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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 3 Series / 4 Series > E30 (1982 - 1993)

E30 (1982 - 1993)
God's Chariot. The E30 was produced primarily from 1982 through 1991. The cabriolet was the one exception which was produced through 1993.

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  #1  
Old 05-26-2011, 01:39 PM
Woody325 Woody325 is offline
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Reversed polarity on battery - I am a dolt

Hello all,

What better way to show what a complete idiot I am than to ask for help for something quite embarrassing ... coming from an electrical engineer.

I somehow managed to reverse the polarity on the battery when I charged it. You'd think the sparking while connecting to the terminals would have made me think something was wrong, but knowing the terminals are sized to go on only one way I plowed ahead because "I couldn't be doing it wrong". I had the battery connected for about 20 seconds or so while my brain processed the smoke coming from the alternator. Duh.

So now after rigging up a temporary connection with a set of jumpers I have working lights, wipers, radio, etc, but the car won't crank. I also have the battery light on regardless if the ignition switch is on or not.

I can guess the alternator is fried - the smoke gave it away, but it should still turn over if that's the only thing wrong with it. I checked all of the fuses, and none are blown.

I've searched and found similar issues, but not exactly the same symptoms ... so I'm reaching out to the forum for help. Any help would be greatly appreciated.

Thanks in advance.

Last edited by Woody325; 05-26-2011 at 01:40 PM.
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  #2  
Old 05-26-2011, 02:42 PM
SCE30318i SCE30318i is offline
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Coming from a computer tech POV you more than like fried some valuable components in the system :/

Good luck bro
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  #3  
Old 05-26-2011, 03:38 PM
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downhiller downhiller is offline
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have you tried jumpin the starter at the solenoid? just touch the smaller terminals with a wrench, should try and start. if not, starter is fried
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  #4  
Old 05-26-2011, 04:39 PM
Woody325 Woody325 is offline
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Okay so here's an update ...

Went out and did what I should have done after waking her up after three years, which is that I bought a new battery (Bosch, ouch).

Put the battery in and she now cranks, but will not start.

Still get the battery light on whether key is in or not, but also noticed I get the Anti-Lock light on when it's cranking.

So I can guess the alternator is toast, and will be replacing it ASAP.

Also suspect the fuel relay might have gotten fried (?) ... just a guess, so for $8 worth a try.

Any ideas?

Last edited by Woody325; 05-26-2011 at 05:12 PM.
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  #5  
Old 05-26-2011, 06:07 PM
SCE30318i SCE30318i is offline
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woody325, i did a little bit of searching on google and came across this. apparently this one guy came out from lunch one day and noticed his battery light was on in his car. turned out there was a bad diode on the alternator. i'm assuming that this could also be true on yours since you saw smoke coming out of it. have you tried completely disconnecting the alternator and trying to start it?

here's what his post said..
Quote:
A buddy of mine has a voltage meter, and found an ignition wire that was still getting current even when the car was off. According to my Bentley manual, this can be one of two things:
1.) A diode in the alternator is blown. (A diode is pretty much like a one way valve, and if it goes bad, current continues to flow freely to wherever it was previously regulated to send power to.)
2.) A bad wire. (Since the wire is still getting current, it's obviously not bad.)
I then talked to a BMW mechanic I've taken my car to before, and he explained that a diode is pretty much like a one-way valve to a designated place, and when it went bad, it pretty much opened a trickle of power coming directly from the battery to the ignition. It's small enough that it could take up to a couple days to drain the battery, and the alternator still recharges the battery when the car is on, so that's why it acted so strangely.
also here's a link to the post.
http://www.dtmpower.net/forum/e30-3-...n-car-off.html
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  #6  
Old 05-26-2011, 07:20 PM
Woody325 Woody325 is offline
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Thanks for the input SCE. I'm sure some of the smoke coming from the alternator was also from the poor little diodes screaming. There is no doubt the alternator is toast. I could be wrong but I don't believe the alternator is what's keeping it from starting.

I'm not hearing the fuel pump kick on when I turn the key so that's why I'm guessing the fuel relay ... But then again I'm pretty-much guessing.

This really sucks because after close to $1200 in parts and weeks of off-hours work on everything from intake gaskets to timing belts I was just seconds away from being done. Now I'm looking at least at another $350 and who knows how much time to trouble shoot ... And I'm really hoping I didn't fry anything else like the ECU.

Last edited by Woody325; 05-26-2011 at 08:29 PM.
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  #7  
Old 05-26-2011, 08:14 PM
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downhiller downhiller is offline
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the fuel pump only comes on when you start cranking the starter. its not like a normal american or jap crap fuel pump.
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  #8  
Old 05-27-2011, 01:39 AM
Billwill Billwill is offline
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Quote:
Originally Posted by Woody325 View Post
Thanks for the input SCE. I'm sure some of the smoke coming from the alternator was also from the poor little diodes screaming. There is no doubt the alternator is toast. I could be wrong but I don't believe the alternator is what's keeping it from starting.

I'm not hearing the fuel pump kick on when I turn the key so that's why I'm guessing the fuel relay ... But then again I'm pretty-much guessing.

This really sucks because after close to $1200 in parts and weeks of off-hours work on everything from intake gaskets to timing belts I was just seconds away from being done. Now I'm looking at least at another $350 and who knows how much time to trouble shoot ... And I'm really hoping I didn't fry anything else like the ECU.
As downhiller states above...the fuel relay only comes on once the motor starts cranking!

I would be very suprised if you have NOT fried your ECU Try and borrow one but I personaly would not trust putting my good ECU into your car as something could damage it.....try the breker yards for a used ECU
There is also a diode in parrallel to the aircon clutch...to cover back EMF...try disconnect your aircon clutch for a while. Some of the relays are so called Solid State as they have some built in diodes, transistors etc. that then activate the relay...these relays could be toast as well!
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  #9  
Old 05-27-2011, 05:34 AM
Woody325 Woody325 is offline
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Well then ... someone needs to inform the guys at Bav Auto that the relay doesn't come on until the motor cranks.

I'm hoping I didn't fry the ECU as well, but at this point it would seem that we're both just guessing. In searching around I see there are several threads out there with similar boneheaded mistakes, but unfortunately they all seem to have different outcomes, and a fried ECU isn't a definite result. At this point I almost wish it was (!) so that I could fix it and be done with it ...

Thanks for the input.
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  #10  
Old 05-27-2011, 06:03 AM
7pilot 7pilot is offline
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In an unmolested car, there is a thinner gauge wire with a fusible link, running with the battery cable towards the front of the car.
This wire powers the ECU memory.
If the wiring is intact, then the fuse is blown and hopefully your Ecu has not been damaged. I would not hold my breath though. 20 secs of reverse polarity can destroy the 20+ yo wiring harness.

m
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  #11  
Old 05-27-2011, 06:27 AM
Woody325 Woody325 is offline
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Yeah, I checked that out. The wiring looks to be intact, but I couldn't verify if the fuse-able part was blown or not. It doesn't 'appear' to be. I cut open the outer shrink cover covering both cables, and visually inspected as well as I could without cutting open the actual fuse-able link portion. I didn't cut into the fuse-able portion to check it out because I was getting power in the engine bay, and figured that it was not the issue.

So how would I know it's toast? No other way but to slice it open?
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  #12  
Old 05-27-2011, 08:36 AM
Woody325 Woody325 is offline
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alrighty then ... so I sliced open the fuse-able link, and see that it's full of alumininum oxide residue. It's definitely broken now, but I'm not sure if that was a result of me cutting it open, or if in fact it was broken during the reverse polarity. It doesn't appear to be melted or burned though, which I would expect if it had blown under electrical duress.

Question - do I need to replace the exact part, or is there an alternative quick replacement part? Are these universal?
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  #13  
Old 05-27-2011, 09:25 AM
Razorthirty Razorthirty is offline
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Quote:
Originally Posted by Woody325 View Post
Well then ... someone needs to inform the guys at Bav Auto that the relay doesn't come on until the motor cranks.

I'm hoping I didn't fry the ECU as well, but at this point it would seem that we're both just guessing. In searching around I see there are several threads out there with similar boneheaded mistakes, but unfortunately they all seem to have different outcomes, and a fried ECU isn't a definite result. At this point I almost wish it was (!) so that I could fix it and be done with it ...

Thanks for the input.

I'm no electrical genius but when i did that years ago i just sniffed around with my nose and smelled out the fried electricals, try putting your sniffer on the ECU that might give you a little insight there.
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  #14  
Old 05-27-2011, 09:56 AM
Woody325 Woody325 is offline
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Yup - already did the sniffer test. It was a little difficult though because of the powerful smell from the alternator ... couldn't tell what else was burned up, and had the smell in my nose well into the evening. Haven't gotten to the ECU yet though - that'll be the first thing I 'sniff out' when I get back to it.

Thanks,
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  #15  
Old 05-27-2011, 10:42 AM
Woody325 Woody325 is offline
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SUCCESS! Perhaps only partial, but I'll take it!

So I jumpered the fusible link from the battery and tried again - and it started! I am sooo friggin lucky (so far anyway).

I still have the alternator light on, which is understandable, but I'm also getting the oil light - not sure what that's all about. I didn't want to run down the battery so I guess I'll have to wait to troubleshoot that until I get my new alternator.

I would assume that the fact it fired up means that I'm out of the woods from a bad ECU, ABS relay, main relay ... would the collective agree?

Thanks.
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  #16  
Old 05-27-2011, 03:44 PM
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downhiller downhiller is offline
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if it runs then yes you should be in the clear now. but to replace the fuseable link, you can throw in a 5amp or whatever it was rated at normal fuse or cartridge fuse. i say cartridge because you can heat shrink it and make it more water tight
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Old 05-28-2011, 05:30 PM
SCE30318i SCE30318i is offline
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Good work man! ... Next time pay more attention haha
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  #18  
Old 11-22-2012, 04:07 AM
nmebadboy nmebadboy is offline
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Hi, a family member of mine has done exactly the same thing! Doh! Can you confirm the fuseable link is an orange thing with a pair of thin wires going to it? Located in the battery compartment? Many thanks.
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