924Board.org

[5150]

Okay, so here's the history:
Alternator has never put out a particularly good charge, for ages it was erratically stopping charging completely then kicking back in. In February I put a new starter in but soon after took the car off the road when the test ran out.

Got the car down for it's test and noticed the voltmeter was barely moving, it was sat on the bottom of the green and slowly dropping, blipping the throttle would make it move slightly.

Couldn't *see* any issues, no loose wires, belt was tight etc.

So, I popped for a new alternator yesterday, didn't mind since the old one was re-con'd at a local place years back and never seems to have been right since. Put the new one in last night and..... it's no bloody different :-/ the car struggles to run, voltmeter well below the green and only slight movement if you pop the throttle.

So, my thinking - the starter is getting plenty of power so the initial + wiring from battery to starter must be okay. This leaves either the bridging + wire from starter to alternator AND/OR the - earth strap from block to alternator casing. This sound right to you guys? I've got the starter and alternator both out so I can see all the wires clearly, nothing looks at all out of the ordinary...
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Mars Red '78 Euro 924 n/a
http://www.cardomain.com/id/5150_uk

Graphite? Grey Metallic '85 (late model) 944 2.5

There are two kinds of pedestrians: the quick and the dead.

[Meneer aard]

In my 924 (77, euro) the volt meter gives wrong results, when I started the car it gives arround 13,4 volts. But when I drive, the volt meter drops arround 12,5 V. When I read the battery with an volt meter (external volt meter) it gives 13,6 with an idle engine (1000 rpm).

Make sure that your ground cables are clean and tight. You can use a thick cable from the alternator earth to the battery earth or to the engine or somewhere else.
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Porsche 924 Euro 1977

[5150]

I've picked up a couple of new quality leads to replace the earth and the positive. With the engine suddenly running like crap it's definately not getting enough juice through so hopefully these will resolve it...
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Mars Red '78 Euro 924 n/a
http://www.cardomain.com/id/5150_uk

Graphite? Grey Metallic '85 (late model) 944 2.5

There are two kinds of pedestrians: the quick and the dead.

[leadfoot]

The starter will have nothing to do with the good running of the engine, that's essentially the alternators job sarters just do as they say be it with a little extra boost in power from the alternator... it just shares the same power strap to the battery so this needs to be assured of a good connection of the right gauge wire.
What you waant to aim for is minimal drop in voltage between the alternator and battery. To test for this place your positive probe at the alternator and negative at the battery and measure the volts, should be less than half a volt, anything more and you should test the ground strap of the alternator for voltage drop too (a good idea anyway to do this and also run a secondary ground strap)
If you start your car with a voltmeter across the terminals of the battery this should give you an indication of whether the alternator working properly as charge will jump from 12/13volt to around 14.5 volts, anything higher and the regulator is shot.
Make sure your battery is holding charge overnight, otherwise you need to test the acid levels and the specific gravity of each cell.
Hope this helps
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...