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brit vw boy · Joined: 18 Feb 2005 Posts: 59 Location: oxford, england

I changed my AAV on saturday.

And now the engine runs away a little, so i will get a Tune up.

Next, i notice a strange hissing noise when i park up (after 30mins driving).
Lift the hood, its the battery hissing. Its warm too.
So I start up the engine. On tickover its charging the battery at 13.5 volts. Fine.

Then the Engine note changes slightly, the idle drops a little (only 100rpm) and the battery is now charging at 17.50volts !

The voltmeter in the car is right off the dial and its confirmed 17.50v with a digital multimeter across the battery terminals.

Anyone help out on this ??

I have got a regulator ordered .......
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1959 vw type 2
1986 Porsche 924 S
1981 porsche 924 fh lux - FOR SALE

Smoothie · Posted: Mon Mar 07, 2005 6:52 am Post subject:

I did some bench testing with a spare alternator here a few months ago - http://www.924board.org/viewtopic.php?t=13272&postdays=0&postorder=asc&start=24 ...mentioned because a bad battery, bad battery connection or no battery can cause (or allow) the voltage to spike upward even if the regulator is good. Your problem could very well be with the voltage regulator, but given the symptoms as well as the possibility that some damage has occured to it, the battery should get some attention too. Also verify that the wiring's good, including the small gauge exciter wire to D+.

Water in the connections (or in the alternator or voltage regulator) can also cause "unpredictable results". I got some voltage spikes after washing my engine last year. The problem cleared up after I found water in a connector and dried it - that was with a non-OE alternator (Delco), but I'm sure it could happen with other brands.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

brit vw boy · Joined: 18 Feb 2005 Posts: 59 Location: oxford, england

hey smoothie,
thanks for that info, it will help me big time.

_________________
1959 vw type 2
1986 Porsche 924 S
1981 porsche 924 fh lux - FOR SALE

Smoothie · Posted: Tue Mar 08, 2005 2:28 am Post subject:

I hope it does.

Yeah I found a few interesting things from that testing, most notably that a battery in good condition has to be in circuit - otherwise the voltage can almost double. Obviously it's needed for more than just starting and as a component of the charging circuit it seems to function as a very large capacitor.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

brit vw boy · Joined: 18 Feb 2005 Posts: 59 Location: oxford, england