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E36 /7 Z3 (1996-2002)
E36/7 Z3 roadster and coupe talk with our gurus here.

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  #1  
Old 05-12-2010, 02:26 PM
booksix booksix is offline
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Mein Auto: 2000 Black Z3 Roadster
2000 Z3: Strange elctrical issues!

2000 Z3 Roadster, 2.5: Ok, so first off, for the last several months the car's battery would drain/die if the car wasn't driven for 4 or 5 days. It seemed to be getting slightly worse and eventually didn't charge so I replaced it with a brand new battery (it was the original battery) when I pulled it out of storage.

All seemed fine with the new battery until I took the car out for a drive; about 40 minutes. At around the 25 minute mark the radio started cutting out for 1 or 2 seconds at a time, spaced out over about 2 min intervals; then the gauges started randomly sweeping (not quite a full sweep to max though) accompanied by all the idiot lights lighting up, however the car never died. The car made it home without cutting out or anything but then it sat for about 2 hours and no longer had enough juice to even operate the door locks! Totally drained!

I figured the alternator wasn't charging and maybe was causing the drain. So I pulled it and had it tested at Checker and it passed all three tests. One thing to note: there was a green jumper wire coming off the 3 pin plug that connected the machine to the alternator plug. According to the on-screen diagram this jumper wire was to be connected back to the alternator near or possibly at the BATT connection. I was thinking maybe this was the exciter voltage that didn't get connected but why would the computer give a PASS if the field was never excited... I don't know the answer so I wanted to give these extra details. Any ideas as to what I should do next?
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  #2  
Old 05-12-2010, 03:49 PM
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EOD Guy EOD Guy is offline
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start it, unhook the neg cable, if it dies it's the alt
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  #3  
Old 05-12-2010, 04:01 PM
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dwm dwm is offline
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Symptoms sound like a loose battery cable connection. You sure the battery was drained? Did you check it at the battery terminals when the door locks didn't work?

When the battery cable disconnects with the alternator running, you get load dump. I haven't tested it in the roadster, but in most of my other cars, it would cause several things to reset.
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Old 05-12-2010, 04:23 PM
booksix booksix is offline
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Quote:
Originally Posted by dwm View Post
Symptoms sound like a loose battery cable connection. You sure the battery was drained? Did you check it at the battery terminals when the door locks didn't work?

When the battery cable disconnects with the alternator running, you get load dump. I haven't tested it in the roadster, but in most of my other cars, it would cause several things to reset.
Connections should be solid (it'd be crazy if it was a bad connection 4-5 times with 2 different batteries) but I'll double check!. What do you mean load dump? What am I looking for?

Also, I'm a bit concerned because I've always heard this is a bad practice as the battery acts as a buffer or safety against spikes getting to the ecu, etc...

Last edited by booksix; 05-12-2010 at 05:06 PM.
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Old 05-12-2010, 09:07 PM
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EOD Guy EOD Guy is offline
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All you are doing is disconnecting the neg terminal of the battery, it either dies or it doesn't. If it doesn't die hook the neg cable back up....... I have done this many times though out the years to verify if the alt is producing, the entire process takes about 3-5 sec.
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Old 05-12-2010, 10:14 PM
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dwm dwm is offline
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Quote:
Originally Posted by EOD Guy View Post
All you are doing is disconnecting the neg terminal of the battery, it either dies or it doesn't. If it doesn't die hook the neg cable back up....... I have done this many times though out the years to verify if the alt is producing, the entire process takes about 3-5 sec.
This isn't a good idea in general, and not one I'd recommend. While most modern OEM components have TVS to prevent damage from load dump, aftermarket parts (audio gear, radar detectors, GPS, etc.) may or may not have them.
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Old 05-12-2010, 10:20 PM
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dwm dwm is offline
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Quote:
Originally Posted by booksix View Post
Connections should be solid (it'd be crazy if it was a bad connection 4-5 times with 2 different batteries) but I'll double check!. What do you mean load dump? What am I looking for?

Also, I'm a bit concerned because I've always heard this is a bad practice as the battery acts as a buffer or safety against spikes getting to the ecu, etc...
You're roughly correct. I'm too tired to explain load dump in layman's terms, see the wikipedia page.

If the battery really is being drained, you need to chase down what's drawing all the current. If it's doing it with the engine off, put a 10 or 20A ammeter (one with a fuse) in series with the batttery and start removing fuses until you see a dramatic drop in current.
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Old 05-13-2010, 03:26 AM
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EOD Guy EOD Guy is offline
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I understand load dump theory....... IMO you may be doing more damage by allowing the strain on the electrical system to be repeated with an intermittant alt. I have used this for years and have had zero damage cause by it.

Last edited by EOD Guy; 05-13-2010 at 03:34 AM.
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  #9  
Old 05-13-2010, 08:11 AM
Z3SteveJ Z3SteveJ is offline
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Mein Auto: 2002 Z3 2.5
The new battery may be bad. The weird symptoms started when you changed the battery. I've had a battery with an intermittent bad internal connection, and another with an internal short.
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