GreyE34 0 Report post Posted February 29, 2008 My battery is flat because I left the boot lid slightly open over night. Now I want to start the car with the help of a mate's car and a set of jumper leads. Am I at risk of frying the electronics, and does anybody have any handy hints on how to avoid this? Thanks in advance for any helpful suggestions. Quote Share this post Link to post Share on other sites
Guest Simon* Report post Posted February 29, 2008 (edited) If, like it seems, you have an E34 there should be a jumper point under the bonnet on the back of the block nearest the firewall - may have a plastic cover to unclip but will be marked as a terminal. Attach appropriate jumper here (can't remember which flavour but it's marked) and earth the other terminal to something substantial. Rev the other car, cross fingers, turn ignition and hey presto! I've done it, it's worked for me and I haven't fried anything - the owner's manual even recommends you do it like this Good luck! Disclaimer: If you fry your electrics it had nothing to do with Simon. Print out and sign below SIGNED: ______________________ DATE: ___/___/2008 Edited February 29, 2008 by Simon* Quote Share this post Link to post Share on other sites
Foohey 0 Report post Posted February 29, 2008 jump started my car every day for a week till i got my new batt... (E36) and all is good. but i was told to be careful cos things can go weird, like my mates drivers airbag blew up in his face (not sure if it was a because of the jumpstart but he got bad whiplash non the less ) Quote Share this post Link to post Share on other sites
bravo 35 Report post Posted February 29, 2008 The ecu is the bit you need to worry about. Also it is a spike that causes the most damage (Like that which can happen when you connect the other vehicle to yours or you start the other vehicle. As the ecu is not connected to the power circuit with the ignition off, the best bet is to leave the ignition off, start the other car, connect the leads, then start the flat car. Most modern leads have spike protectors. Even so I tend to use a jump-start kit which has electronic protection. Quote Share this post Link to post Share on other sites
mr E34 11 Report post Posted February 29, 2008 (edited) The ecu is the bit you need to worry about. Also it is a spike that causes the most damage (Like that which can happen when you connect the other vehicle to yours or you start the other vehicle. As the ecu is not connected to the power circuit with the ignition off, the best bet is to leave the ignition off, start the other car, connect the leads, then start the flat car. Most modern leads have spike protectors. Even so I tend to use a jump-start kit which has electronic protection. Definitely correct. Also when you get your car started turn on BOTH CARS LIGHTS to load up the system and then disconnect the jumper leads. Don't forget the ECU does still have a main +12v even with ignition off. Edited February 29, 2008 by mr E34 Quote Share this post Link to post Share on other sites
GreyE34 0 Report post Posted February 29, 2008 Thanks guys for all the hints. Will give it a go tonight and hopefully be mobile again. Quote Share this post Link to post Share on other sites
Neal 544 Report post Posted February 29, 2008 The ecu is the bit you need to worry about. Also it is a spike that causes the most damage (Like that which can happen when you connect the other vehicle to yours or you start the other vehicle. As the ecu is not connected to the power circuit with the ignition off, the best bet is to leave the ignition off, start the other car, connect the leads, then start the flat car. Most modern leads have spike protectors. Even so I tend to use a jump-start kit which has electronic protection. You also have to look out for ICE gear as well. I jumpstarted a car that had broken down in the middle of no where so couldn't really leave them stranded. Was careful and connected to earthing points on the body , then the two positive terminals of on the battery. All seemed ok They drove off happy. I'd left my stereo on whilst doing this. Drove off, noticed a lack of Bass , the Alpine Subwoofer Amp ended up having it's PSU fried. Quote Share this post Link to post Share on other sites
bravo 35 Report post Posted March 1, 2008 You should actually connect the positive terminals first. If you connect the neg terminals, then touch the positive against anything metal on the car you will have a short. Quote Share this post Link to post Share on other sites
