safulop

My S4 is running great. I've noticed, though, that the alternator gauge dips quite a bit below 12V when idling, especially with headlights on. It goes as low as 10V, sort of flickers like the gauge is a bit hinky. Does this indicate a problem with the alternator? Battery? This could be related to my hesitating first crank when starting?

-Sean

Alan

If its not cranking well likely its a battery problem. The battery should be able to maintain ~12v @ idle - 10v is too low. if the battery has a bad cell - it may affect charging (too much current) and cause the alternator to struggle @ idle.

Whats the voltage with ignition on, before starting?

Take the battery in and get it tested.

Alan

safulop

Ah, before starting the gauge reads 10V. This is bad, right? Sorry to be such a dweeb, my old 944 didn't have one of these newfangled alternator gauges so I kind of never learned how to use one.

-Sean

WallyP

There are a LOT of connections between the voltmeter and the battery. Resistance in those connections can cause low readings.

The voltmeter can be adjusted - which means that it can be adjusted wrong.

The first thing that I would do is to take readings with a good hand-held voltmeter. Start at the battery posts (not terminals), then on the terminals, thenon the jump start post, then on the main terminals at the top of the Central Electric Panel, etc.

safulop

OK, so the gauge is not a foolproof reading, and it does bounce a little. I will not race to change the battery while it's still running so well, I will check a few things and clean contacts first, thanks.

So can a battery be bought at my FLAPS? I bought a 944 battery at Kragen a while back, they had to order it in from a nearby supply warehouse but it was simple enough.

CharlieL

I don't believe 10 volt will turn the engine!

Mrmerlin

needs to follow Wallys advice before any wrenches are turned

Alan

10 V will certainly turn the engine, even 8v will turn most smaller engines and likely most 928 engines too (though perhaps not when very cold). However the 10v or 8v is during actual cranking - not just sat there with ignition on... I wonder what this one is putting out during cranking (quite likely about 8v...)

In this case I'd just take the battery in - seems fairly conclusive & painless, however do clean up battery & ground connectors when putting it back in - follow Wallys other advice for better performance generally, get a DVM and compare that to your dash guage reading.

928 battery size is fairly common (trucks mainly) most local places will have one in the correct case & spec.


Alan

Captain_Slow

voltmeter in my 86.5 did some of the same things, bounced around a bit and also frequently below 12V, closer to 10V. However, readings with a multimeter at the battery while engine was running revealed 12 to 13V at the battery posts. The pod voltmeter is often incorrect. All the gauges are rebuilt now, so no more low readings.