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01-28-2011 08:59 PM #1
More charging system woe information (long)
Here again regarding my starting woes. I was going to update the original post, but for some reason it is closed to further posting. Here is my original post text:
"So, I have had hard starting for a few days, so I went to my local Autozone and the battery checked out okay. Checking the alternator, he said the output was fine, but his little checker said an internal diode was bad inside the alternator.
So I am guessing the voltage regulator is bad, and that it is inside the alternator. Do i just order a new alternator and replace the whole thing at once, or can the VR just be swapped out?
From my searches, it seems like the '97 is a simpler swapout than later years, does anyone have a web writeup on the procedure? One post said to expect about 1.5 to 2 hours for the job."
I got lots of suggestions about things to check. I have been 'bandaiding' the situation by taking a long drive once a week or so, which seemed to fully charge the battery and give me 4 or 5 days of pretty good starting.
I finally got around to buying a multimeter and did some of the suggested tests. Here is what I got:
When car is off, battery voltage after sitting overnite was 11.4 V. The 'battery test function' of the multitester said my battery was good.
I disconnected the negative lead and got a reading of .02mA. I think this indicates no significant battery load. I reconnected the battery and started her up.
I got a constant reading of charging between 13.9 and 14.1 DC volts. I think this is satisfactory. I shut her down, disconnected the battery again to measure load and again got .02mA. Does disconnecting the battery shut down all the loads that are supposed to be there for the 17 minutes? If so, how do you measure them?
Anyhow, if it is indeed a bad diode, I was told that this suggests that the same circuit that charges the battery when running allows discharging when the car is off. Do I have that right, and if so, how do you measure that?
I now have the cash to replace the alternator, but hate to pay the $225 without confirming as much as I can that it is the problem.
Sorry for the long post, thanks again for the help.
Michael1997 540i Automatic
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