BMW M5 Forum and M6 Forums banner

1 - 10 of 10 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter #1
Hi everyone, I've been lurking for quite a while, and generally just search the forums until I find the info I am looking for. Today, however I am struggling.

Last night I was out driving when it was very cold outside (-30 degrees C). As I was driving, I lost nearly all my electrical power, the headlights/taillights went dead, the radio went dead, the blower fan turned off, the dash stop showing readings. While all this was happening, the car engine was still behaving as normal. No stutters/no stalls.

My initial thought was the alternator. After speaking with someone, they told me that if it were the alternator, the engine would have stalled as there wouldn't be enough electricity to keep it running.

Eventually all power returned and the whole electrical system seemed to be functioning as normal.

Any ideas of where to start to diagnose this?

Thanks for any help/suggestions!:1zhelp:
 

·
Registered
Joined
·
2,415 Posts
Check the fusible link. It's a two to three inch long bit of metal that is on a spur cable coming from the Red Positive terminal of the battery.

The cables that attach to this bit of metal are held in with bolts that often come loose over time.

If it partially loses connectivity, you will at least lose windscreen wipers, interior blowers and electric windows.


Be aware this is the positive, so if you are risking it by checking it and trying to do up bolts when still connected, be sure not to touch the chassis or anything!! Best to remove battery terminals to be safe.

Regards

Ivan
 

·
Registered
Joined
·
7 Posts
Discussion Starter #3
Thanks Ivan,

I checked the fuse it seems to be well bolted down. I recharged the battery, took the car for a drive and it seemed to behave fine. I went through the records for the vehicle, the alternator was changed in Nov. 2005, and the car has since traveled 25,000km. It is a re manufactured oem bosch unit. I wouldn't think the alternator would be having issues.

I also checked the tension of the belt, it seems to have proper tension (based on my uneducated guess...I can push the belt 7-8 cm with moderate force of the fingers)

I do get some belt noise when it is very cold outside <-25º celcius, I wouldn't think a slipping belt would cause these issues right? A slipping belt would cause the engine to have poor performance aswell. Correct?

Theoretically, when there is a shortage of electricity in the system, does the power available get alloted to the engine, or is the electricity spread about the whole electronic system? Weird/Stupid question.
 

·
Registered
Joined
·
288 Posts
Hi, you can check the alternator my metering the battery voltage when the engine is running. When my alternator went everything did'nt cut out at once, first the stereo died, then the ABS light came up, then the suspension went to hard setting and finally the engine stalled. All this over a period of 5-10 minutes, for things to cut out instantly your problem is more likely to be a loose connection somewhere,

MIKE.
 

·
Moderator Emeritus
Joined
·
4,273 Posts
The gradual phasing of DME driven non critical systems is indicative of charging
issues as it drops non priority systems to support what output
voltage remains within the battery.

The alternator rarely fails completely...its a Bosch unit & fully serviceable.
Stripped many of them.
Often, it will be a brush or both,
An under performing regulator.
Some time the commutator ring on the main shaft ovalises on the shaft.
It knocks out one brush usually.
This should be supported by rear bearinf replacement.

Its rare for diodes to fail.
These are mounted in three rings of three inside.
You can have a couple of these fail & still have a generally functioning
alternator.
There is a method of telling this using the instriment cluster warning light.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #6
Just updating the situation in case anyone run into the same troubles. I wasn't able to find much info when I searched.

I replaced the alternator and it cleared up the problems. I suspect as was mentioned that it was the voltage regulator. I decided to replace the whole alternator rather than taking the risk of buying a new regulator, installing it then having the problem return.
 

·
Registered
Joined
·
1,289 Posts
Hi, you can check the alternator my metering the battery voltage when the engine is running. When my alternator went everything did'nt cut out at once, first the stereo died, then the ABS light came up,
Textbook failure on mine today - we're just off to go tow the thing 25 miles home, so we can repair the alternator :(
 

·
Registered
Joined
·
7,660 Posts
Textbook failure on mine today - we're just off to go tow the thing 25 miles home, so we can repair the alternator :(
What a way to begin the bank holiday weekend !

Don't let it get you down Nebpor .....and enjoy the rest of the weekend !

D
 

·
Registered
Joined
·
1,289 Posts
Thanks mate, left my girlfriends house at 10:30am to take her to a wedding, thought the car turned over a little lazily, then about 200 yards down the road the stereo stopped working and the check control chimed "Brake Circuit Lt", which isn't even in the manual!

The ABS light then came on, and when I pushed an electric window switch all the guages (fuel, temp, revs) dropped to zero!

I decided to turn the car off, then it wouldn't restart, sounding like a flat battery.

Disaster! I had to get her to her important wedding (not her own :blink:), so phoned my mate who lives near me (she lives 25 miles from me) to come up in one of my other cars and bring jump leads. Car started fine on the leads, but immediately stopped when the jumpleads were removed.

Things were getting late, so had to hot-foot it in spare car the 60 miles to her wedding, stopped in at my tuners place to grab a multimeter, then headed back 60 miles to look at my stricken M5.

It was obvious there was nothing coming out of the alternator, plus battery itself looked fine. We couldn't find any evidence of dodgy earths or short circuits either thankfully.



We then had to drive back to mine (25 miles) to pick up my mates other car so we could tow the M5 - my wee Rover 214 he originally turned up in was never going to make it and I couldn't risk the clutches on either of my two stripped out Integras, they don't make good tow cars!

Whilst home, I found this thread and hence confirmed the alternator theory, so no point in attempting any more diagnosis with the car at side of road.

Popped into Halfords for a tow rope, then 25 miles back to Glasgow and we went for a curry to cheer ourselves up after a long day and let the traffic clear rather than tow a car through rush-hour city traffic.

After eating so much I felt sick :7: we hooked up to his old Accord 2 litre, and then dodged the evening Glasgow traffic and towed the M5 home down the backroads - without assistance the brakes are a nightmare on it and there were lots of hills!

Finally got home with car safe at 8:30pm tonight, then just nipped out there for a pint ... I'm off to bed shattered now, but at least with
a) safety of car home and
b) knowing it's just an alternator repair, and that's a doddle really ... we'll do it during the week.

Ah well, also explains why car felt a bit flat last night when I was driving it pre-break - voltages were probably a bit low hence engine not running well.

Thanks for the words mate - I appreciate it, but all done now :applause:
Stephen
 

·
Registered
Joined
·
7,660 Posts
Well done for the positive outlook Stephen ......Life only becomes a drag when we feel that we have a God given right for everything to be complication free !

I Hope that she's all sorted and back to her best soon !
 
1 - 10 of 10 Posts
Top