Persistent electrical / charging issue.

[mcbonio]

Was just out in my e30, I pulled over to drop a letter in the postbox with the engine still running and began to take off. Suddenly all the lights go dim, the radio flickers on/off and then dies and the engine idle begin to drop and start to stall.

I quickly gave it some revs and all lights went bright again and the radio came on and then was fine all the way home. I did not see the battery light come on either.

Does this sound like an alternator issue? Why would it all of a sudden loose power like this?

[johnl320]

Could be brushes in the alternator wearing out but could be something simple like a loose belt. Does your battery light come on when you turn the ignition on?

[mcbonio]

No, no battery light nor did it come one when the power was low and beginning to stall.

[johnl320]

Does it come on when you turn the ignition on but dont start the engine?

[mark_i]

worth checking that the alternator is earthed properly to the block.

[johnl320]

worth checking that the alternator is earthed properly to the block.

Check simple things, starting with battery connections are good, alternator belt is tensioned correctly, engine to chassis lead is good and as mentioned above, this is a common fault which I experienced on my old 320i and it started with batteries not lasting as long as they should followed by lights dimming etc.

[mcbonio]

Going to have a little nose in the garage now as I've got to get something fron there anyway.

Just to clarify earth points;

Alternator earths to engine block and then engine to chassis?

How many earth points should there be?

[johnl320]

one on the back of the alternator to engine, big one from engine to chassis

[mcbonio]

Cheers john, will report back.

[johnl320]

Just because they are in place doesnt mean they are making a good connection.

[mark_i]

depends on the alternator. M20 is earthed through the mounting bolts, M40/42 has a separate earth strap.
Then engine to chassis earth is on the sump on an M20, on the offside engine mount on an M42

[mcbonio]

Mines an m30.!

Just checked, engine is earthed to chassis.

Alternator has a plug which runs off deep into the engine.?

[johnl320]

did the battery light come on? My m30 hasn't got a strap on the alternator. Thought you had a four pot for some reason, soz

[mcbonio]

I also get dim lights when I first start it up, I give it a few revs and they brighten up.

I think the battery isn't very good anymore and not holding a charge. I think I'll take it for a load test, or isn't there a way I can do this at home?

[Rav335uk]

Yrsy that the alternator is charging, put a multimeter on the battery and see what voltage readings you're getting

[mcbonio]

Both with engine on and off?

[johnl320]

could be a diode breaking down, really need to see how much the alternator is putting out.

[Rav335uk]

With the engine running!!

[mcbonio]

11.8v engine off

11.2v engine on - Shouldn't this be around 14v when engine is on?!

Either my battery won't hold a charge or the alternator is barely charging the battery..?

[Rav335uk]

Alternators shagged by the sound of it.
Does the voltage rise when you push the LOUD pedal?

[mcbonio]

Not really Rav.! Mulls around the 11.3v mark.

I did try a pseudo load test by turning all the lights on when the engine was off. Went down to around 10.5v Which isn't a bad sign, if it were around 9v I'd say the battery was dead.

Looks like my alt is smoked.

I've put the battery on charge and I'll see how it behaves tomorrow. This could be the cause of my cold running issue, low volts from the battery and the alt not topping it up. Would insufficient power cause lumpy rich running until the car was in motion?

[Rav335uk]

Could do.
I would look at getting the bushes changed if they can be, or get it recon'd.

[mcbonio]

There is a port on the back of the alternator which holds he bushes, but I can't get it out easily as the m30 dipstick is in the way. I'll have to take the alternator out.

Any idea where I can get new bushes? BMW?

[Rav335uk]

According to the link below, it looks like the brushes are shared amongst most BMW alternators.

http://www.4wheelsautoparts.com/bmw-par ... -3269.html

[mcbonio]

Yes I've just noticed that on realoem, loads of bmw alternators use 'em.! I'll get onto cotswolds tomorrow. Should be a simple fix.

I've stuck the battery on charge, so I'll see if that holds its charge in the morning. If ok then I guess its the alternator.

Cheers Rav, John and Mark.! Legends as usual.

[Rav335uk]

I see you've put up a wanted add too

[mcbonio]

Yeah I put that up before I realized the carbon brushes might be at fault and I could change them.!

Pacerpete was on it like a fly on shit too.

[Brianmoooore]

Remove the regulator/brush pack, and if it is a worn brush (very short and signs of arcing on the end ), give this brush a gentle pull to straighten out the braid that holds it in place. Replace the pack in the alternator, and it should work properly again for a month or two, giving you plenty of time to get hold of a replacement.
No need to go to BMW for the regulator pack; it's a Bosch part, available from plenty of other sources.

[mcbonio]

Thanks Brian,
I charged the battery over night and it was at 13.5v when tested. I cranked the car and the volts went down to 12.8v, much perkier start than usual too.

I've just taken a trip to tesco and back, 3 miles. and the battery is now at 13.3v

So the alternator and battery are working ok it seems, perhaps I'm not using the car enough to maintain a good solid voltage, or perhaps I have an electrical drain somewhere.?

[mcbonio]

Still on this issue, . I drove home sticking to 30mph as there are cops everywhere here in December.

The lights went really dim for about 2 miles and when I arrived I shut the car off only to find it wouldn't start again...! I let the battery sit for 5 mins then tried again whist giving it gas and it fired up all lights nice and bright and the tacho and econometer working accurately and not flopping about like the usually do.

So today I ordered a new alternator regulator/carbon brush set and fitted it. It doesn't seem to have helped much, the tacho and econometer now are flopping about again and I still have to rev it past 3k to get the lights to brighten up.

Whats up with this? Bad battery?

[mcbonio]

Will have another look Willz! I'll get to the route of this. My missus e46 has a new battery, I'll put that in my mine and see if that helps at all.