The manual for my Mazda 323TD advises the following procedure for using jump leads:
Connect a lead from the positive terminal on the discharged battery to the positive terminal on the booster battery; then a lead from the negative terminal on the booster battery to the 'engine hanger' in the discharged car's engine bay.
My FiL followed this method to jump start his petrol Corsa C. As soon as he put the lead on the engine hanger of the Corsa it sparked. The car then started okay with the jump but it later transpired that the ECU was fried! It's possible that on trying to use a battery charger before jump starting he connected the charger to the wrong terminals (he remembered there was no voltage reading from the charger's meter).
It's many years since I last used jump leads but distinctly remember negative to negative terminals. What has changed and is it safer just to call out a breakdown company to do the jump starting?
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If the Corsa started fine then how was the ECU fried, what part of the ECU did not function. Regards Peter
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What has changed
Essentially nothing, except in the interim it has been realised that it's safer not to have the spark when you make the last connection happen directly by a battery - with the risk of explosion that entails.
As long as you follow, to the letter, the guidance given in both cars' manuals you'll be OK.
Connecting a battery charger backwards will fry ECUs immediately except on some quality cars where there is a protection relay that disconnects the ECUs in this event.
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>If the Corsa started fine then how was the ECU fried, what part of the ECU did not function.>
Engine revving up and down uncontrollaby, almost impossible to drive. Brought to dealer who diagnosed a failed ECU. I assumed that the jump start had something to do with this or the earlier attempt to charge the battery.
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Just because its claimed the ECU has been fried (it is possible from wrongly connected leads, or incorrect charging) dont just assume so.
If the car had a very flat battery and has not been fully recharged, and/or the alternator is not charging properly it is quite likely the wrong voltages are being distributed and the ecu is merely confused and cannot control the engine properly.
1st step is to fully charge battery and establish charging system, and then, and only then, decide what the car is doing.
You could easily end up repairing something that isnt broken!
Like wise, you cant work out what to repair until the above is in correct order.
hth
Edited by yorkiebar on 14/09/2008 at 17:49
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Galad, Was the key in the ignition of the dead car & was the battery fully discharged/
Ist remove keys from both vehicle ( some vehicles now the ECU become live with the key placed in the barrel before its even turned)
Connect the posotive & negative as you have stated then leave the cars for 5 minuets to allow the flat battery time to start recovering.
Then start slave car & leave for 5-10 mins to allow the volatge & charge rates to stabalize.
then attempt to start vehicle with flat battery but do not rev & imidiatley remove leads.
I doc
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I'm with Yorkie; I'd be a bit suspicious of a "fried ECU" diagnosis in those circumstances too. Sounds far more like an air leak and lost learned values. You'd need a large charger to reverse a battery's polarity - and there would be smoke.
The crux of using jump leads is never to use them on Mercs and modern French cars [recover to specialist/dealers for re-booting] and to leave them on for at least 2 minutes after the car starts. That's the danger zone.
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>The crux of using jump leads is never to use them on Mercs and modern French cars [recover to specialist/dealers for re-booting] and to leave them on for at least 2 minutes after the car starts. That's the danger zone>
Thanks Screwloose. I've now removed the jump leads from FiL's new Scenic just in case!
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you can get anti spike jump leads to protect car electrics from power spikes or surges or also the surge protection can be bought on its own to fit to existing jump leads
takes the risk away
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