Hey guys, i've been having this problem for almost a month now.

First off, i wanted to say that I have a Brand NEW BATTERY and a REBUILT alternator with new brushes, bearings and NEW voltage Regulator! Battery connections tight and cleaned. Alternator Belt looks new and in good condition and Tight!

Heres the problem:

Sometimes my car charges fine and sometimes it doesn't charge, why?
I know it doesn't charge because the battery light on my dash board flashes.

I also know it doesnt charge because just recently bought one of those Voltomenter that plugs into ur Ciggerate ligther have that 3 indicator light: red = under 12 volt, orange = ~12 volt, green = 13+ Volt

sometimes while driving in the freeway, it would just be red! and my battery light comes on, and dash board light is dimmed and then i drive it a little more then its green again and my battery light is off and so its charging again!

Just today, drove it to school with the battery light constantly on and flashing and voltomenter indicator light on RED (not charging)....when i get outa school, it's back to normal again.

I can't find any pattern of driving habbits that causes these, sometimes it happens while parked and idle, sometimes on freeway, sometimes on innner roads, sometimes with headlights on, sometimes with it off!


Same thing happened 2 weeks ago before i changed my battery and got my alternator rebuilt, after i did it, i thought i fixed it because the problem went away, until yesterday...why???

PLEASE HELP!
THnx guys

1997 2.8 Z3

Your rebuilt alternator could be bad, or there could be a poor connection in the charging path from the alternator to the electrical system. For now I'd tend to favor the latter as a cause since it seem to be an intermittant problem.

Thnx for the reply guys!

I've took the alternator out and tested it @ the shop already and it was fine. Even load tested it and its fine.

Now, it seem to work intermittedly in my car, so could it be that when i took it out and tested it for the 5 minutes, it worked at the time? is there any long term test or anything or will it make any difference?

I thought if it work for 5 minutes, it should work forever, isnt this right?

And about the loose ground connection, where should i check for those?

do u guys know where i can get access to a wiring diagram?

my car is a 1997 2.8 z

thnx for all ur help guys!

There's a ground cable between the engine and the frame. I don't know for sure, but it may be on the right side, with the engine terminal under an engine mount bracket bolt. It should be easily visible from under the car. The cable will have brown insulation on it.

The junction for the alternator cable is on the stud for the starter motor. Disconnect the battery ground, remove the cables from the starter, and sand the terminals until shiny.

Check to make sure all connections are clean and tight.

I don`t know if a Bentleys manual would have a wiring diagram that would detail the "excitation" circuit for the alternator.
Most cars pass current through the "Alternator" warning lamp on the dashboard to excite/engage the voltage regulator.
When you turn the ignition key, current flows from the battery, (obviously) through the ignition switch, then through the alternator warning lamp on the instrument cluster and then out to the voltage regulator on the alternator.
An interruption or intermittent connection anywhere along this path will remove the excitation signal to the voltage regulator, in effect turning the alternator off. The reason the car is wired this way is that it "proves" the circuit wiring from the ignition switch, through the warning lamp and out to the alternator by illuminating the lamp each time you start the car.
This is the "simple" voltage regulator excitation supply circuit utilized on most cars.

This explanation however does not support your symptom that the warning light illuminates on the instrument cluster and your "Volt-o-meter" confirms that you have lost your charging voltage since a failure of the simple circuitry would not allow the lamp to illuminate because the circuit would be open.
(Yes, all you electronic experts, I know there is a resistor in parallel with the lamp to preclude having a burnt out alternator warning lamp bulb cause a failure of the charging circuit).

BMW however has what is called an "Unloader" relay in the voltage regulator excitation supply circuitry.
Your model of BMW may use a relay in parallel to the alternator warning lamp circuitry.
This unloader relay will be in the circuit that "feeds" the excitation signal upon starting the car, to the alternator. A failure or intermittent contact within this relay will cause the symptom you are having and would support [all] of the diagnostic information supplied at this point.
Again, hopefully your Bentleys manual will detail this unloader relay circuitry as it does in mine.
andrew