Originally Posted by omodos

Hello, Ok been doing a bit of reading about using em, what is the official line on using these? Plug into the jump points under the hood while car off leave them 5mins and then trying starting, switch off and then disconnect booster? Or the cig lighter socket? Below are some pointers I read off the web, but would like to know what applies to the X5:

To protect ECUs etc, it is best if you connect the jump leads without either engines running. Leave the cables connected for about 5 mins or so before starting the disabled car. Leave it running for around the same 5 mins then switch it off. Disconnect the leads, and try to start it. If it still doesn't start, repeat the procedure. When it starts, do not rev it, but leave it idling for a while to charge the battery. This procedure will reduce the chances of a 'surge' which can cause ECU damage.

gti: Your comment: 'Never heard any thing about this not disconnecting while engine running ?'
It has been known for over 20yrs that disconnecting jump leads with engines running can cause 'spikes' on cars fitted with alternators. As far as I am aware, the first to suffer from this were the service light computers that BMW fitted. I have seen the results of it on a variety of makes and models over the years, so would always advocate doing it this way.