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I'm having a problem with my '93 500 SEL. Here are the symptoms-

1. Alternator light comes on occasionally on start up. If I turn the car off and then restart it goes away.

2. After starting the car after work and going home, the car will crank slowly when I start it to put it in the garage. It starts but slow.

3. Last weekend we had to run some errands and I waited in the car with the "rest' function on the climate control for about 15 minutes. When my friend got back the car would not start. Turned over very slowly and then made the machine gun RAT TAT TAT TAT sound from under the hood. Jumped the car and it started right up.

4. Took the car to Autozone where I had the battery and alternator tested and was told they were ok but the battery wasn't fully charged. (I'd driven the car for about a half an hour).

5. Yesterday noticed that the car started slowly and while going through the drive through I noticed that the odometer and trip odometer and radio backlighting were flashing off and on.



The battery and the alternator are both 4 years old but like I said the guy at autozone said they were ok.

Oh yeah, and just as an aside my indy has decided to close up shop so I feel helpless!
 

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Discussion Starter #3
I don't know. I'm not really an electronics guy (yeah, probably should have stuck with my 300SD).

All I know is that the guy at autozon tested the battery with the engine on and with it off and said the charging system was ok and that the battery was ok
 

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I would say from reading your post that the alternator is not OK and you need a new brush pack. You can buy a multimeter on Ebay for $8 that is good enough for this.

When the car is running there should be about 14volts across the battery, so simple to use a meter, just select the 20volt DC range
 

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I have seen batteries do strange things, they can have problems that magically disappear when put under a load test. Also the alternator can put out enough power to be barely in the green. Ground issues can also be a factor. If you have a multimeter. Just read the voltage at the battery. It should be around 12.4 off and up to 14.1-14.6 running. This can vary. But the car uses lots of power for all of those computers
 

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I have seen batteries do strange things, they can have problems that magically disappear when put under a load test. Also the alternator can put out enough power to be barely in the green. Ground issues can also be a factor. If you have a multimeter. Just read the voltage at the battery. It should be around 12.4 off and up to 14.1-14.6 running. This can vary. But the car uses of of power for all of those computers
Sure a battery can get a dud cell that goes high resistance, the start of any cold weather shows the fault up often, drive the car for ½ hour and all fine till the next day starting
 

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Battery 4 years old is a good start....just because autozkne people say its OK does not mean it is.

Here in Vegas.....battery hits 3 years old just replace it.don't even wait.
 

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My bet is on the battery. I had the parts store test my batter when I had symptoms of slow start in the mornings, sometimes the battery light came on for a few seconds after start up. The battery tested out okay as well as alternator. My battery was 5 years old at the time. I changed the battery and issue was fixed.
 

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Discussion Starter #9
I replaced the battery this morning. Guy at autozone said that the battery tested fine but was down from the level it should be. He then tested the alternator (car barely started) and said the alternator was well within specs, so I wenrt ahead and replaced the battery. Car starts fine now and even some features (like defrost) that didn't work before work now......STRANGE cars!


Thanks for all your help!!!!
 

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those are all classic battery symptoms. If autozone is your best bet to look after your W140 then its reeaally time to find a good mechanic


our W140 is not as sensitive with low battery charge or jump starts. if you had an E38 or E39 BMW you could've fried your transmission ECU by now...
 

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haha.. was just about to say "replace the battery" but you already did! Problem should be completely solved now
 

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Discussion Starter #12
our W140 is not as sensitive with low battery charge or jump starts. if you had an E38 or E39 BMW you could've fried your transmission ECU by now...[/QUOTE]



One of the many reasons I don't drive BMW's anymore
 

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Your problem is not solved, you have a charging issue. It could be a bad connection from the alternator, but most likely the alternator itself. If you dont want to be stranded somewhere, have it professionally fixed.
 
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