Alternator faulty - thoughts? : N52 (Coupe)

N

Newbers

Active member
 St Albans (one days march from London)
Hi all,

Following some problems with a flat battery I took the car to KwikFit for a free battery/alternator check (seemed reasonable compared to the £60 my main stealer wanted!)

The guy confirmed that the battery was good (and that there was no undue drain with everything off) but that the output from the alternator was poor. Max voltage we saw was 12.4v (should be over 14v...)

He mentioned that a lot of modern cars use crap wire (in the looms) which can cause these problems and that I should check there's no obvious corrosion (which I will).

I have previous taken alternators to specialists who have changed the regulators etc. at a fraction of the cost of a whole new unit but that has been when the alternator has been completely dead. (It is against my religion to fork out for more than I need......)

Questions:
1. It looks relatively easy to get the alternator off (Remove air filter box, remove tension from idler pulley, then 4 bolts). Has anyone done this on an N54 engine? Anything to watch out for?

2. Any experience of low output from an alternator? (As opposed to dead)

3. Any experience of corroded wiring causing this type of fault?
 
Update. I took the alternator off (easy enough when you work out how to remove the tension from the idler pulley - I had to use a mirror to see).

I took the whole unit to a specialist (LR Gawley in Markyate - Old school experts!) Normally they will test the unit on their bench but in this case they said there wasn't much they could do as the output of the alternator is controlled by the ECU.

I've heard of some modern cars 'switching on' the alternator when the car is braking or on the over run as an efficiency measure but I wasn't aware that this was the case here. Anyone know anything about this?

He also said that in some cars it is necessary to reset the computer when fitting a new battery. I didn't quite understand why but I gather that otherwise the car will not properly maintain the charge of the battery (I'm slightly sceptical about this). Anyone know of this?

The guy was 90% certain that the problem would be the rectifier module which is replaceable. I've had to have this ordered in from Germany. Should be here Wednesday <> £50. He actually suggested taking it to BMW to test but I figured that seeing as it was already off the car and for the hassle of getting it booked in to the Stealers + their crazy prices it was worth a try.

I shall keep you posted.......
 
Thanks for correcting me srhutch (what a doofus!)

I've corrected the subject of first post.
 
Update. I got the alternator back (fitted with brand new regulator for £60 cash) earlier and fitted it.

Exactly the same :cry: very low voltage (well under 13v).

My only hope is that I'm barking up the wrong tree. As mentioned before the alternator output is apparently controlled by the ECU (or DME in BMW speak).

It's hard to find out much about this although I found a good article here: http://www.google.co.uk/url?sa=t&source=web&cd=7&sqi=2&ved=0CFoQFjAG&url=http%3A%2F%2Fwww.aftermarketonline.net%2Fewcommon%2Ftools%2Fdownload.ashx%3FdocId%3D23715&rct=j&q=modern%20electrical%20sytems%20alternator&ei=9O9nTvDiK8m48gP07ITyCw&usg=AFQjCNGb3RXJALrUxIWZFs_OUAhdCRoVqw
and another here: http://askpete-hella.com/2011/04/07/how-do-external-alternator-control-units-work/

I also read up on BMW Intelligent Alternator Control but I get the impression that was introduced after my car (Which is 2007). This is a cool system which switches the alternator on and off so that it creates no extra load on the engine when the battery is charged (or the engine is working hard) but charges when the car is decelerating.

I have one more test to do. Try decelerating with volt meter connected failing that I think I'll have to give in and ask the stealers.....
 
Don't believe we have Intelligent Alternator Control, think that is only part of the ED cars liek my 1 series.

If I get chance I will check my alternator output at the weekend.
 
Not a lot of interest in this post but in the interests of completeness it may help someone in the future.
I did a couple more tests. Whilst driving the voltage is up and down but never went over 13.3v. Interestingly I couldn't really see any impact from turning on the lights, heated seats, fan etc. It didn't seem to make any difference whether I was accelerating or decelerating.

I also realised that my multimeter has a 10A DC capability so I disconnected the battery and connected the ammeter in series. With the boot light disconnected the initial current draw was 2A but this went down in steps over a couple of minutes to 0.01A where it stayed for a couple of hours. This seems reasonable and has reassured me that there is no fault causing undue power drain when turned off.

So it seems the fault is either in the alternator itself (not putting out it's full capacity) or the ECU (a single from which is supposed to control the output of the alternator).

Specialist Cars in Luton tell me that the £60 test referenced above will include battery and alternator so I think that's the only option. (I hate having to give in and resort to the stealers).
 
Newbers said:
Not a lot of interest in this post but in the interests of completeness it may help someone in the future.
I did a couple more tests. Whilst driving the voltage is up and down but never went over 13.3v. Interestingly I couldn't really see any impact from turning on the lights, heated seats, fan etc. It didn't seem to make any difference whether I was accelerating or decelerating.

I also realised that my multimeter has a 10A DC capability so I disconnected the battery and connected the ammeter in series. With the boot light disconnected the initial current draw was 2A but this went down in steps over a couple of minutes to 0.01A where it stayed for a couple of hours. This seems reasonable and has reassured me that there is no fault causing undue power drain when turned off.

So it seems the fault is either in the alternator itself (not putting out it's full capacity) or the ECU (a single from which is supposed to control the output of the alternator).

Specialist Cars in Luton tell me that the £60 test referenced above will include battery and alternator so I think that's the only option. (I hate having to give in and resort to the stealers).
Click to expand...


I would be VERY surprised if the ECU was faulty.
Rather than spend 60 on a test, couldnt you seek a repalcement alt from a breaker OR if you know anyone else with an equivilant zed - ask them nicely to borrow there ALT for a test? :)
 
I like your positive view on the ECU Jamiez!

I did find an alternator repair place in Borehamwood on Google earlier. They told me they could test the output of the alternator by simulating the signal from the ECU and if knackered may be able to repair it. So that could be the next step.

Also my Dad has just lent me an OBD reader. I'm going to plug it in an see if there are any faults....
 
Newbers said:
Not a lot of interest in this post
Click to expand...


i was just sat reading this post with interest, maybe you ment not a lot help, its a new 1 so your slightly on your own, i'm sure many will be interested :thumbsup:
 
A little update. Specialist Cars in Luton came and collected my car for a service this morning. (I was delighted to see two old (late 60's /70's) guys come to pick it up rather than a boy racer 20 something!)
I asked them to set up a couple of key options (I want the three flash lane changing enabled etc.) Also to have a look at my battery charging issues.

I missed a call at 3.30pm but before I could call back the two old guys appeared to pick their car up - no sign of mine. Long story short. Dangerous to drive (I was planning to take it to Bradford tomorrow - a 400 mile round trip!) The alternator has been working fine, the problem is in a junction box under the bonnet (where the live to the starter motor, the connection for jump starting and the feed from the alternator connect) apparently.

It needs an £11 part which has to come from Germany (perhaps by Friday) and an hours labour (on top of the hours diagnosis).

I feel a bit silly that I didn't look a bit more closely at the wiring. They reckon what ever it is that is causing the problem has been glowing red which is slightly unsettling......

Top marks to Specialist for sorting out a 2002 318 for me at an hours notice though, and looking on the bright side I suppose it saves putting 400 extra miles on mine!
 
FYI -- While it may not be Intelligent Alternator Control, this is straight out of WDS for all E85/86s:

BSD interface to the alternator
The alternator with BSD interface can actively communicate with the engine control unit. The alternator is not linked to the charge indicator lamp, only to the engine control unit. The alternator can detect a variety of faults.

Function
The following functions have been implemented in the engine control unit for the alternator with BSD interface:
-Activating/deactivating the alternator on the basis of appliable parameters
-Specification of the maximum permitted degree of utilisation of the alternator
-Control of the alternator's load response
-Calculation of the alternator moment degree of utilisation
-Diagnosis of the data line between the alternator and the engine control
-Filing of alternator faults in the defect code memory
Activating the load control lamp in instrument cluster via CAN
In comparison to alternators used so far, the display strategy of the load control lamp does not change when the alternator with BSD interface.
The basic function of the alternator is also ensured if the communication between the alternator and the engine control is interrupted.
 
Thanks for that bcworkz

Useful info although I struggled to understand all of that! I did read up a bit more on the site and thought that some of the following was worth pasting here:


Load Response Function, Alternator Voltage Regulator

The alternator current changes abruptly by switching major loads. This load results in engine speed fluctuations when the engine is running at idle speed or at low speeds. In order to prevent this disturbance the load response function of the alternator limits the power increase at low engine speeds as engine operation is particularly susceptible to disturbances at these low speeds. The current increases at a rate of approx. 10 A per second at engine speeds below 1000 rpm. An unavoidable side effect of this function is fluctuations in the brightness of the headlights at idle speed.

The load response function is not active at medium and high engine speeds.

Fluctuations in the brightness of the headlights at engine speeds above 1000 rpm are an indication of a faulty voltage regulator.

Start Load Response Function

The start load response function prevents the alternator already supplying current during the engine start procedure. This results in a slight mechanical resistance for the starter ensuring improved starting characteristics particularly at low temperatures. .

The start load response function prevents the alternator generating current for up to 2 s after starting the engine. As a result the alternator current increases at a rate of approx. 10 Amps per second.

The starting characteristics can be severely impaired if the start load response function fails.

Alternator and Battery Wiring

Due to the alternator and battery electrical connections shaking loose or corroding the resulting contact resistance can be so high that the battery is no longer charged sufficiently. These conditions can also occur only intermittently. Simple visual inspection is generally not sufficient. Particular attention should be paid to the ground connection of the engine and body.

It is possible that the fault may be dependent on load as the engine can move within certain limits thus mainly affecting the connections in the engine compartment.

Alternator Voltage Regulator

The rectified voltage generated by the alternator depends on the electrical load and the engine speed. A regulator system is required in order to supply the electrical loads with a constant voltage. The alternator voltage is normally controlled to values between 13.5 V and 14.5 V. Large changes in the current load of the alternator (major loads cutting in or out) can cause the voltage to temporary deviate from this range. These swings, however, must not exceed 1 s.

Battery with magic eye status indicator

The battery cells are sealed. It is not possible to measure the acid level or density. A charge status indicator is installed for this purpose.

Important note concerning status indicator

After the battery has been charged, it should be used more often in order to remove deposits on the status indicator and to prevent incorrect indications (shake and turn upside down).

The battery must be checked using the charge status indicator which uses 3 different colours to indicate the condition of the battery:
•GREEN:
The battery charge is > 65%, the acid level is OK.

•BLACK:
The battery charge is < 65%, the acid level is OK. The battery should be recharged.

•YELLOW:
The acid level in the cells is below the permissible mark. The battery must be renewed.

No mention of any melting terminal boxes tho.....

On an aside it was quite handy having a 4 seater today to be able to move 3 of my colleagues around but I have to say it's a long way to Bradford and back in a 318. I've had loads of BMW's but only coupes - I didn't realise they made wallowy old boats too!
 
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