The V8 Owners Forum -

Hi folks.

just fitted a new battery, new alternator was fitted early this year. when the engine is idling voltmeter sits at 12v and doesnt move when engine is reved up. the engine is a rover 3.5 fitted into a mk2 hilux, any body have any ideas whats up?

cheers

Is that a dash voltmeter? If so, check with a DVM across the battery. Should read 13.8 volt at a fast idle with a fully charged battery and no load other than the engine electrics.

The dash voltmeter may give an incorrect reading due to many things.

funny thing is before my old battery died, the voltmeter sometimes would show nothing, then it would jump to 14v, then nothing again.

DaveEFI wrote:Is that a dash voltmeter? If so, check with a DVM across the battery. Should read 13.8 volt at a fast idle with a fully charged battery and no load other than the engine electrics.

Chris.

shawser wrote:funny thing is before my old battery died, the voltmeter sometimes would show nothing, then it would jump to 14v, then nothing again.

Again, is this a dash meter? If so, it could be a problem with that or its wiring rather than the battery/charging circuit. Indeed, I'd say that is more likely.

I've fitted a voltmeter to my SD1 - it had only a warning light. It's in the revcounter, and at first I wired it to the rev counter supply. The readings it gave were nonsense. So it is now wired direct to the battery via an ignition controlled relay.

so if i take it off and connect it straight to the battery , if all is well then it should idle around the 12v mark and go up to around 13.8 when revving?

shawser wrote:so if i take it off and connect it straight to the battery , if all is well then it should idle around the 12v mark and go up to around 13.8 when revving?

That would depend on how accurate the voltmeter is and if it's working correctly.

A fully charged battery will read just over 12 volts with the engine stopped.
At idle (with most alternators) and only the engine electrics on, I'd expect to see 13.8. Roughly.

A DVM is a good investment if doing any electrical work. They are remarkably cheap these days. A few years ago to get that sort of accuracy would have cost a lot of money.

i took off dash volt meter and connected to battery, reads just over twelve with engine off, the same on idle. looks like i need to get a proper volt meter.

Yes, you want an instrument that you can trust.

Chris.

shawser wrote:i took off dash volt meter and connected to battery, reads just over twelve with engine off, the same on idle. looks like i need to get a proper volt meter.

Would be best.

Did the new alternator come from a reputable source? Many cheap 'reconditioned' ones are simply cleaned up used from a scrappie.

it was a brand new one from a rover dealer. trying to sus out where the thin wire goes to for charge light. see if light goes out.

shawser wrote:it was a brand new one from a rover dealer. trying to sus out where the thin wire goes to for charge light. see if light goes out.

Ah. If that's not connected, no charge. Same as if the bulb blows. It needs a tiny amount of current from the battery to start it charging, and it gets that via the warning light.

well i got a voltmeter, reading just over 12v, on idle the same. i connected thin wire to charge light on instrument cluster, started and engine wouldnt turn off with key.

Some funny sh*t going on with your alternator. The thin wire should run from the alternator to the charge light. Then the other side of the charge light should be fed from the ignition switch.

Chris.

this is doing my head in, just cant figure it out. Must be something simple.