Flickering lights - alternator problem? HELP

[280S]

Hi. I am a long time user of this forum. I have solved many problems in my vintage 280S, 1969 with info I was able to find here. I hope you can also help me with some issues I have with a 5 speed, 1993, BMW 318IS I recently bought (yes, I love German cars but I am new to BMW). From what I have seen, electrical system in the 318IS has some similarities with MB's.

My 318IS has only 27 K miles and I bought it from one of my partners 4 weeks ago. The car is like new and has been regularly serviced by a BMW dealer. When I bought the car, I noticed that instruments lights and headlights were flickering at idle. Flickering seems to increase as RPMs go up and then just disappears when the car is running.

A couple of days after I bought the car, it suddenly died on me. It was late and I was stuck in the traffic. Then, the headlights and instrument lights started to fade, ABS light went on, battery light also went 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 and the new battery checked. The battery measurement was 12.5 volts. With the engine idling and no accessories turned on, the alternator was putting out 12.8 volts right after starting the engine. I then turned the AC, stereo and headlights on and the reading went up to 13.6 volts (at idle). 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.

The car has been running fine for the last three weeks. However, last week I noticed that the instruments lights were slightly dimming and the battery light went on twice for a couple of seconds at idle. The battery light was dimming and then just turned off and everything went back to normal. Yesterday, the same happened again. Battery light went on at idle, with AC, headlights and stereo on and then just went off by itself.

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 (consider that the car is 11 years old but has only 27 k miles)?

3. I believe that the voltage regulator is attached to the alternator (my car came with a Valeo 105 amps alternator), so if I buy a new alternator I assume that I will not need a new voltage regulator, right? I am asking this question because my 1969 280S has a voltage regulator which is not attached to the Bosch alternator.

Your answers are greatly appreciated.

[mercedesdoc]

Altenator needs replacing

[nglitz]

Yeah, throw expensive parts at it.

Don't even think of hooking up a voltmeter you can read while you're driving and the problem occurs. Never do any real diagnosis. Don't ever consider a subassembly like a voltage regulator or brushes. Never check the diodes in the alternator. Don't even check the continuity of all the electrical connections in the charging circuit.

Just spend $ in big chunks.

[manny]

nglitz

You HAVE TO control that PMS !

[mercedesdoc]

Don't even think of hooking up a voltmeter you can read while you're driving and the problem occurs. Never do any real diagnosis. Don't ever consider a subassembly like a voltage regulator or brushes. Never check the diodes in the alternator. Don't even check the continuity of all the electrical connections in the charging circuit.

No why should I do any thinking, First off It is not my car. You sat there and wrote that long post. You clearly marked your problem for me. You can write more post and test more things out. But if it was in my shop for diag, it would have been in and out before you finished writting your post.
I estimate about 28 ro's a week. So all my customer cars are fixed and happy. EXpensive part???? BENZ!!!!

[G-Benz]

A healthy charging system puts out up to 14.4V at idle w/no accessories on. Your voltage regulator seems to be trying to do its job since it seems to be pushing a bit more juice to the system when to start switching on accessories. Still, I think 13.8V or so is a bit anemic with the engine running and no real load on the electrical system.

Despite the previous rants, I do agree that the alternator (or components within) are suspect. I have later MBs and the only cure is swapping out the entire component, but yours is early enough to have the seperate regulator and brushes that can be replaced w/o tossing out the whole unit...far cheaper of course.

And a sick charging system can bring an already-old battery to its ultimate demise...