Is this my battery, or alternator?

Need technical Q/A then you're in the right place

Moderator: martauto

Post Reply
User avatar
Endless325
E30 Zone Newbie
E30 Zone Newbie
Posts: 170
Joined: Sat Apr 28, 2007 11:00 pm

Tue May 15, 2007 12:13 am

Last week, after a long run, over 100 miles, I parked the car up for a entire week, tried to start it yesterday, dead. Put it on a 24hour charge, started fine, but I did'nt drive it, then restarted it a couple of hours later to take it for a spin, it's night, so all lights on, and heater, but thats it, took it up the by-pass, all good, on the way back, started to notice ALL the lights, interior/exterior getting really dim, couple of roads away from mine, starts to jump and misfire like a pig, finally cuts out, on my road! Tried to restart, surprise surprise, doesn't fire up, just clicks like mad, pushed it back into my drive.

So, is this my battery, or alternator, also remember I have been experiencing a misfire when the car warms up.


Cheers!
tailoutcharlie
E30 Zone Addict
E30 Zone Addict
Posts: 2164
Joined: Tue Feb 20, 2007 11:00 pm
Location: south wales

Tue May 15, 2007 12:20 am

seems like alternator to me but im no expert, sure some knowledge will be along in a minute :)
Chris
Image
Templ8e30
E30 Zone Addict
E30 Zone Addict
Posts: 2801
Joined: Mon Jan 10, 2005 11:00 pm
Location: Ashton-under-Lyne, Lancashire

Tue May 15, 2007 12:35 pm

I'd suspect an alternator or charging circuit fault.

However you managed 100 miles without a problem and had a bat flattery after a week, could be the diode pack going on the alternator draining the battery or could well be a duff battery as well.

Cheers,

Iain T
Image
2007 Mazda 6 2.0 estate
Political Correctness - A concept based on the idea that its possible to pick up a turd by the clean end !
DaveD
E30Zone Wiki Specialist
Posts: 5129
Joined: Tue Jan 11, 2005 11:00 pm
Location: Sheffield

Tue May 15, 2007 12:40 pm

happened to me on the fiat...alternator ...new diodes or brushes
User avatar
Brianmoooore
E30 Zone Team Member
E30 Zone Team Member
Posts: 49353
Joined: Mon Jan 10, 2005 11:00 pm

Tue May 15, 2007 12:45 pm

Get a meter on it!
What's the voltage across the battery with the engine at fast idle?
What's the voltage at fast idle with the headlamps on?
Any measurable voltage between the body of the alternator and battery negative?
What's the current drain between the negative pole of the battery and the battery earth lead with the lead off and the car stopped?
Cromanian
E30 Zone Newbie
E30 Zone Newbie
Posts: 65
Joined: Sun Dec 04, 2005 11:00 pm
Location: Kerry, Ireland
Contact:

Tue May 15, 2007 2:43 pm

Happened to me with my old 316, turned out the brushes were knackered on the altanator
DaveD
E30Zone Wiki Specialist
Posts: 5129
Joined: Tue Jan 11, 2005 11:00 pm
Location: Sheffield

Tue May 15, 2007 4:29 pm

not worth having it fixed if it is the alternator

spotted this
http://cgi.ebay.co.uk/BMW-3-5-Series-Z1 ... dZViewItem
Cromanian
E30 Zone Newbie
E30 Zone Newbie
Posts: 65
Joined: Sun Dec 04, 2005 11:00 pm
Location: Kerry, Ireland
Contact:

Tue May 15, 2007 4:48 pm

Why is it not worth getting fixed, I got new brushes and contacts put in mine for ┚¬20, and then my rad hose blew and I got it reconditioned for ┚¬60 worked perfectly.
User avatar
Endless325
E30 Zone Newbie
E30 Zone Newbie
Posts: 170
Joined: Sat Apr 28, 2007 11:00 pm

Tue May 15, 2007 4:56 pm

Thanks for all the help so far guys, haven't had a chance to do any of the above yet, but this afternoon when I came home for lunch, I started the car and put it in the garage, no problems, started fine?
User avatar
Endless325
E30 Zone Newbie
E30 Zone Newbie
Posts: 170
Joined: Sat Apr 28, 2007 11:00 pm

Sat May 19, 2007 4:32 pm

OK, bought a brand new battery from Halfords, was reading 12.6 volts before I put it in the car, started fine, but the volts did not jump at all when I statrted the car, neither did it at fast idle or a bit of a rev, and the more things I switched on (all lights heated rear, heater, brake lights etc.) the volts just kept on dropping, even with everything on and a bit of a rev, the volts didn't rise at all!

So I take it, it's the alternator thats had it?

What's a decent price to pay to get a new one fitted?

Is this one (cheers DaveD) http://cgi.ebay.co.uk/BMW-3-5-Series-Z1 ... 0112531682 good for a 325i?

Thanks once again everybody!
DaveD
E30Zone Wiki Specialist
Posts: 5129
Joined: Tue Jan 11, 2005 11:00 pm
Location: Sheffield

Sat May 19, 2007 5:05 pm

It says so but ring lucas with that part no and check.

.GSF is £69.50 plus vat for one

fitting is easy even i could do it myself 8)
Last edited by DaveD on Sat May 19, 2007 5:06 pm, edited 1 time in total.
User avatar
Brianmoooore
E30 Zone Team Member
E30 Zone Team Member
Posts: 49353
Joined: Mon Jan 10, 2005 11:00 pm

Sat May 19, 2007 5:05 pm

Check that the alternator is earthing properly first! Put your volt meter between the alternator casing (cleaned part) and the battery earth point with the engine running. Should be no appreciable voltage.
If this checks out OK, unscrew the regulator pack from the back of the alternator (two small cross head screws) and check the length of the brushes.
If they are worn out, then get a pack from a scrapyard with the longest brushes you can find, or it's possible to buy a new pack.
User avatar
Endless325
E30 Zone Newbie
E30 Zone Newbie
Posts: 170
Joined: Sat Apr 28, 2007 11:00 pm

Sat May 19, 2007 5:28 pm

DaveD, it's just that the alternator on ebay says its 12v and the original bosch one is 14v isn't it?

Brian,

I did as you said 0 volts across areas 1 and 2, but on area 3 first it read 11.63, then I waited 30 secs tried again on area 3, and 0volts, waited again the 0, waited some more, and 11 again?

Image
User avatar
Brianmoooore
E30 Zone Team Member
E30 Zone Team Member
Posts: 49353
Joined: Mon Jan 10, 2005 11:00 pm

Sat May 19, 2007 5:36 pm

If you have measured any voltage at any time between areas 1, 2 or 3 and battery earth, then take the alternator off, clean up where the mounting bolts go and reassemble. Take the air filter/AFM off for access.
User avatar
Brianmoooore
E30 Zone Team Member
E30 Zone Team Member
Posts: 49353
Joined: Mon Jan 10, 2005 11:00 pm

Sat May 19, 2007 5:39 pm

The ebay alternator is the correct one. 14 volts is the actual output to charge a 12 volt system.
That's a good price for a new alternator complete.
Note: with exchange alternators you don't normally get a pulley with the new one, so make sure you remove your's before you hand the old unit in.
User avatar
Endless325
E30 Zone Newbie
E30 Zone Newbie
Posts: 170
Joined: Sat Apr 28, 2007 11:00 pm

Sun May 20, 2007 2:02 pm

Brian, seeing as a replacement alternator can be had on the cheap, should I just buy a new one, as I really need the car back on the road sharpish, and a new alternator will cure my problem one way or the other won't it?

Also, when I'm buying a new belt for it, will it be the same one that fits the Bosch alternator, for the new Lucas one?

Do you think the misfire I'm experiencing when the car is warmed up is related to this, or is this just wishful thinking?

Thanks! 8)
User avatar
Brianmoooore
E30 Zone Team Member
E30 Zone Team Member
Posts: 49353
Joined: Mon Jan 10, 2005 11:00 pm

Sun May 20, 2007 2:19 pm

If it's running off battery only, it could well be responsible for a misfire.
If it's the alternator earthing that's the problem, then fitting a new one will cure it, just like taking the old one off and refitting it will. I suspect many alternators have been replaced because of earthing problems, and their owners are still non the wiser!
Went into a workshop once, where they had just changed a £250 alternator and a £200 battery in the previous week, and still couldn't get it to charge. Took me a couple of minutes to slacken off one of the alternator mounting bracket to engine block bolts and re tighten it. Problem solved!

If you remove the regulator pack from your existing alternator, just pull at the brushes slightly, and refit the pack, your car will probably work again for a few thousand miles.
User avatar
Endless325
E30 Zone Newbie
E30 Zone Newbie
Posts: 170
Joined: Sat Apr 28, 2007 11:00 pm

Mon May 21, 2007 12:43 pm

OK Brain, will do as you say before dishing out for a new alternator, probably won't ahve time until the weekend though! Thanks for everything so far, much appreciated as always! 8)
Post Reply