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DISCUSSION => Electrical => Topic started by: BMWTarg on June 21, 2009, 11:27:21 PM

Title: 1991 318 IS batt drain
Post by: BMWTarg on June 21, 2009, 11:27:21 PM

Hi, I have a 1991 318IS that has a brand new batt in it. The car ran for a day and a half until tonight when it just died. It will take a jump and run fine, but will not stay running on it's own. My limited knowledge says that its the alternator... Am I right or is there something I 'm missing?
My thought is that it was just running off the battery until it drained it off. When running the headlights do not flare up when the car is slightly reved up.

What should I expect to pay for a new Alt?

Thanks guys,

Title: 1991 318 IS batt drain
Post by: 1991 E30 M42 on June 22, 2009, 01:45:08 AM

I have a used one if your interested

Title: 1991 318 IS batt drain
Post by: HATER-PROOF on June 22, 2009, 03:16:30 AM

I would kinda take 91 E30 M42 up on his offer or head to your nearest junkyard if you're tight on cash.

Title: 1991 318 IS batt drain
Post by: BMWTarg on June 22, 2009, 04:27:44 AM

I take it you guys think it is the alt as well?

Title: 1991 318 IS batt drain
Post by: DesktopDave on June 22, 2009, 07:06:06 AM

Might be the battery too.  Even if it's brand new, it might be defective or internally shorted.

I'd take both the alternator and battery to Pep Boys or Advance Auto.  They'll load test the battery and do a somewhat thorough test on the alternator.  A reman alternator for these cars is a fortune!

Could also be a short in the car's wiring.  I've seen bad shorts flatten a brand-new battery in less than eight hours.

You also really need a multi-meter.  Harbor Freight has really cheap ones starting at $4.99.  I'd personally spring for Radio Shack's mid-priced model...probably about $60.  The best money you'll ever spend on a car is for the right tools.

There are a few ways to test the battery & alternator if you can't get it to a load tester.  You should see slightly more than 12v on a battery between the terminals when the car is off.  If the car is running, you should see more like 13.5v.  You can also test the diodes on the back with your new multimeter.  Just google it...most alternators are pretty much the same...it's all out there.

Title: 1991 318 IS batt drain
Post by: RED IS 91 on June 22, 2009, 07:33:50 PM

Get a Multi Meter at Sears or a car parts store .When the car is running you should have at least 13 volts at the battery when you connect your new Multi Meter to it. If you don't then you'll have to check the alternator .
Report back your findings and we can help further.

Title: 1991 318 IS batt drain
Post by: BMWTarg on June 23, 2009, 02:43:35 AM

Thanks guys, I will let you know what I find