996Fever

Greeting all.
1986.5 automatic. Here's where I'm at right now. Just looking for advice as people have been to this point before I'm sure:

1. Went to start car after 2 weeks. Car dead.
2. Put charger on car, charger sounded funny. Stopped charging. Disconnected battery cables and charged battery.
3. Battery at 12v. Hook up cables. Large arc when seating negative cable. Cables start getting warm.
4. Remove cables from battery right away. Stop all attempts to start car.
5. Main cable to starter shows continuity to ground.
6. Visually inspect cable underneath. Cable not welded to anything or showing signs of distress.
7. Disconnect Main battery cable, Starter to Alternator cable, and smaller wire from starter.
8. Main battery to starter cable no longer grounded when unhooked from starter and alternator lead.
9. Main terminal on starter not shorted to ground with cables disconnected.
10. Battery put back in. Just main cable from battery to starter reattached at starter.
11. Ground connection in hatch inspected and cleaned. Battery terminals connected to battery. No arcing.
12. Battery terminals disconnected.
13. With everything still hooked up at the alternator, cable running from stater to alternator shows continuity to ground with meter probes standard or reversed.

Looking for advice or should I just remove the alternator and have it tested?
Any help is greatly appreciated.
Randy

Alan

Unfortunately what you described as diagnostic checks would happen on any normal 928.

There is always some current consumed at all times when the ignition is off - this is likely enough to fool an ohms (connectivity) measurement (esp. with doors open). There is also usually a spark when you connect a freshly charged battery due to this constant low consumption, interior lights & capacitance of the B+ wiring.

So this could mean you don't really have a problem - or perhaps you do. Best test is to connect the battery+ via a 10A fuse. if the fuse doesn't blow - you probably don't have a real problem - if the 10A fuse blows you do have a problem.

Connections from the starter go to the alternator (could have an excess current fault) and to the Jump post and from there on to the CE panel. If you have ABS the starter is also connected to the ABS Pump & actuators via the drivers side "jump post" (a little more hidden - but visible). Try disconnecting these in turn and performing the same fuse tests to narrow things down - be careful with all these B+ connectors - don't do any welding!

Alan

996Fever

I'll try the 10a fuse thing, that's a good idea. This was more than a normal battery hook up arc. It was more similar to what my welder would do if I just did a quick 1 second blurp with it, and within seconds the ground strap and main cable were on their way to insulation melting temps. Ground strap battery terminal burnt my finger while unhooking it. Also, battery holds a charge for a week afterwards, but it's sides swelled.
Randy

Shark2626

I have no idea what else may be going on with your car after this incident, but I really believe that your battery is very dangerous and should be replaced with a new one before you continue. Good luck, wear protective equipment.

996Fever

Yes, the battery has definitely been compromised. That's why I don't think all is well. Too bad, it was a real nice AC Delco battery that served me well for years.

buccicone

"Many Years"? They do have life expectancy 3-5 years minimum. I just replaced a Duralast Gold (Autozone) after 10 years in one of my trucks. My experience with Duralast is very good.

Alan

I think the battery may still be fine. It depends how long it was connected. Take it off and charge it again on a good charger then see if will it retain charge OK with good terminal voltage.

After charging measure the terminal voltage, then after a day (off the car) measure it again. What does it start out and and where does it end up?.

Try disconnecting the front of engine B+ connections: starter, alternator, ABS, Jump post - then measure to see if the harness B+ connections are shorted to ground.

Alan

Mrmerlin

I would inspect the ABS wire routing to the junction just infront of the PS tank and the alternator harness routing.
NOTE the ABS wire is always hot and unfused,
if you recently did a timing belt the chances are good this wire has been improperly routed and possibly shorting on a metal part.

928NOOBIE

If the battery's sides are swelling it's going to go. You need to get it the heck out of the car and away and cover it with a trash can or something and let it sit ...you sure don't want that thing going off while you're handling it....let it die away from everything....if I saw the battery in my car swelling out from the sides I would probably run and hide for about 5 minutes first to make sure it wasn't going to detonate right then and there....I'd be so scared honestly to go back in there and pull it out....get a big heavy tarp or something or an acid proof bio suit or something...that freaks me out just thinking about it....please get rid of that battery

GregBBRD

I've got a pretty good idea of what your problem is, from your description:
A completely dead battery can be charged backwards, so that positive becomes negative and visa versa.

I've seen a couple other Porsches, over the years, with this mistake.
The first one I traced was difficult to figure out and took some serious thinking!

The main "short" is always....the alternator. And it rarely survives this abuse.

Tough on other parts, also....
Radios rarely survive this, if it was turned on.

Most other electrical stuff survives, because the "arc" to the post is so severe that no one gets a chance to turn much on.

The Forgotten On

^^ My guess was going to be failing diodes in the alternator. That is the only thing I can think of in that current path that can cause a dead short other than the wire itself.

The alt can be rebuilt fairly easily and economically with a new set of diodes....

But yeah, if your battery is failing like that, get it the hell away from your car, house, and anything you care about. There was a thread recently about a battery that blew up IIRC. Definitely not a good thing to have happen.

GregBBRD

It's no a matter of the battery failing...it's all about reversing the polarity of the battery.

996Fever

Hi, Sorry for the delay. Ive been gone for the week for work. I did do a timing belt as MrMerlin asked, but it was 2 years/1500 miles ago.
The old battery would charge to 12.something volts, after one day it was 10.20v, after a week it was 10.09. Probably enough to start a car, but I bought a new one anyways.
Rehooked everything back up at the starter, put the inline 10a fuse into the B+ line as Alan said, and it blew the second is was connected, once again with a large arc.
As I said earlier, with everything past the starter disconnected, and the B+ wire hooked back to the stater, no fuse blows, so I'm pretty sure it's not the starter.
So I guess I will unhook everything past the alternator, leave the alternator hooked up and see if it blows again. Or should I just remove the alternator and have it tested?
I see the screw terminal for the ABS in front of the PS res. That looks easy to get too. Is the ABS ever at fault for an issue like this?

Randy

Mrmerlin

disconnect the battery before you remove the bolt for the abs wire or you will weld the screwdriver to the fender
see if the wire is touching ground.

NOTE follow that wire see if its shorting along its run it might be time to add a sheath of heat shrink to that wire

Alan

Well - fuses are cheap - so try different configurations - with just ABS, with just Alternator, with just jump post - figure out what is causing this.
I'd do that before taking the alternator in for testing.

Alan