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E36/7 Z3 (1996-2002)
E36/7 Z3 Roadster, Z3 coupe, Z3 M Roadster and Z3 M Coupe talk with our gurus here.

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  #1  
Old 05-08-2011, 11:37 AM
Fred Parmenter Fred Parmenter is offline
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Location: Medfield, MA
 
Join Date: Feb 2011
Posts: 34
Mein Auto: Z3 Black 2.8 2000 Roadstr
Z3 Battery Charge Sometimes Runs Down

Three times since I bought my 2000 Z3 2.8 Roadster in the last six months the battery charge has run down too low to start the car. Interior lights and dashboard come on, but there wasn't enough juice in the battery to start the car. The first couple of times I thought I might have left a door ajar or the trunk lid not fully closed.

A couple of weeks ago I went away for ten days, came back, and the car started right up. Two days later it wouldn't start.

My mechanic said he has a clamp type ammeter and detected no significant current draw when the car is off. (By the way, I didn't know there were clamp type ammeters for small currents like under an amp or so.) He said the battery and charging systems checked out fine.

My wife and I are are off next weekend on our first trip in the Z3. I'd hate for this happen on our trip. Any ideas?
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  #2  
Old 05-09-2011, 09:44 AM
KBH22102 KBH22102 is offline
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Location: Mclean, VA
 
Join Date: Oct 2007
Posts: 478
Mein Auto: 1997 Z3 2.8, 2002 M Coupe
If your alternator is good, then you must have a drain somewhere. My best guess is that it is still related to the trunk light. The wiring harness around the driver's side trunk hinge can become frayed over time and cause a short. Unless you load and unload your trunk often after dark, consider just pulling the light bulb in there
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  #3  
Old 05-09-2011, 11:33 AM
Mikey48 Mikey48 is online now
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Location: Charleston,S.C.
 
Join Date: Mar 2011
Posts: 420
Mein Auto: BMW Z4 3.0
How old is your battery. When my 2004 Z4 3.0i did this I replaced my battery and the issue went away. A quick test you can do to test your alternator is this. Start your car. Keep it running, while car is running loosen the positive cable on your battery. While car is still running remove the positive cable from the battery. If your car shuts off when you remove the positive cable from battery you need an alternator. If it keeps running it more than likely needs a new battery. Good luck !
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Old 05-10-2011, 11:29 AM
Fred Parmenter Fred Parmenter is offline
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Location: Medfield, MA
 
Join Date: Feb 2011
Posts: 34
Mein Auto: Z3 Black 2.8 2000 Roadstr
Battery Age

I bought the car used, so I don't know the battery age for sure. I'd guess 2 to 3 years because it looks so new. My mechanic did say, however, that the battery checked out fine.
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  #5  
Old 05-10-2011, 11:48 AM
Fred Parmenter Fred Parmenter is offline
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Location: Medfield, MA
 
Join Date: Feb 2011
Posts: 34
Mein Auto: Z3 Black 2.8 2000 Roadstr
Testing Current Draw

I wanted to test current draw in my car myself, instead of trusting my mechanic who said there was no draw on the battery when the car was off. Here's waht I did.

I opened the trunk and connected a wire between the chassis and the negative post of the battery. Call the my "ground jumper." This "ground jumper" is not necessary for the test below. I used it so I wouldn't have to reenter my radio code for what I did next.

Then I disconnected the wire going from the battery to the chassis by removing the nut which connects it to the chassis. I did not touch the end which attaches to the battery. Then I connected the end of the cable just loosened to the negative lead of a multimeter and connected the positive lead of the multimeter to the chassis. I turned the multimeter on, set the function to ammeter, and the scale to 20A. I then disconnected "ground jumper."

The multimeter read 0.67A as the trunk light was on. I removed the trunk light the multimeter read 0.00A. That proved to me that neither the radio nor anything was else was on. Of course since I was using the 20A scale I guess there could still have been as much as .005A, or 5MA.

Even though it wasn't necessary I decide to some other tests while I had everything hooked up. The trunk was left out. Here are the results.

Opened driver door - multimeter read 0.52A.
Turned on ignition and radio (driver door closed) - multimeter read 1.72A.
Turned on ignition (radio off, driver door closed) - multimeter read 1.18A.
Opened driver door, pulled key out, and closed door - multimeter returned to 0.00A, however this took about a minute. It first read 0.57A (while the interior light was on) and then wen to 0.03A, 0.02A, 0.17A, 0.06A, 0.04A, back up 0.15A, and then finally 0.00A.

Even though everything checked out fine, I have taken the advice offered earlier of playing it save and leaving the trunk light disconnected.
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