Battery Problem

[brinkstar]

So I have had my battery and alternator tested and both come out saying they are fine, the battery has no dead cells, the alternator is reading that there is no problems. But heres my problem.

My car randomly will die. while driving (even if im driving for an hour in) the battery light will come on, and then the ABS light will start to flash on and off. if i turn the car off, i will need to jump it to get it to turn back on. When the car wont start, it just keeps rolling over. All the electronics work though, the stereo, the headlights, dome lights, everything, just the car wont start.

After i jump the car, it will work fine for about a week and then same problem will happen again.

As i stated i did have the battery as well as the alternator tested and no issues with either.

The type of add-on electronics i have in the car (if they may be causing the problem) are a 800 watt amp, 2 12" subs. and halo units with 7k hid lights.

everything else in the car is stock.

1998 BMW 328i.

[witeshark]

I wouldn't rule out an issue with the alternator being unable to keep up with that audio set up.

[brinkstar]

do you think getting a high output alternator would resolve the problem.

[witeshark]

I'd say so, just make sure to know what your electrical system specs can handle.

[CanadianWraith]

check your tensioner as well. i thought my alt. was dying as well turned out my tensioner was seized and the belt was slipping just enough that the alternator wasn't spinning fast enough

[brinkstar]

Ok so ive done a few things, and still having just crazy wierd problems.

I had a full test ran on my car, full electronics, full engin, NOTHING is coming back bad, no leakage, no bad belts, no bad alternator, no bad battery, nothing, BMW cannot find a SINGLE problem with my car. But every week i have to have it jumped, it last for a week then dies again. Ive tried now this week having everything unplugged that i possably could, no difference. Ive unplugged my amp and subs all together, put in my stock lights (disconnected the HIDs) took the stereo out. so basically ive tried running the car with less power then needed in the stock. I still have the problem. Ive noticed though that whenever i push a window up or down button, the lights go EXTREMELY dim and the RPMS drop big time. And what I believe is the alternator is making a really wierd sound when i do this. Im stumped, BMW is stumped. does anyone have any ideas what it could be?

[witeshark]

A similar weird problem in my friend's mom's Catera turned out to be a bad relay for the rear window defogger.