BMW 525i Jump Start Damage

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Paul - 03 Jan 2005 07:12 GMT

I used my 86 BMW 525I to jump start another car and connected the
jumper leads in reversed polarity! (silly me thought a black wire was
negative in all parts of the world). The BMW now starts but will not
idle at any speeds. On starting it fires up ok but then dies and I
have to gun the accelerator to keep it going before it dies again etc.
Can anyone tell me which component of the electrics I should look at
first, coil?

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John Burns - 03 Jan 2005 13:06 GMT

> I used my 86 BMW 525I to jump start another car and connected the
> jumper leads in reversed polarity! (silly me thought a black wire was
> negative in all parts of the world). The BMW now starts but will not
> idle at any speeds. On starting it fires up ok but then dies and I
> have to gun the accelerator to keep it going before it dies again etc.

On Jet-L cars isn't the idle control valve controlled by it's own
electronics pod instead of the main fuel injection control unit? This
would do it.

You've been lucky BTW. A mate did the same thing with his 82 635CSi and
needed a whole new fuse box!

I had a 318i with your problem, the throttle position switch was out of
adjustment.

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Dave Plowman (News) - 03 Jan 2005 16:57 GMT

> You've been lucky BTW. A mate did the same thing with his 82 635CSi and
> needed a whole new fuse box!

I'm curious about the theory behind this. Damage to the car with the flat
battery might be possible, but in the OP's case, his was the 'donor' car.

Can't see a flat battery causing polarity reversal to a good one.

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Zon - 03 Jan 2005 21:59 GMT

> In article <41D9435B.1A72@unixnerd.demon.co.uk>,
>
> I'm curious about the theory behind this. Damage to the car with the flat
> battery might be possible, but in the OP's case, his was the 'donor' car.
>
> Can't see a flat battery causing polarity reversal to a good one.

Paul; was your car running when wires were connected? If it was, load dump
can cause lot's of damage.

BR:Z

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