924Board.org

[staticsan]

I have a bad feeling I'm in for some more Things To Fix On The Car.

Basically, my voltage gauge rarely reads above 12v and will dip as low as 11.5v when idling with the headlights on. This is also the time the battery/alternator warning light starts glowing faintly. I found some posts here that suggest this is normal. I haven't been organised enough to put a meter on the battery terminals yet (maybe tonight), so I really don't know what the actual voltage is like there.

It always turns over easily, so the current capacity is definitely there. I dunno how old the battery is, but I haven't replaced it since I bought the car more than 2 years ago. Maybe that would be a good idea. There's no stereo currently fitted, so that can't draw excess current, either.

Could the gauge be merely wrong? Or is it more likely some wire somewhere is a bit old and lowering what it's reading?

Wade.

[Peter_in_AU]

A quick scan of the current-flow diagram will show you that the voltage gauge doesn't measure the battery voltage but the voltage in the rats nest of wires behind the gauges.

On my old `79 there was a drop of around 1v between the actual battery voltage and the voltage at the gauge. Use a meter to be sure.

Cleaning up the wiring behind the gauges should get you a better reading
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

[emoore924]

If you're not sure, put a voltmeter on the battery when the car is running and you'll see the difference between the gauge and the actual battery voltage. The difference, if any, should remain pretty constant so you'll be able to tell what the battery voltage is.

My n/a is pretty accurate, maybe within 1/2 volt or so. The turbo shows about -2 volts (that'll pucker you up when you flip on the headlights 100 miles from home )

Bottom line: My experience says the gauge is probably accurate, but it just isn't measuring what you want it to measure...

[staticsan]

Okay, I got out my multimeter last night and when probing. It seems like there is about one volt lost between the battery and the wiring in the dash. That means the charging voltage at idle with no lights on is just over 13V. This might be a mite low, but not as much to worry about as I had originally thought.

I think a new battery might be in order in the coming months. And I need to verify the wiring to the alternator.

Wade.

[Ozzie]

I fitted a large earth direct to the alternator (35mm) and also ran a 10mm +ve.
Volt gauge reads very accurate now.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[Peter_in_AU]

I'd give a big vote for a new battery. There's nothing like a blast from a fresh battery to get a 924 out of bed on a cold morning.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

[musicalannette]

A new battery always makes a difference to your car, a bit like new tyres, but I agree with ozzie, volts drop can give you a bit of a false reading, personally I wouldnt trust the guages to be that precise anyway, there best to be used as an indicator, if the guage isnt where it normally sits then something has changed. I mean, is you oil pressure really 6 bar? The voltmeter will probably be the best after the clock, but trust your multimeter reading on your battery with lights on, heating fan set to full, your rear fogs on and your heated rear screen on. make sure the engine isn't so loaded so the alternator isn't spinning quick enough. i.e. tickover is below about 800rpm. when its like this and revved to say 1500rpm you should be getting around 13.8volts or better at the battery, then check your reading on the dash, it will give you an idea of volts drop to the gauge.

hope this helps, it might save you the price of a new battery, if not you might find a cheap new one from agricultural stockests (well there certainly cheaper from there in the uk).
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I KNEW white wall tyres were invented by Americans .....just not at Boeing.... to be fitted on the 737.....

[staticsan]

Compared with what's been spent on it already, a new battery isn't a big expense.

The other thing I realized when I looked at the wiring diagram, is that I think there's a missing wire, too. A PO had replaced the starter motor, and for some reason added an extra relay in that circuit. They did this by cannabilising one of the wires that go from the alternator to the starter. :-/ I bet if I put that back the charging voltage will improve.

Wade.

[bear924]

Hello Wade,

I your alternator light is lighting up while you are driving there is something wrong with your charging circuit. The light indicates that current is flowing from your battery instead of to your battery (from alternator). My experience is that you can drive for a long time like this however slowly your battery will discharge ... often wrecking battery due to starting car with flattish battery.

Light can be caused by a loose alternator belt (this recently happened to me) or a wiring issue (possibly faulty regulator however it wouldn't be my first guess). Grab a multimeter, put it on volts and start your car. If you don't have about 12-13V across your battery terminals you have a problem.

[staticsan]

The alternator light only glows dimly (dimly, I say) when idling with the headlights on. Take off and it stops glowing. Idling with no lights I read 13v on the battery with my multi-meter.

And this morning whilst driving it to church I noticed the gauge read 13V most of the journey, which means I probably had 14v on the battery. It sounds like my regulator is just fine.

Wade.

[musicalannette]

What is your tickover like? the 924 has a very high standard tickover at 950 rpm. just a thought.
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I KNEW white wall tyres were invented by Americans .....just not at Boeing.... to be fitted on the 737.....

[staticsan]

It's low, somewhere around 600.

It went down when I backed off the mixture so it would pass emissions tests. I've been meaning to raise the idle speed. I did fiddle with the screw on the throttle bodhy once, but nothing changed, so either I was moving the wrong screw or not moving it far enough. (It is on the side of the throttle body, isn't it, towards the front of the car?)

Wade.

[musicalannette]

its right at the top of the engine on the plennum chamber, a slotted screw with a locknut, just losten the locknut first (its easiest stood from the left of the car) and adjust with a flatblade.
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I KNEW white wall tyres were invented by Americans .....just not at Boeing.... to be fitted on the 737.....

[Ozzie]