Diesel Alternator Woes by anvilman

Hi, being a newbee to this site I am hoping that someone has the knowledge to help. I currently have two 75 diesels (1 x Manual & 1 Auto) plus a Mk2 ZT (don't ask why I have three of the things as my neighbours already think I have a home for old Rovers). Whilst preparing the manual 75 for sale (I have had it standing on my drive for close to two years and need the space now!) I started it from cold and after about 30 seconds noticed a burning smell and then smoke coming from the back of the alternator (where the plug fits). Bearing in mind that over the last few days I have run the car with no probs I was somewhat upset as it was due to be put on ebay sunday night!!! Accepting the car does not want me to sell it, I decided to try and fault the issue by taking readings from the three cars I have and surprise they are all different :cry:

I have taken meter readings and wondered if anyone else can shed some light on this as it may not be the alternator at fault as I decided to check the central drain plug and removed the ECU (Engine Control Unit) plastic box and wondered if something could have been upset in doing this (I was careful when I put it back)

Taking readings to earth from the two connectors in the lead(plug end) they are as follows:

Outer pin to Earth: 5.4KOhms (at the point is shows 200)
Central Pin to earth: 3.50KOhms (the point being '20')
Across the pins: 3.5kOhm

I found that reversing the leads made no difference.

Alternator readings:

Outer Pin to earth: out of range
Central Pin to earth: 2.96KOhms(again the point being '20')
Across the pins: 1019KOhms

Reversing the leads showed different results:
Outer to earth: 1024KOhms
Centrai to earth: 2.96k
across pair: out of range (diode in line perhaps?)

The Auto diesel has different reading and I wonder if it shows a problem with the manual (above) readings anywhere?

Central to earth: 11.51Kohms
Outer to earth: 5.2kohms
across pins: 11.52Kohms

reversed leads:
central to earth: 7.42kOhms
outer to earth: 5.2kOhms
across pins: 7.43kOhms

Outer to earth: out of range
central to earth: 3.27
across pins: out of range

swapping leads
Outer to earth: 1059Kohms
Central to earth: 3.27KOhms
across pins: out of range

Am a little confused with the across pins readings as it shows a reading for a blip but then goes to out of range on my meter.

If anyone can advise on this issue as I do not want to take the thing off the 75 unless I have to as reading online it seems to be a pig of a job.

Cheers, Jim

Posted 14 Mar 2012, 12:54 #1 

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Showing a reading for a 'blip' is probably you charging up a capacitor. You are measuring the regulator which has semiconductors in so the meanings will probably be odd. The readings are only slightly different, except for 1019kohms which could even be you touching the pins with your hands.

The usual fault with the diesel alternator is oil getting into the brush box and causeing the brushes to stick. However I've never heard of smoke when this happens. If it's a failed diaode in the rectifier you would only be able to check this with the alternator out, though an output voltage test might show a problem.

Posted 14 Mar 2012, 13:06 #2 

Hi Duncan,

thanks for the quick reply. I did wonder about the capacitor issue or some kind of rectifier causing that blip. I was careful not to touch the contacts and had plastic covered crocodile clips so am sure I was not making part of the readings ;-) I just found it odd that until after I had removed the ECU container to check underneath for blockages I had not had any problems with the alternator or car and am just thinking it is bad luck I guess on the timing. It looks like I am going to have to remove the thing then to test it. I do have the Auto one I could put on (unless they are different specs) but did not want to risk that if there is a wiring issue in the car? ZT just gone into body shop to have its back end sorted (I got it as a Cat'D last year) and was hoping to have the 75 listed and maybe sold. Never mind. Jim

Posted 14 Mar 2012, 13:16 #3 

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I'll have a look at the circuits this evening, but I don't expect anything from the alternator to be connected under there.

Posted 14 Mar 2012, 13:48 #4 

Many thanks. I was just looking at another post regarding the problems with the Auto box on the diesel as the one I got from a breakers has a problem when it changes from 3rd to 4th in that it tried to change gear, slips and revs up quite high then seems to manage to go into the next gear fine. Its as thought 4th is slipping. Looking at a guide on the meter readings for the solenoids and then looking at the readings I am gettings when testing I am wondering if I have reading for a petrol auto model as mine make no sense at all. eg:

1 & 2 supposed to be 513-637 Ohms and on my meter it says its 127K
18 & 9 supposed to be 14 to 18 ohms and on my meter it says 23 (I am assuming I am reading it properly as it is on auto mode and puts a point after the 23 with a '20' below it which I am assuming it means the reading is 23 Ohms? or am I being a muppet!)
If you know of another guide or the proper readings I would appreciate any help. I have already sourced a spare auto box via ebay and will change the whole thing over if I have to but if its simply a solenoid problem then I will repair the existing one and sell on the auto box.

Then all I have to do is decide which one to keep. The Blue auto connie or BRG-2 ZT choices choices.

Posted 14 Mar 2012, 14:03 #5 

Should you need to remove the alternator then it will come out from below but you do need to unbolt the a/c bracket.

Allow about 3 - 4 hours unless you have a car lift in which case it will be a great deal easier.

A recon alternator about £150 to £170!

That apart Mrs Lincoln, did you enjoy the play


Posted 14 Mar 2012, 16:56 #6 

Fingers crossed I do not need a replacement Alternator but I am not keeping my hopes up. having three and possible a forth (2ltr V6 Club SE) if it comes in to a mates garage who does not want the 75 is keeping me busy especially as I only ever wanted one of the things ;-)

Posted 14 Mar 2012, 20:03 #7 

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OK. There IS a wire from the alternator to the ECM in the plenum. It's called a 'charge signal' wire. Whether it's the alternator telling the ECM it's charging, or the ECM allowing the alternator to charge it doesn't say.

It's a blue wire, quite thin. I'm still not sure it's that, but worth checking you haven't trapped it against earth when you moved the ECM.

Posted 14 Mar 2012, 20:36 #8 

Thanks Duncan, I will take a look later on today and see if I if has been trapped. Thanks for looking for this. Jim

Posted 15 Mar 2012, 10:01 #9