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735owner View Drop Down
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Direct Link To This Post Topic: Alternator Question
    Posted: 14-November-2005 at 14:11

I have a 1989F reg 735I SE with a dodgey alternator. There are 2 models for that year 115amp & 140amp.

I have the 115 Amp model, does any one know If I can replace it with the 140 Amp version.

I.E. are the connectors the same and will it do any harm to the 'computer'/voltage regulator etc if the 140 amp version is used. .

 

Many thanks in advance.

P.S. does anyone know where to get a 115A one cheap ?

 

 

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shogun View Drop Down
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Direct Link To This Post Posted: 14-November-2005 at 22:54
No problem at all, you can use both of them. The voltage regulator will handle that.
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Direct Link To This Post Posted: 15-November-2005 at 05:43

Thanks Shogun,

I've been finding it hard to locate a salvaged 115A replacement so I'll just get the next 140A I find and try it.

 

 



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Direct Link To This Post Posted: 16-November-2005 at 12:57
Are you sure it is the alternator and not the voltage regulator? You can buy these seperately.
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Direct Link To This Post Posted: 17-November-2005 at 05:25

Hi eta,

How do I tell which is at fault: voltage regulator or the Alternator ?

I'm only going on what the AA man said but I do have my reservations about his diagnosis as the charging light is behaving normally, I.E. it goes out when the car is started.

I'll detail what happened:

 Driving a couple of miles back from the cinema at night ( lights, demister etc all on ) get to 100 yards from the girlfriends  and all of a sudden the ABS light comes on followed 10 seconds later by the computer 'binging' a couple of times as it goes through its start up routine ( normal at start up reporting a couple of non existent faults ). Anyway I park it and then the windows are taking an age to wind up,  So I switch off and try to restart and I get 'click click click' and no engine turn over: All the classic signs of a flat battery ( Which I had replaced in 1999 ).  Being late I left it at that and then had another look at it the next morning, to my surprise it started 1st time as though nothing had happened ??? puzzled I let it run for 20 minutes it the hope of putting some charge back into the battery. Then switched it off and tried to restart 'Click click click' flat battery again. Then I called out the AA and he said it was the Alternator although he was not able to test this directly as all the cables are hidden behind a plastic cap underneath the Alternator. He jump started it, put a meter accross the battery and it read 9.2v. After that he disconnected his lead and we talked for 15 minutes while it Idled in the background, all of a sudden it started coughing, he reconnected his jump leads and it immediately settled down again and the computer went through its startup routine.

So I'd say I definitely have a lack of voltage but how do tell whats the cause. The battery is a 'sealed' unit and you cannot visually tell if there is a problem ( thats progress for you ) but I have left it on charge over night and it has behaved like it should I.E. the current meter on the charger gradually decreased over 16 hour indicating it was drawing less and less current to charge.

Unfortunately I don't have a Digital voltmeter, just the old needle display type and so I can't really do an accurate 'Voltage' drop test.

 

How does one do a Voltage regulator test.

Many thanks for all and any responses

 

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Direct Link To This Post Posted: 17-November-2005 at 05:47
I am not a techy, but know that occasionally the regulators pack up. Could it be though that your battery is on the way out? If it is more than 5 years old, it is on borrowed time. Can you borrow a known good battery for a day or 2 to see if you have probs. Batteries can be intermittent and with the cold weather arriving they are all going to be hard pushed.
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Direct Link To This Post Posted: 17-November-2005 at 06:25

Whilst I have not ruled out the battery 100% I'm close to 98% certain that its not the problem.

 

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Direct Link To This Post Posted: 17-November-2005 at 09:28

I'd go along with the battery theory from what you've said.  A dodgy alternator or regulator would probably have been indicated by the battery warning light flickering on the dash for a few days before it died on you.

If the battery is duff, it may not accept a full charge but it can give all the signals that it is charging fully.  This happened to my bike battery earlier this year and I reluctantly changed it for a new one.  Turns out that was exactly the problem!

Even if the battery is ok, it will probably be about to pack up anyway after 6 years so you might as well get a new one to try it out.

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Direct Link To This Post Posted: 18-November-2005 at 05:53

Thanks for your input Chas.

This has left me in a bit of a quandary as I really didn't think the battery was the problem but now two of you are saying it is highly likely

Hmmmmmmmmmmm bug

These sealed/opaque units are a real pain in the butt if there is no way of simply testing them. All the other batteries I've ever had cause to look at ( plenty too many )  have been made of clear enough plastic so a visual inspection of the plates is possible and also one could see the fluid levels and take a hydrometer reading.

A new battery is circa £80-120 which is a tad expensive if its not the cause and also I'm currently transportless to obtain such a heavy item.

 

Anyone know a meaningful test for a battery ?

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Direct Link To This Post Posted: 18-November-2005 at 09:04
If you've got a helpful BM dealer they might deliver it to you on their daily trade parts van (all BM dealers have one). If you are a BMWCC member you should get 10% discount. Their batteries are not much more than other outlets and will be the best quality, usually go on for at least 5 years.
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Direct Link To This Post Posted: 26-November-2005 at 13:48

Managed to fit a new ( 2nd hand ) Alternator today. Bit of a tough job, much more difficult than the Water Pump replacement as the nuts/bolts were much less accessible. Just as I tightened up the last bolt from underneath the car a black square piece of plastic dropped on my head. Not really sure what it is or where it goes. Looks like it might be a spacer as it has a hole in it about the size of the lower bolt. Hope its not important as its definitely not going back on the car. 

Anyway its in and I'm nervously driving it about, dreading a repeat occurence of the symptoms as I, and no one else seemed to be 100% sure that was the cause of the problem in the first place.

When I took off the old alternator  I found a problem with the thinner of the two wires. It had snapped off the connector, Couldn't tell if I had done this just as I removed the plastic wire cover or if it predated my manhandling and in fact this was the whole cause of the initial problem. I don't think I broke it but can not be wholey certain.

 

Many Thanks for all your help on this BB.

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Direct Link To This Post Posted: 26-November-2005 at 16:16

Hi, I would agree with the others and get the battery checked, 9.2v on the AA mans meter is not good, you should get at least 12v or even 13.5 if chrging/fully charged. It would also cause a lot of suilly electrical faults.

Do you or a friend have a battery with similar terminals you can borrow for the day? Or get a known good secondhand one to try and if it cures probs then buy new one.

IanT
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Direct Link To This Post Posted: 28-November-2005 at 16:58

Just a quick update...... I've now done about 6 hours/80 miles most of them with the lights demister etc on full, opening and closing the windows and sunroof trying to use as much juice as possible and its still going so maybe it was the alternator after all. I plan to dismantle the old one this week to see if I can find any faults.

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Direct Link To This Post Posted: 29-November-2005 at 06:02
Well done, looks like we were all wrong!
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Direct Link To This Post Posted: 29-November-2005 at 16:55

Good news, now I need to sort my bro in law out, he's a mechanic, called me "as I'm into classic bmw's". His E30 won't start, whats wrong with it.

I asked what had happened since it last ran, he said it ran out of fuel (on it's own?) then he flattened battery turning it over.

I suggested he put at least 3 gallong of fresh fuel in with some injector cleaner, charge the battery, if it didn't work check plugs for spark and fuel getting through (remember he's a mechanic) - hadn't occurred to him.

I called him later to see how he'd got on and got told "a bloke" at work said it was always the coil or dizzy on old bmw's so he should go to the dealer and buy new ones.  I gave up.

IanT
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