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.