Starting Charging issue
 

im having a charging and i think related starting issue with our 01 3.0 x5.
at idle the battery looses charge. new battery and new alternator. the car has always cranked slow but i noticed the cable on the cowl (when you jump the car) is very hot and if you jusp the dead battery atunder the hood the car cranks very fast. much fast then with even the fully charged battery. my question is could a bad/crusty cable fronm the starter to the alternator be the cause if my slow starting and weak charging? replace both cable to the starter and maybe a new starter since its almost winter and i dont want to do it in the cold.
thanks for any suggestions
ray

It sounds like you have poor connections or maybe a poor BST connector. If you don't have a multimeter and know how to use it it's just guessing though.

I am battling something similar.

I have a cheap cig lighter voltmeter. Very handy...

At 1500 rpms and higher, I am getting 13.1 to 13.7 volts and it jumps around.
At idle, stopped at a stop light, I am getting 11.7 to 12.1 volts and it jumps around.

I was sure it was a voltage regulator and I replaced same with no change.
This alternator is a Bosch "Premium" rebuild of unknown age, but it is actually a Valeo 120amp alternator. It looked the voltage alternator had never been touched.

I have a new (not rebuilt) Valeo alternator on the way

OP- when you say you have a NEW Alternator in it, is it actually new or rebuilt?
I am hearing a lot of troubles with Bosch Rebuilds...which are no longer actually owned by Bosch btw...

The hot jump terminal is likely a big clue in your case....Maybe there is a short somewhere in the starter/alternator/jump point circuit.

whats is a BST connector?

its a new alternator not a rebuild. using my handheld scanner i get about 12v at the battery above 1500 rpm but it starts to drop down to 11.0v sitting in traffic at idle no accessories on

I don't mean to keep pestering. But is the New alternator a Genuine BMW, Bosch or Valeo ?

There are a bunch of aftermarket new alternators

The BST connector is the emergency disconnect at the battery. You are by- passing the battery connections and BST when you are boosting under the hood. Definitely clean up the boost connector, it shouldn't be getting really hot.

The alternator should be putting out more like 14 volts when the car is running. However, the battery is on the other side of the car so you should get your DMM out and check voltage under the hood.


Stranger things have happened, than buying a new alternator that is bad from the factory.

under the hoood at idle is 14.3 ish about 12.4 at the battery

Follow the heat. That's where the high contact resistance is causing voltage problems. The cable from battery comes first to that connector on the cowl and from there to starter and alternator.