Battery/alternator problem

[TheMoleKing]

The car is a 1990 GT2.

So my battery didn't start this morning so I called my friend to jump start it. Couldn't get the car started that way, so we changed our batteries over to see if it would work with his.

Hey presto it starts... however the battery was disconnected with the car running and the engine died.

I'm pretty sure this means my alternator is buggered? Is this the case?

If so, I've put my reg number into CarParts4Less and it comes up with loads of options for alternators, so I guess my other question is exactly what are my best options if I do need a new alternator?

Thanks!

[Jack92]

Doesn't always necessary mean it's dead but the majority of the time yes your right it does. However I would first check with a multimeter just to be sure.

As for the alternator what are the variants between them?
As it could be as little as the make which wouldn't effect if it works or not could just prove more reliable.

As long as the ampage and rough size and mounting holes are the same you should be fine

[ianaudia4]

The Sciroccos came with a variety of amperage alternators during its build life, these ranged from 45 amp up to 90 amp, the biggest difference (except the amperage) is the wiring, some had plugs and others had O-ring connectors. As long as you get an alternator that is higher rated than your battery you should be okay.

Before searching though check your earth strap to your alternator.

[Nate]

If you put the jump leads both onto your (flat) battery and it made no difference, that would point to the wiring - either the earth or the big +ve cable are most likely - not getting power to the engine.

Don't buy an alternator until you have done a bit of testing, as I suspect you will be wasting your money.

with the car running, you need to take a few voltage readings. Very simple to do with a relatively cheap multimeter. If you have a search, you will find my previous posts on how to test battery cables and alternator charge rates.

Make sure the earth cable is tight, and the bodywork and gearbox clean where it bolts on.

Moe sure battery terminals are clean and tight, then put a thin smear of petroleum jelly (vaseline) on them to keep any corrosion away

[TheMoleKing]

Will do thanks Ian, I'm going to perform a thorough investigation tomorrow.

So I've charged my battery at my work, now if put it back, start the car and I stick a multimeter on the battery and I'm not getting more than 12V then there's going to be an issue with the alternator.

Then if I check the alternators earth strap, make sure there's nothing wrong with the rest of the wiring.

Does this sound sensible?

Also -- would it be worth first replacing the Alternator Voltage Regulator as these are fairly cheap?

Thanks for the help, electronics is not my forte!

[ianaudia4]

To check if the alternator is working use a multimeter, put the red coloured probe onto the live on the alternator (pull back the rubber cover) and the black probe on an earth point. Make sure the range on the multimeter is up to 20v DC, if the alternator is working it should read somewhere between 13.7 and 14V ish!

[TheMoleKing]

Thanks Ian/Nate!

I shall report back on my findings I'm sure :)

[Nate]

Read this : http://www.sciroccoregisterforum.co.uk/ ... ery#p31755

[TheMoleKing]

Legend, thanks. Did a search earlier but didn't find that post!

[TheMoleKing]

Okay so I've done some testing, voltage across alternator is 14.1V, and voltage across battery is 14.06V, so not much loss there, and looks like the alternator is working fine!

I also checked the voltage across the -ve terminal and the alternator case, nothing there, and nothing across the alternator and +ve terminal.

So assuming that the alternator is okay, I'm going to have the battery tested , if the battery is fine maybe I should change the alternator voltage regulator?

Could there be any other reason why when the battery was disconnected the engine cut out, and why the battery was dead in the first place?

[Nate]

An engine will often cut out when you take the battery off, even though theoretically the alternator should generate power to keep it runnning.

For future reference, removing the battery when the engine is running is generally considered a bad idea. Upsets the alternator, and the big power spike when you reconnect a flat battery can toast electronics

[TheMoleKing]

Yes it wasn't intentional on my part, my boss was moving the jump leads after we'd swapped batteries and it cut out as he accidentally disconnected the battery!

Anyhow, I went and got the battery tested at Halfords as it's round the corner, and free, and the chap said it look find... I'll have to see how it goes then I guess!

[Nate]

Only a wild guess, but is your radio only wired to a permenant feed? Quite a few don't actually turn off when you turn them off. Think standby mode

[mark1gls]

How old is your battery and does it have a guarantee with it, could be the battery is starting to come to the end of its life and its letting you know before it dies completely.
Check the boot light is not staying on?

I brought a Bosch battery (063) with a 4 year guarantee for £40 with free delivery to my door from the Euro car parts shop on eaby a couple of months ago.

[TheMoleKing]

Only a wild guess, but is your radio only wired to a permenant feed? Quite a few don't actually turn off when you turn them off. Think standby mode

Bingo, you might be onto a winner here, this also crossed my mind last night. What's the easiest alternative, splicing from the switched live that goes to the heaters?

And the boot courtesy light also struck my mind, as I wouldn't know if it was still on when I shut the car.