I think this may have been covered before, but can anyone advise me of the dangers of using jump leads and ECUs.
I recently used a Micra to jump start another car and it later refused to start, and now runs badly.
What could be the likely trouble?
The hand book and workshop manuals detail the procedure, but give no disadvantages.
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Positive on charged battery
Positive on dead one
Negative on charged
then to earth on dead car.
Turn on all power drains on the dead car - fan, lights heated rear window etc
sounds like the ECU on the Micra's taken a knock. Try disconecting the battery, and letting it reset itself.
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The disadvantages are that the power spike generated can burn out fragile electronics, but this only usually affects the receiving vehicle, not the donor.
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Did you have your engine running before the connection to the donor car?
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No. The connection was made and then the donor engine was started, before attempting to start the dead car.
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Guy, earth first or last.....every manual always gives it as earth last in the sequence which ian describes. also don't know why either but imagine its for preventing arcing to electrical components and resulting damage.
ian...Turn on all power drains on the dead car - fan, lights heated rear window etc.
Did you mean off and not on....
alvin
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On.
Apparently it stops power surges, which can be damaging.
Both my old BMW and Opel mention it in the handbook.
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If the engine was running, why would he need a jump start?
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Voltage from the battery of the donor car WHEN RUNNING will be circa 14-16V and this will blow many of the fuses in fragile equipment such as car alarms etc.
Did this to my Clifford Concept 50 alarm once - never again!
Best way to do it is to jump from the donor car WITHOUT the engine running. This does require a decent battery on the donor car but at least the voltage will be as expected.
As opposed to Ian from SA - I always connect the earth first - not sure on the reasoning behind it tho!
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when connecting/disconnecting a battery, the reason for connecting positive first is to reduce the chance of causing a short. If the negative is connected first and the spanner happens to touch nearby metal while connecting the positive, a good shower of sparks can be produced.
Similarly, that is why the final connection (as Ian pointed out) is made to earth away from the battery, thereby reducing the chance of sparks igniting any hydrogen floating about. This should also be the first connection to remove.
A chap from work had a battery explode on him recently after charging, so it's a real possibility!
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I think you will find that fuses are blown by current, not volts but components could well be damaged.
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P reg Mondeo engine ran like @!#$ for the first 5 miles after a battery change, the ECU reprogammed itself by then & all was sweet again, has the Micra been run for any length of time since?
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We went here before lots of times. I was under the impression that the engine of the donor cart had to be running. Then positive to positive. Then negative to a metal bit of the engine or chassis of the receiving car because apparently this stops the overload that could occur from the two batteries together. So maybe starting the Micra effectively with, for example, a 22 volt battery (12.5 volts from the Micra + maybe 8.5 volts from the other car) has damaged the Micra or re-set its codes.
HJ
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Surely with the batteries connected in parallel, the voltage would still be 12v.
The batteries would need to be in series to produce more than 12v.
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Correct the batteries in parallel cannot be more than the battery with the highest voltage , batteries connected in series will add the voltage of both batteries (lorries use this).I too was under the impression that the donor car should have its engine running and i have used this method with no ill effects, if the engine is running the voltage can be around 14.7volts which can only give more power to start the faulty car.
Fuses are indeed blown by current but voltage is required to produce the current also , regarding spikes if the last connection is made quickly and firmly there should be no problem (poor quality electronic products aside) any electronic circuit should have a on board capacitor or capacitor / resistor network to absorb is , don't forget on a normal start up volts drop down around 9volts until the alternator quickly recharges up to 14.7 volts. sorry about the earlier post but I'm sure most people understood my meaning
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Sealed for life batteries should not be used to jump start if the recipient battery is very flat.
Mike
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The AA told me you can't jump start a battery completely devoid of charge(they were right in that instance too).
Rob F
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Really? I'm sure I have before now. Why?
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chedd
Have you solved the problem on the Micra. Sealey supplies jump leads with surge protection built in, also supply surge protection as a separate unit which clips across battery. Buy via motor factors.
Tony
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The Micra is now apparently running OK (it's not my car, although I used it as it was conveniently parked near the dead vehicle)
The owner called the RAC out and I am not sure of their findings.
(The owner, a lady, is glad that it is now working, but does not want to discuss the diagnosis: I think I am not in her good books at the moment!
I have a feeling that the donor battery was not at its best.
Thanks for everyones imput.
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