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3-Series (E36) Chat relating to the BMW 3-Series from 1992-1999. Autodoodad Specific models include: BMW 316i, BMW 318i, BMW 318iS/ti, BMW 320, BMW 323, BMW 320, BMW 324, BMW 325, BMW 328.

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Old 09-30-2004, 10:35 AM   #1 (permalink)
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Hi. I have a 5 speed, 1993 318IS with 27 K miles. I bought the car from one of my partners 3 weeks ago. The car is like new and has been regularly serviced by a BMW dealer.

A couple of days after I bought the car, the car suddenly died on me. It was late and I was stuck in the traffic. Then, the headlights and instrument cluster lights started to fade, ABS light went on, battery light also turned on. The gauges stopped working and the engine started to misfire and lost power. 15 minutes later, the car was completely dead. I thought I had a bad alternator because the car died while the engine was running, which doesn't usually happen if the battery needs replacement.

I checked the battery and found that it was toasted. No water. I asked the previous owner who confirmed that he replaced the battery 5 years ago. So I bought a new battery (Bosch, 900 amps, which is identical to the BMW battery except that it has 900 amps instead of 530 amps as the stock one). I had the alternator tested and it was putting out almost 14 volts at idle.

The car has been running fine for the last two weeks. However, yesterday night I noticed that the instruments lights were slightly dimming and the battery light went on twice for a couple of seconds, approximately 30 seconds after I started the car. The battery light then turned off and everything went back to normal. Today, the car started fine and the battery light did not turn on at any time.

Since I bought the car, I noticed that the brightness of the headlights and instruments lights seems to go up and down when the car is idling, especially when the AC and stereo are on. As soon as I accelerate, the problem disappears.

I have the following questions:

1. Do you think that my alternator or voltage regulator are to blame for this?

2. How do I know if I either have a bad voltage regulator or have to replace the alternator?

3. I believe that the voltage regulator is attached to the alternator, so if I buy a new alternator I assume that I will not need a new voltage regulator, right? Mercedes-Benz (I own a vintage 1969 280S) have a voltage regulator which is mounted in a different location and is not attached to the Bosch alternator.

4. My car came with a Valeo 105 amps alternator. Can I replace it with a Bosch alternator? Do I have to make any modifications in order to install a Bosch alternator? Same belt?

Your answers are greatly appreciated.
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Old 09-30-2004, 11:24 AM   #2 (permalink)
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The bosch alternators use a different mounting bracket or pully, I do not remember which. Very positive it is the bracket though. The voltage reg could be the problem, but since it only occurs at idle under a full load, I would be mkore inclined to check the belt. If there is too much slack then the alternator would not be spinning fast enough to produce the power.
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Old 09-30-2004, 11:52 AM   #3 (permalink)
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very well could be the voltage regualtor.. the alternator would have caused almost the same thing as the dead battery did. the abs light would come on, the battery light, and the car would start to die when in idle or even driving.

you can replace the alternator with a bosch they are the same fit and look. the valeo is a french alternator and they are ok, but in my opinion id rather a bosch.
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Old 09-30-2004, 02:53 PM   #4 (permalink)
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I just checked the alternator and the battery. The battery measurement was 12.5 volts, so it's ok. With the engine idling and no accessories turned on, the alternator was putting out 12.8 volts right after starting the engine. I then accelerated the engine a little, turned the AC, stereo and lights on and the reading went up to 13.6 volts at idle speed. At 2500 rpms, with all accessories on, the alternator put out 13.8 / 13.9 volts. I switched off all accessories and the alternator was still putting out 13.5 volts at idle speed.
What do you think?
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Old 09-30-2004, 08:35 PM   #5 (permalink)
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Alternators simply do not produce their rated output untill they reach a certain RPM, and it's certainly not idle speed.

I'm betting your voltage regulator is a bit messed up since a loose belt would most likely wear out really quickly and or make a lot of noise.
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Old 10-01-2004, 09:41 AM   #6 (permalink)
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Originally posted by bitcore@Sep 30 2004, 07:35 PM
Alternators simply do not produce their rated output untill they reach a certain RPM, and it's certainly not idle speed.

I'm betting your voltage regulator is a bit messed up since a loose belt would most likely wear out really quickly and or make a lot of noise.
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The belt doesn't make any noise. It seems fine. I guess it could be the voltage regulator. However, some body told me that when the VR is messed up, you can usually confirm this because the voltage could go up to 14.4 / 15 volts at some points. It didn't happen when I had the alternator checked. I' ll wait and see if the battery light goes on again. Maybe it was just a bad connection somewhere.
Thanks.
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Old 10-01-2004, 11:14 AM   #7 (permalink)
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my car runs anwhere between 13.5 and 14.1, usuallly always 14.1 i have a volt meter, and my car runs good, however i do have a high output alternator for my stereo system
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