Using jump leads...
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Category: Technical & Model Specific Forums
Forum Name: General Motors
Forum Discription: This forum will deal with technical issues for the cars not dealt with in the other forums. These don't need to be BMWs!
URL: http://www.bavarian-board.co.uk/forum_posts.asp?TID=3046
Printed Date: 22-May-2024 at 12:40
Topic: Using jump leads...
Posted By: j_p_buckley
Subject: Using jump leads...
Date Posted: 18-August-2003 at 12:02
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Hi ya!
I had to put my BMW in a garage for storage for a few months, I went to get it out for quick clean and a polish over the weekend, the battery had gone dead! 
I have a set of jump leads, I thought this might happen! however on the instructions there was a note saying don't use jump leads on cars that have on board computers??? Why is this?? I left it alone, hopin you guys might be able to help! Im not to confident with cars at the best of time's and didn't want to do any damage! Any ideas?? |
Replies:
Posted By: lancelotII
Date Posted: 18-August-2003 at 16:32
| Used them many a time on my car which has an on board computer, without problem. They also say connect the earth to a body part rather than neg. of the battery. That just doesn't work so did it the old fashioned way neg to neg and pos to pos and the car started no problem, no damage. Lets face it, if the on board kit is that fragile then it's been designed by monkeys. |
Posted By: j_p_buckley
Date Posted: 18-August-2003 at 16:59
Cheers for the response!! Ill give it ago!
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Posted By: Eamo
Date Posted: 18-August-2003 at 17:25
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I think i read something about this as well. What happens is that a power spike/surge gets sent to the ecu (i think) when you use the leads and it gets fried.
It doesnt matter how good its designs are as even the best computers can get fried if they get a power spike/surge. However, I do stand to be corrected on this. ------------- |
Posted By: Kevin_E30_318iS
Date Posted: 18-August-2003 at 21:57
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To be on the safe side, why don't you remove the battery and put it on a trickle charger? If the battery is totally flat, the alternator in the car won't re-charge it fully.
The reason for connecting the negative cable to the chassis rather than the negative terminal on the battery is to avoid the possibility of the battery bursting. Well, thats what I read in a manual somewhere! ------------- Kevin_1990_318iS |
Posted By: lancelotII
Date Posted: 19-August-2003 at 00:03
| Ask yourselves this....hypothetical scenario. Your racing a group N e30 M3, you come in for a pit stop and the battery is flat, what do you do ???? Get it on a trickle charger.....disconnet the ecu .......no you get the booster pack from the garage and wack it on, start the car and away. I know you can fry ecu's and all that crap, but seriously if it was that bloody flakey these cars would all be on bricks now......... |
Posted By: Nick
Date Posted: 19-August-2003 at 08:21
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I never dared to 'boost' start the M3 because of the fear of frying the ECU..
.. which was frustrating considering the many times that it went dead and I had a very handy sloping gradient to roll down. .. instead, I used another battery with jump leads attached to the dead one.. it worked fine every time. Nick |
Posted By: b318isp
Date Posted: 19-August-2003 at 10:04
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Make sure the doner car has its engine running when you make the connection.
The negative is not attached to the battery to prevent it sparking beside the Hydrogen vapours given off by the battery! 
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Posted By: j_p_buckley
Date Posted: 19-August-2003 at 10:48
Maybe I should ave just disconnected the battery first!! Im going to call bmw and make sure! Ill let you know what they say! Cheers!
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Posted By: j_p_buckley
Date Posted: 22-August-2003 at 09:14
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Hi all!!
Right I've got my battery re-charged, local garage sorted it out for me! Just one more question... when you put the battery back in do you have to connect the positive or negative first? Anythink I need to be aware of? I don't really want to be Electrocuted!!!
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Posted By: b318isp
Date Posted: 22-August-2003 at 10:19
| Attach the negative last (and disconnect it first). |
Posted By: PhilC
Date Posted: 22-August-2003 at 14:44
| I jump started my second car, an Opel Zafira, after a flat battery. After that it did not start too well until one day it just died. The ECU s**t itself and I think the damage was done when trying to jump start. New ECU £600+ ouch. |
Posted By: paul320i
Date Posted: 27-August-2003 at 18:37
| I was told if i really need to jump start the car, to turn on all lights and but blowers on full first, not sure how this helps but only to be done is desperate. |