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VT V8 charging problems

terrible one

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Hey guys

I have this ongoing problem with my VT 5 litre.

In the morning car starts ok. After about 5-10 minutes of driving charge rate drops to 11.9V. I replaced the alternator with a new Bosch unit and fitted a new Bosch 530CCA battery. Still no good. I heard they had problems burning out battery harnesses between battery and alternator. I ran a new thick cable from battery to alternator and still no good. I checked, cleaned and tightened all visible earths off battery -ve terminal and still no good. When cruising charge rate is around 13.5V. If allowed to idle for a couple minutes with slowly drop down to 11.9-12V again. This is with a brand new alternator.

What the hell is going on?! Is my external battery cable not good enough, do I need to replace the actual harness?

Does the engine have an earth strap around the back that goes to the body somewhere? I looked but couldnt find it, its the only one I havent checked and cleaned.

Thanks

Nick
 

scozz76

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Check your earthing.

The alternator volts will be lower at Idle

What are you using to check the voltage? I would not trust the reading from a cheap multimeter (some head units have voltage displays..... I wouldn't trust them 100%).
What happens when you put the battery under load? (lights on, A/C on etc)

You may find the alternator is ok.
 

terrible one

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Im using the voltmeter on the dashboard, it gives the same reading as a Fluke multimeter so I know its correct. Is it worth running an earth from the body of the alternator to the -ve of the battery or directly to the block or body?

Does the engine have any other earths apart from the one that runs directly from the -ve battery terminal to the power steering pump bracket? I've looked around but cant find one. I know V6 Commodores have a earth on the back of one of the cylinder heads but cant find a similar one on my 5 litre.

Thanks
 

nasty1

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Interesting. I'm having an issue in my Vl similar it just over 12v with no accessories running. I replaced alternator and ran new 4gauge wire to alternator and Stil same
 

veewye

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terrible one, check the voltage at the rear of the alternator with your multimeter if the reading is around the 13-14v it is suffering from voltage drop or a bad earth
 
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