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Old 06-04-2012, 04:04 PM   #1
L84THSKY
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Default Battery light coming on dashboard

Hey guys

My latest issue. Was driving back from upstate NY Sunday evening after Mountain Biking and the battery light started flickering. I noticed when the car was idling, the light was on, but when I revved the engine, it would go out. Was a bit paranoid till I got home. Turned the car off, measured battery, and it was 12.7V. Started the car and it was about 12.8V. Looks like a bad alternator to some degree. If the alternator was totally dead, I wouldn't have made it home just on battery, besides, the battery was not low when I measured it at home. Then I disconnected the negative and did a current leakage check. The meter said 1.2A; this indicated a short somewhere.

Now, I just replaced the cam positioner sensor on Friday, and I was worried I had shorted something when screwing around under the intake manifold. Maybe a total coincidence, but who knows.

So, either I did short something, the alternator is bad, or a bad ground harness. If the ground harness was bad, I think my battery would have drained over night, and the car wouldn't start, but it starts fine. All electrical components work fine, without any dimming. Since the alternator is original with 157,000 miles on it, I think it was due for replacement anyway. I just removed it and brought it to an alternator rebuild shop down the block.

After reading comments on how long it takes, and what needs to be removed, here is my two cents. Remember, this is an original unit, having never been removed. The whole removal took about 30 minutes. Unbolt the power steering reservoir, and move it out of the way. Remove the two alternator bolts and leverage the alternator off the brackets. In my case the bottom of the alternator was wedged good in the bracket. So to make things easier, unbolting and moving aside the secondary air pump was a good idea. By doing that, you can then jostle the alternator side to side, until the alternator is free from the lower bracket.

I hope the shop finds a problem with the alternator, otherwise I may have to start really digging in deep to find the cause.

Any thoughts on my problem are welcome.

Eric
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Old 06-04-2012, 08:05 PM   #2
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Most likely the diode pack in the alternator.

It is probably easiest to do a replacement.

Maybe shoot some pictures of the installation and we could add something to the data base for new members doing this.
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Old 06-04-2012, 08:19 PM   #3
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My alternator went out at 163,000 miles with similar symptoms - the battery light came on but would go out at high RPMs. I was about 100 miles from home and drove back at something like 4,000 RPM to keep it alive. The car started to die literally as I was driving down my block.

Never did any other diagnostics. Just put in a $99 rebuilt unit which has been running perfectly for the last 4+ years and 55,000 miles.
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Old 06-04-2012, 08:55 PM   #4
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Default Update

OK, got the news from the alternator repair shop, brushes were toast. They rebuild it in about 90 minutes, and handed it back to me. Threw that baby in and fixed the problem. Total rebuild cost was $125.00, and they make it look like new; much preferred than a rebuilt from some automotive chain.

Here are the measurements:

Battery voltage
before 12.7V after 12.7V

Battery voltage car running
before 12.8V after 14.45V

Current leakage
before 1.2A after .1A

The numbers speak for themselves.

I could do a write up, but I'm already done, and very lazy. Just unbolt and move aside the steering reservoir and secondary air pump and the rest is easy. No special tools, just 11mm 13mm and maybe one other similar sized socket.
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1998 (July) 318ti, 5-spd
OEM Armrest • Blaupunkt Heidelberg CD50 CD Player/Compact Drive MP3 Player • Diamond Audio 5.25" rear speakers • Navman ICN 530 GPS • BMWALARM.COM (with comfort settings) after market alarm system • Magnecor 8.5mm wires • M-Z3 Shifter/Momo Knob • Burlwood Dashboard • Stromung Exhaust • X-brace • Racing Dynamics Front Strut Bar • Carbonio C.A.I. • 17" Rial Rims • Vader Seats/Heated/Lumbar Support • M-tech Steering Wheel/Front Sway Bar/Front & Rear Bumper • Depos/w 6500K Angel Eyes/6000K HIDs • Clear Corners • M3 Mirrors • UUC Light Weight Flywheel/M5 Clutch/M3 Clutch Slave • E28 3.46 LSD/Mcoupe Cover/E30 Flanges & Halfshafts • UUC S.S. Brake/Clutch Lines • Hartge Roof Spoiler • BavAuto Springs• Bilstein Sport Struts/Shocks • E46 M3 Rear Shock Mounts • SPC Front Camber Kit • Reiger Hatch Spoiler • BavAuto Rear Camber Kit • Dinan Stage II Software • Turner Rear Sway Bar Reinforcements • BMW E46 Auto dimming mirror with Clown Nose alarm • Engine Compartment Light • Heated Wiper Fluid Retrofit • OEM Fire Extinguisher • Da'lan Trailer Hitch • Rear Sun Shade • OEM Fog Light Retrofit • H & R MZ3 Rear Sway Bar/ UUC Adjustable End Links • Cruise Control Retrofit • On Board Computer Retrofit • M3 twistie style side skirts • Carbon Fiber Hood
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Old 06-04-2012, 09:08 PM   #5
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Glad it is sorted, and the price sems on par with a replacement unit.

I used to have a shop doing starters and alternators for me, but they closed down...
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Old 06-11-2012, 02:20 AM   #6
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Your battery voltage with the car running says it all -- classic symptom of aging alternator.
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