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jayrc
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1994 Vauxhall Astra - Electrical Problem

03/08/2010 2:12 PM

I have a 1994 Vauxhall Astra which despite being well past the UK government's 'scrap by' date has only done 73,000 miles and is a clean and normally reliable car.

This morning it developed a fault however. Whenever I go much past 30 mph the alternator warning light starts flickering. More worrying still is the fact that at 45 mph the air bag warning light flashes and stays on steadily at 50 mph.

My first thought was the alternator drive belt but that seems reasonably tight and there is no sign of overheating (the same belt drives the water pump). Any ideas? I have most tools including a voltmeter but no idea of what voltage I should expect from the alternator.
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lyn
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#1

Re: Vauxhall Astra electrical problem

03/08/2010 3:11 PM

Assuming it's a 12 V system the alternator should produce about 14.5V at a fast idle.

Check the belt tension! Don't guess. If you can deflect the longest belt span more than the thickness of the belt with moderate finger pressure make it tighter.

If you just drive around town, the battery may just be undercharged.
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JohnDG
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#2

Re: 1994 Vauxhall Astra - Electrical Problem

03/08/2010 7:20 PM

Does the warning light flicker start at a correspondingly lower speed in third gear? (i.e. is it directly related to engine rpm?). Can you reproduce it by (gently!) revving the engine to about the same rpm in neutral at a standstill?

Just to get things crystal clear.

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jayrc
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#3
In reply to #2

Re: 1994 Vauxhall Astra - Electrical Problem

03/08/2010 8:03 PM

Yes - it's directly related to engine speed. The info I gave was when running in 5th gear.
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Beej50
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#5
In reply to #3

Re: 1994 Vauxhall Astra - Electrical Problem

03/08/2010 11:20 PM

VAUXHALL ASTRA?

1994????

SORRY!

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Yosemit3
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#4

Re: 1994 Vauxhall Astra - Electrical Problem

03/08/2010 11:20 PM

typically worn brushes in the alternator. the braided wire connections doesn't allow them to contact the slip rings with enough force to conduct the necessary power.

the airbag light is a response to the alternator fault.

it is best to go to an electrical specialist, who can diagnose, and rebuild your unit, rather than the chinese import exchange unit.
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Andy Germany
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#9
In reply to #4

Re: 1994 Vauxhall Astra - Electrical Problem

03/09/2010 3:44 PM

I gave you a GA, but I would guess that with new brushes, everything starts to work fine.....

The electrical "noise" of worn brushes can bring many different faults....

Change them before a diode is damaged....

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Philo
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#6

Re: 1994 Vauxhall Astra - Electrical Problem

03/09/2010 12:47 AM

Worn out alternator by the sound of it - should be easy to source a replacement from scrappy for less than £50, lots of Vauxhalls had essentially the same unit (Nova, Corsa, Cavalier, Carlton, Omega).

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jayrc
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#7
In reply to #6

Re: 1994 Vauxhall Astra - Electrical Problem

03/09/2010 11:28 AM

I measured the voltage at the battery. At tick-over it's 13.6 volts. Reving the engine produces 16.5 volts and the alternator light comes on!
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JohnDG
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#8
In reply to #7

Re: 1994 Vauxhall Astra - Electrical Problem

03/09/2010 11:42 AM

The battery voltage shouldn't go over about 14½ volts - sounds like the regulator's nackered.

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lyn
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#10
In reply to #7

Re: 1994 Vauxhall Astra - Electrical Problem

03/09/2010 4:40 PM

So, I'm out of my league here but I do have one more thing. When it's running at 16.5V what happens if you turn on all the lights, heater fan etc. That should pull the voltage down and the light should go off???

I don't know. Good luck.
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bhrescobar
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#11
In reply to #7

Re: 1994 Vauxhall Astra - Electrical Problem

03/09/2010 8:00 PM

Yep, agree. Worn regulator. A change in electrical load will typically cause a deep change in the tension, because the regulator itself is keeping voltage down at iddle as he mentioned. Relax. Take it to someone replace it for you, or replace all the alternator by a reconditioned full unit if available and prices are reasonable. Just because in this age, brushes and bearings may also be facing their reliability edge. Unfortunately, nothing last forever. And be quick. Do not allow more things to burn because of this tension variation. You should be able to buy some new parts at reasonable prices from the GM line as told here before. They are all the same.

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Andy Germany (1); Beej50 (1); bhrescobar (1); jayrc (2); JohnDG (2); lyn (2); Philo (1); Yosemit3 (1)

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