Only Starts When Jumped?

[DaButt]

Hi, so my brother is looking at a euro spec 1992 520I, I believe thats an m50b20?

Anyway, it sounds like the car is in decent daily driver shape except for one glaring issue: the car has to be jumped.

That's pretty much what I know. The car is in Italy, I'm in California, so I can't contribute too much more than research.

It seems like once it's started it runs fine, but obviously my brother would like to fix it. Any ideas what parts? To me it seems that if it starts under jumped power but does nothing without a jump, it's either the battery or the alternator. Well, the seller says he just replaced the battery. So I'm thinking this is all alternator. Any other speculators or ideas? Am I on the right track?

Thanks for any help, guys.

[JonnyOg]

Dead batt for sure, possibly alternator issue. That is about all it could be.

[DaButt]

Sweet, thanks for the confirmation. Does anyone disagree with my and jonny's assessment?

[AndrewBird]

If the alternator died, the battery would have slowly drained until dead. If the battery was then replaced, the same thing would happen again.

Have your brother start the car and measure the voltage across the battery. Should be around 14v. If it's lower, the alternator is likely dead.

[JinormusJ]

Only Starts When Jumped?

I just dealt with electrical gremlins last week. My car had to be jumped every morning. Turned out my battery and alternator were fine

So I grabbed a multimeter and measured 500mA drain on the battery with no lights on (stock is 20-30mA drain)

I tested each fuse by unplugging it and measuring the current drain at the battery one by one; nothing stopped the drain

Then I unbolted the main terminal, a small black "box" located on the passenger side of the engine bay that has a little red plus sign on it, and tested all 3 terminals using the multimeter

Long story short, I ended up finding that the drain was my ABS sensor, and after checking my ABS relay I saw my wiring was shorting and causing a slow drain.

After a few minutes I fixed the issue and my car doesn't drain anymore

TL;DR
Check wiring using a multimeter if possible. Electric gremlins aren't always "Battery + Alternator"

[Das Delfin]

If the alt and batt are both dead, the car will die as soon as you disconnect the jumper cables. If the car has been sitting around for a while, even a year-old batt will be done.

Electrical problems aren't hard to deal with. You just have to get a book with some wiring diagrams and use that to hunt them down. It helps if it's warm outside.

That being said the furthest I've ever driven to buy a car has been 20 mins away.

[Old city bimmer]

sounds like a dead battery. like mention check voltage when the car is running across the battery terminals.