Trouble jump starting

[HenryHippo]

Broken barge (BMW E38) has a flat battery (something is draining the battery when the car is turned off). I connected red cable from positive battery terminal on the donor car to the positive point on the BMW engine. I connected black cable from negative battery terminal on the donor car to the earthing bolt on the BMW. Donor engine then turned on.

Encouragingly the interior lights on the BMW came on, as did the dashboard. I waited 5 mins, then attempted to start the BMW. There was a click, but the engine didn't start.

I then waited a full 15 mins, but this time the BMW lights & dashboard no longer came on. There was no click when I attempted to turn the engine on.

Any ideas why a 5 min idle was enough to turn the interior lights on, but the second idle did nothing?

And how to attempt it next time?

[ninjacost]

HenryHippo said:

Broken barge (BMW E38) has a flat battery (something is draining the battery when the car is turned off). I connected red cable from positive battery terminal on the donor car to the positive point on the BMW engine. I connected black cable from negative battery terminal on the donor car to the earthing bolt on the BMW. Donor engine then turned on.

Encouragingly the interior lights on the BMW came on, as did the dashboard. I waited 5 mins, then attempted to start the BMW. There was a click, but the engine didn't start.

I then waited a full 15 mins, but this time the BMW lights & dashboard no longer came on. There was no click when I attempted to turn the engine on.

Any ideas why a 5 min idle was enough to turn the interior lights on, but the second idle did nothing?

And how to attempt it next time?

Sticking starter motor ? bad earth? , water ingress ?

Edited by ninjacost on Friday 15th January 19:09

[randomeddy]

Your battery could be totally goosed, not taking a charge.

Edited by randomeddy on Friday 15th January 19:35

[ninjacost]

Jump leads in good condition ? connected to batteries securely?

[Jamescrs]

Battery is too far gone for jump starting is my first thought, have you tried using a proper battery charger on it for an overnight charge?

[HenryHippo]

I don't understand why on the first attempt, the battery showed some response but nothing at all on the second attempt. Clips were secure and I didn't move them between attempts

jump leads are in a decent condition... 3 years old but only used a few times.

[HenryHippo]

Jamescrs said:

Battery is too far gone for jump starting is my first thought, have you tried using a proper battery charger on it for an overnight charge?

No don't have that facility. I am thinking to let it idle for 30 mins first time next time, before jumping... then driving straight to the garage of course

[ninjacost]

HenryHippo said:

I don't understand why on the first attempt, the battery showed some response but nothing at all on the second attempt. Clips were secure and I didn't move them between attempts

jump leads are in a decent condition... 3 years old but only used a few times.

could you not just try donor battery on bmw ?

[Scootersp]

You can hold the revs higher on the donor car (could try a different donor car too perhaps) when you try if you have an assistant, did you try it just before you posted this? It's very cold out and every little helps.

On the bmw I'd be tempted access the battery in the boot and jump it from there.

[Scootersp]

Does it perhaps sort of shutdown, did you lock/unlock on the key fob before trying........sorry if obvious just trying to think of the simple things.

[HenryHippo]

Scootersp said:

You can hold the revs higher on the donor car (could try a different donor car too perhaps) when you try if you have an assistant, did you try it just before you posted this? It's very cold out and every little helps.

On the bmw I'd be tempted access the battery in the boot and jump it from there.

thanks! I'll try a friends donor car and revving! If not, then I'll jump the battery

ninjacost said:

could you not just try donor battery on bmw ?

take the battery out of the donor car and install it into the BMW? I wouldn't feel confident doing that... it's a bit smaller battery too (2.2 litre Honda)

Scootersp said:

Does it perhaps sort of shutdown, did you lock/unlock on the key fob before trying........sorry if obvious just trying to think of the simple things.

I unlocked the BMW before starting, but the flat battery meant the button wasn't working, I had to manually unlock the door

[HenryHippo]

Just remembered that the donor car battery is getting on a bit... it's a little more than 5 years old/ 45k miles and it's a smaller car than the BMW too. Will try with a friends car next.

[Matt_E_Mulsion]

Your jump leads are most likely not up to the job. Most off the shelf jump leads are really really poor quality with hardly any copper core in them. If you cut the cable you would find that most of the thickness is just the insulation.

[eltax91]

HenryHippo said:

Just remembered that the donor car battery is getting on a bit... it's a little more than 5 years old/ 45k miles and it's a smaller car than the BMW too. Will try with a friends car next.

Age of the battery on the ‘jump’ car shouldn’t matter as long as the engine is running when you attempt the jump. As others have said, pick the revs up a bit from idle on the jump car before attempting start on the bmw.

Definitely try direct onto the battery and not through the engine bay points if you can. Reduces any chance of a bad earth or a drop in cranking amps across the length of the cable

[Honeywell]

Get a CTEK smart charger. I've had a similar failure to jump start a similar age car. 24hrs on the smart charger nursed the dead battery back to good health. Given modern batteries are ~£150 it's well worth the investment.

[GreenV8S]

If you get a volt meter and measure the voltages across the battery and starter motor while you're trying to start it you can eliminate a lot of guessing.

[Penelope Stopit]

Matt_E_Mulsion said:

Your jump leads are most likely not up to the job. Most off the shelf jump leads are really really poor quality with hardly any copper core in them. If you cut the cable you would find that most of the thickness is just the insulation.

This

and

ninjacost said:

could you not just try donor battery on bmw ?

There's nothing wrong with trying this, anything is better than nothing and a smaller battery will still power a starter motor even if it does turn the engine over slower than a bigger battery

[HenryHippo]

Matt_E_Mulsion said:

Your jump leads are most likely not up to the job. Most off the shelf jump leads are really really poor quality with hardly any copper core in them. If you cut the cable you would find that most of the thickness is just the insulation.

They jumped the same car, with the same donor car multiple times, 3 years prior and have been kept in a dry boot since

Took the donor car to Halfords for their free battery check.... it's in very good health despite its age

Edited by HenryHippo on Saturday 16th January 15:12

[paintman]

In which case sounds like either the connections of the jump leads are bad or something's gone pop in the BMW. Any master fuse anywhere?

[Spare tyre]

Measur voltage on buggered car

Have jump leads connected to running do and car for 30 mins

Disconnect then measure voltage on buggered car

Give starter a whack

You’ll be surprised how cheap batteries are from ecp with a discount code,