is running, I think it should be around 13.5V when the alternator is charging properly. Voltage regulator on the alternator may also have failed. Could be that the connections to the alternator were not done up properly when you replaced it.
Other thing to check is the transmission ground strap, remove it and clean the terminals. The strap is located on the passenger side at the front of the transmission. One way to check for a poor connection at the tranny strap before going to the trouble of jacking the car and getting underneath is to use a jumper cable anywhere on the engine block and find a good bolt on the chasis to ground it too. Also check your battery terminal connections since its new it may not have been done up tight enough.

[echrisconnor]

You also may want to check for some sort of phantom load. I'd turn the ignition off, pull the ground strap and put a voltmeter or ammeter between the ground and negative battery terminal. If you get a reading then you have something drawing off the battery. Pull fuses until the load disappears and then track whichever fuse cut the load back to the associated circuit.

When I first got my car, I ran into the same thing because for some reason if your turn signal is blinking when the engine is turned off, the parking light stays on. Now I make sure never to park with a turn signal in the indicating position.

[fuelie600]

My 87 does the same thing. I haven't had a chance to test the voltage regulator yet. (too many non-pcar projects) I did check for load, and it was small - basically the clock and radio memory. I have been disconnecting my battery when the car sits for more than a day. All of my connections are good and the battery goes totally dead.

I'm thinking voltage regulator. I noticed the negative battery cable was very warm last time I disconnected it, after a 30 minute drive.

[vash]

not all new batteries are good. i went insane checking everything on my truck, i even got desperate and posted here looking for help. turned out that i got a bad optima. i could have saved alot of money and headache by testing the new battery. EVEN the dealer (i got desperate) took the new battery for granted. they changed some harnesses and handed the keys over all proud looking, like they solved the puzzle. nope. what idiots we are were. start with the basics.

[Rodeo]

Thanks everyone for your help. Am taking tomorrow off, and will report back what I find. Steve

[john70t]

Batteries usually don't get "good" or "bad" from day to day.
They are a big electro-chemical sink made of alternate lead plate in acid set in a plastic shell.
The only way to get those symptoms from the battery is if a plate are loose and internally shorting.

Good battery voltage is about 12.6V fully charged.

Bad battery voltage is below 12.2V, which is less than 50% charged.
If this is so, make sure acid level is o.k.(refill with distilled water ONLY if necessary), remove from car (prevents acid-gasses messing up the paint), slow charge at 2amps setting until it holds 13-14 volts. Don't overcharge. DO NOT LEAVE ON CONCRETE. Check again another day while tilting etc. Should be around 12.6V.

Everything good=battery ok. Problem is something else,like a loose/corroded ground, or another electrical connection, or.......

[midlife]

Just a thought, but could it something left on? On mine, if the turn signal is left on, all the parking lights stay on, and if the wipers are left on it will drain the battery even though the wipers are not moving.

[Wil Ferch]

If you can constantly operate your power windows...even when the car is "off" and particularly if you've opened/closed the door...then you have a stand-by current drain. You should only be able to operate the power window after you shut down the car and not open the door. Once you opened the door, the circuit should shut off and you can't operate the P/W.

If you have this problem, it's likely a bad door switch that operates the dome lights. This triggers the P/W circuit.

Wil

[Mark sP]

Good catch Wil. I didn't know this! My windows work after the ign switch is turned off. However, once I open the door, then close it again, they do not work.

I thought it was a cool function, so that if you forgot to shut the windows, you could shut them without turning the ign back on! I often switch the ign off, open the door and then close the window!

Not wishing to hijack the thread, but can you offer more explanation into fixing this please?

ie. what is a 'dome light'?

Thanks
Mark

[scottb]

Originally posted by midlife
On mine, if the turn signal is left on, all the parking lights stay on

My understanding is that this is intentional. Apparently Porsche wanted to be sure that our cars wouldn't get crunched when parked on the side of a dark road. So, if you leave the left turn signal on when parking the car, the light stays lit to warn oncoming drivers.

[midlife]

Yes, I think it is common to some other German cars as well. It is a pain, as my signals do not self cancel. I've had trouble a few times arriving at work; Enter the driveway trying to not get run over by trucks, or srcraping bottom while rolling down the window and getting out the gate card. I forget about the turn signal, until someone calls with "you left your lights on".

[Mark sP]

All my 80's VW's and Audi's do this. It is normal. (I mean the lights, not the windows).

[steve911]

Mark--
its designed that way. As long as you don't open the door, the circuit remains live. Once the door is opened, windows should cease to function. You have to turn the ignition switch back on to get the windows to work again.
Nothing to fix - German engineering.

Originally posted by Mark sP
Good catch Wil. I didn't know this! My windows work after the ign switch is turned off. However, once I open the door, then close it again, they do not work.

I thought it was a cool function, so that if you forgot to shut the windows, you could shut them without turning the ign back on! I often switch the ign off, open the door and then close the window!

Not wishing to hijack the thread, but can you offer more explanation into fixing this please?

ie. what is a 'dome light'?

Thanks
Mark

[Joeaksa]

The turn signal is done this way on purpose in Europe. In many towns the cities are so full that there are no parking spots available in areas.

When someone goes into a resturant to eat and cannot find a parking spot they park next to the parked cars, in the driving part of the street. They leave their left turn signal lever on so that the outside turn signal light stays on to tell other drivers that there is a car in the street.

Done all the time. Took a while to get used to doing it. If someone needs to get out and you are blocking them, they just honk their horn and everyone gets up to see who is blocking and moves the cars.

Its a European thing...

JoeA

[Mark sP]

Well this gets wierder and wierder.

I just went out to check on this.

Unlocked the car, openned the door, both windows operate.

Get in and close the door, niether window operates until ign is switched on.

Open the door to get out and both windows operate again!

It seems as though mine is faulty.

Thanks for the input. (Sorry for hijacking the thread Steve).

[Rodeo]

I learned something here! My interior light activation button works only some of the time. Thought it was no big deal and that I would get around to replacing that little black button in the forward door jamb one of these days. But if I understand correctly, if I open the door and the light does not come on, the power to the windows remains on, waiting for someone to open the door. Would that alone cause the battery to drain? Just because power is available if needed?

Anyway, I probably should not admit this, but the battery terminal connector was loose. Not so it wold come off by hand, but loose. So I tightened it, jumped the car. Hope that was the issue, will see!

Thanks again, Steve

[Wil Ferch]

Rodeo...yep...that would drain the battery...

As to the others...I should clarify...the circuit I'm describing is certainly true for USA spec cars...can't say *for certain* if this same circuit is used for ROW ( Rest-of-World) cars....

Common fix is to replace the door jamb switch under the little rubber booty.

By the way...."dome" lights is USA-speak for interior overhead lighting.

-- Wil

[Wil Ferch]

Oh....if you park the car with the turn signal "on"...and shut the car off...only *one side* of the parking lights will remain on ( the side that the turn signals are positioned-on, left or right)...not "all" parking lights will stay on...as mentioned here by someone .

Wil