Strange Mazda electrical issues

[drscope]

This is a new one on me.

A friend of mine has a 1994 beater Mazda 626. It’s completely worn out. But it’s paid for and in his line of work he uses it every so often when he doesn’t want to be seen driving his nice car.

The rear brakes went metal to metal several months ago and he recently got around to asking me if I would replace rotors and calipers. No problem.

Well before he dropped it off the battery went dead. And he didn’t want to go through the expense of brakes if this thing was going to need anything more then just the battery. So he went and had the charging system checked out. It checked out just fine, so he replaced the battery, and a couple days latter dropped the car off to me.

I did the brakes and everything was fine. So today I was going to deliver the car back to him. When I started it up it turned over a little slow then fired. Seemed strange but I’m not familiar with this car so I don’t know how it normally acts.

I drove about 2 blocks and then hit the electric window switchs to put the windows down. A minute or two latter it started bucking like it was running out of gas. Gas gauge says ¼ tank, but again I’m not familiar with this car so for all i know it could be empty.

I pull over and the engine stops. Turn the key and all I get is faint dash lights, not even a click. I’m on a hill (it’s a 5 speed) so I get her rolling and pop the clutch and it fires up. I turn around and head for home and it starts bucking and again.

There's no volt meter or amp gauge on the dash and I didn't have a battery or alternator light on, so I'm not getting any info on the charging system.

I made it back home and left the engine running and went and got my volt meter. At the battery I’m getting 6.4 volts. Rev it up and nothing changes – still 6.4 volts.

I figure the alternator must be fried, but it was just checked out and was OK. I shut it off and go to look for my battery charger. When I get back to the car a few minutes latter, I notice that the numbers on my still hooked up volt meter are climbing. It’s at 10.2 volts and as I stand there watching the numbers continue to slowly climb.

The engine is off, there’s nothing charging the battery! But it’s charging itself. I’ve never seen that!

A call to the owner and we think it has something to do with the windows. But I figure if it had a short that bad in the window wiring it would probably have blown the fuse.

I’m scratching my head on this one. Anybody have any ideas?
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[Erik G]

check the fuses by pulling them and inspecting? Maybe its just me, but I have seen fuses melting and not blowing nowadays. Kinda scary... I figured made in china fuses?

[minger]

File a patent for your new perpetual motion machine then license the 1990 tech to Tesla.

Mouse gnawed partway through a wire and gravity/heat/motion/the probing after parking jostled the connection enough to start getting better?

[minger]

New idea: coincidence that your volts are multiples of 2? Something internal in the battery. Dead/dying cells and the stirring of the battery from the heart and motion improved the internal connections.

Since it is your problem, I find this interesting. If it was happening to me, I'd be angry.

[busdaddy]

I recently had a Honda alternator from the same era check out fine in the shop but not charge on the road, same symptoms as you describe, replacement alternator solved all the issues.

As for the climbing battery voltage it's not suprising since it's a newish battery and you had just removed the load/discharge.
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[richardc]

A good battery will do that. Charge battery & check charging system.
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[drscope]

I'm 99% certain the alternator has quit. It's mainly just the rate of how fast the battery drops volts when the engine is running and then seeing them climb back up when it's shut off that is a little strange to me.

But it just left here on the tow truck to go back to the place that said the charging system was Ok. So it's not my problem (I did my part) but I would like to know what the cause is.

Tow truck showed up before I had a chance to test the alternator.
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Mother Nature is a Mean Evil Bitch!

[modok]

Maybe the rectifier in the alternator is dying. That sort of part sometimes works ok when cold but not hot.