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Need The Experts-mysterious Electrical Problem???

2K views 6 replies 5 participants last post by  JonnyM3 
#1 ·
Hi everyone, Im new to this forum, the name is Jon and I am a recent buyer of a 97 Dakar yellow M3 with 48k on her.

I am pretty knowledgeble about M3s (for the most part e36), but this problem has me stumped, especially since im not the best electrical guy.

So for all you electrical junkies heres my issue:

When the guy sold me the car he said it was in perfect order, and for the most part it was. But about a week after I started talking to him he said the car wouldnt start. So he said he took it to BMW and they replaced the battery and checked altenator and hooked it up to a computer to do a draw test and they couldnt find a thing wrong with it. They gave it back to him and in a nut shell said "your on your own".

So I took the car to Intersort in Mclean VA to see if they could find out what the issue was, by the way I would never take my car back there again they will rip you off and DO NOT stand behind there work (at least with me). Anway they said it was the battery and there was nothing wrong with the car just needed a new battery. The guy who sold it to me was straight honest, he said look, thats not it the car has an electrical issue, BMW said they couldnt find it. So he knocked some $$$ off the price and I was on my way.

So I buy the car and yes 3 weeks later I dont drive it for about 4 days and its dead......completley dead!!!

So long story and now heres where you guys can help please:

1.The car makes a whine like the altenator is going, so this could be it but not likely since bmw said no to that. But still possibility.

2. I did a bad thing :banghead I have been jumping it from the battery instead of from the front + terminal like you should. I dont know if this has screwed up my voltage regulator and now the car is drawing to much or what. And my OBC is giving me a BRAKE LIGHT CIRUIT-CHECK OWNERS MANUAL. This only comes on sometimes which is weird and is giving me a LICENCE PLATE BULB FAILURE. Which is weird to cause I just replaced the bulb so maybe im frying things by jumping it from the battery :banghead So what are the problems that jumping from the back can cause is basically what im asking.

3. And lastly my car idles low like right at 500.. maybe not putting out enough electricity??? altenator???

So any info about any experiences or anything you guys could think of would be much appreciated.. The car sits there now after one day and is dead... So maybe I shorted something out by the way i jumped it and maybe the previous owner did that to... if that is it how do i find the short or do i need to replace the ecu or one of the control units. I dunno Im stumped but thanks for any info and thanks for listening to my story.

I gotta figure this out cause Im in college and have no more money to put into her.

Thanks again in advance... Jon
 
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#2 ·
I hope it is ok to jump the car from the battery. I have had to do that to my car about 3x. But so far no damage at all to her. I hope this helps. But if any one knows for sure if it causes damage, I would like to know, so I can make sure nothing was damaged.
 
#5 ·
First you need to get a battery charger and charge up the battery. If the battery is in fact new and it goes dead and is left dead, the battery can get ruined.
Next you can check if that batttery can in fact hold a charge. It's rare but possible that the new battery is no good. If you aren't going to use the car for a few days and you have the battery fully charged, measure the voltage between the + and - terminals to make sure its about 12.3 volts. Next disconnect the battery terminals and leave them off for several days. Then measure the voltage between the terminals and it should be the same as when you left it. If it's the same the battery is good. If significantly lower the batttery is bad.
Next connect an ammeter between the + battery post and the + wire and read the amps.(Turn off the trunk light) There should be a little draw, (under .5 amps) for the clock etc. If there is a large draw, something is shorted or is turned on. Start pulling fuses. When the current draw drops you have found the bad circuit and can look further in that area.
Also with the car running the voltage should be 13-14 volts between the +- battery terminals. If so the alternator and voltage regulator are probably ok.
Jumping from the vattery is ok for the car. It just doesn't provide the max voltage for starting because of the loss through the bat wires.
This should give you a place to start.
 
#6 ·
Hi Jon, i'm not sure if this would help but im just trying. I think it should be the alternator or you should check with the buyer, if it was damaged anywhere before. IE i have a lexus es300 and it was damaged on the door, it did not seem any big deal, turned out that my my door wasnt really closed tight even it looked like it, which caused my battery to go dead in a light. And do not keep charging with the battery, it will eventually mess up your car.

Hope this will help,
BmwNoobie
 
#7 ·
Originally posted by BmWNoobie@Dec 6 2004, 03:03 PM
Hi Jon, i'm not sure if this would help but im just trying. I think it should be the alternator or you should check with the buyer, if it was damaged anywhere before. IE i have a lexus es300 and it was damaged on the door, it did not seem any big deal, turned out that my my door wasnt really closed tight even it looked like it, which caused my battery to go dead in a light. And do not keep charging with the battery, it will eventually mess up your car.

Hope this will help,
BmwNoobie
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Thanks a lot for the help guys. Keep posting if anyone knows anything or has any other ideas. Im going to try all of them!! :lol: Thanks and Ill let you guys know, I go back this weekend for winter break and Im going to start as soon as I get home. But I like I said any more ideas, just post!
 
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