VZ 6.0 Litre V8 Faulty Alternator/PCM mystery!!!

[Mapleston]

Hello Everyone.

I really need the advice of the most knowledgable VZ commodore experts out there!

I bought a VZ commodore 6.0 litre with 150,000 on the clock.

An issue soon reared its head where I was getting all the dash lights, aircon, radio & clock turning off for a few seconds when driving. I also found that If I turned my high beams on during the time that this happened (when everything in the cabin was off) it immediately blew the bulbs!

I checked all the earth connections etc.

The next thing that happened was my alternator started to charge intermittently. I checked voltage to the battery and it was 11.80 odd volts, then sometimes I could hear the alternator working I checked the battery voltage and it was 14+ volts.

This has been happening intermittently with the alternator charging less and less.

So I pulled the alternator out and opened it up, the brushes are good, everything looked fine although I don't know how to check anything else on the alternator.

I realise that the regulator is computer controlled.

So am I on the right track? a new alternator costs a lot, I don't want to by a new one if its a PCM issue or is it an ABS module issue?

Please give me any little bit of advice you might have as I am interested to understand actually how this all works as well as wanting to fix the problem.

Thanks in advance.

 

[mpower]

voltage spikes? sounds like the regulator is stuffed.

 

[Adder]

Here's a wiring diagram of the starting & charging circuit

WP 20140625 003

Hope this helps

 

[MYVESSV8]

failed diode on the rectifier plate, diodes only pass current/voltage in one direction when testing them, but it is how they form a bridge to change the Alternator output from ac to dc

 

[petern64]

exact thing happened to me , it was the alternator !

 

[Mapleston]

Thanks, I came to the conclusion it must be the alternator as every mechanic I spoke to said they have only ever had the alternator be the root of the problem...I even paid a mechanic $20 to test it and then have them tell me they couldn't test it as it is PCM controlled or something.. and still made me pay!


The mechanics all wanted $700.00 - $1100 for a new alternator.. I took the risk and bought a newbie on ebay for $285.00 - genuine article thankfully, put it in and so far so good. Charging well and no unusual lights or sounds yet....

thanks for everyone's input - much appreciated.

 

[GRUMBLA]

Hey mate. I've got a Vz clubsport. And having dramas with. Over charging. I've been told about the pcm regulating the voltage the alternator puts out. Did abit of research and came across this. Mine did the exact same thing,the entire dash dropped out no lights or gauges etc. and had the abs light flash of the screen. It's is also a new alternator about 4 weeks old. And the battery is new because the old one died after the dash dropped out. I connected a g-scan tool and went into read all the parameters. And the control module got Upto reading 17volt. And I shut it off. Have you had any dramas since you hav replaced your alternator?? Also the reason I replaced my alternator in the first place is because it was dropping charge. And dropping out completely. Then 4 weeks later it is doing this. I removed it and took it bak to where I got it. All car bitz. And they then told me about The PCM had the regulator. In it. I spoke to a auto electrician and he confirmed that the Vz's do have the reg in the PCM. He told me about using the scan tool to check the out put. I just can't afford to waste the money on a new pcm if it's a faulty alternator

 

[Mapleston]

Hello, after i replaced the alternator i have had absolutely no issues. Other than that, i can't really offer much advice. Have you checked that everything is earthed well? I have also heard said that sometimes the pulleys on the front of the alternators give issues. (if its the one with the clutch system in it). Sorry can't help much.

 

[MYVESSV8]

Bit rude taking ya money, but with the car running if you put a multimeter across your battery and its charging (approx 14.4v newer systems are slightly different)as a guide no issue, with the car turned off a charged battery will read about 12.8v (generally speaking)
the pcm is only regulating the input to the field to vary the voltage output

Thanks, I came to the conclusion it must be the alternator as every mechanic I spoke to said they have only ever had the alternator be the root of the problem...I even paid a mechanic $20 to test it and then have them tell me they couldn't test it as it is PCM controlled or something.. and still made me pay!


The mechanics all wanted $700.00 - $1100 for a new alternator.. I took the risk and bought a newbie on ebay for $285.00 - genuine article thankfully, put it in and so far so good. Charging well and no unusual lights or sounds yet....

thanks for everyone's input - much appreciated.

 

[GRUMBLA]

Hey mate. So are you saying that the pcm. Is the cause for the alternator putting out 17volt+. And what do you mean by input to the field ?? Thanks