When Alternator Goes Bad

[SuperSpartan]

Im sorta confused i have a thing that tells me the voltage and sometimes it wont start i cant tell if its the battery or the alternator?
any ideas how to test them?

[jchaske]

Originally Posted by SuperSpartan

Im sorta confused i have a thing that tells me the voltage and sometimes it wont start i cant tell if its the battery or the alternator?
any ideas how to test them?

Just got a 87 nonturbo, before that worked on american classics, but to test the alternator I would simply pull the negative battery connection while the car is running, if it dies out immediately the alternator is not providing the charge, the battery is, hope this helps!

[SuperSpartan]

YEAH! i did it thanks alot
battery is weak
alternator works great

[MA70-3.0GT]

Originally Posted by jchaske

Just got a 87 nonturbo, before that worked on american classics, but to test the alternator I would simply pull the negative battery connection while the car is running, if it dies out immediately the alternator is not providing the charge, the battery is, hope this helps!

Not to rubbish that idea as it's fine on older stuff without electronics (indeed I've started many older cars with a good battery before removing that one & putting the flat one back in to charge, whilst it's running), but as soon as you start doing that on vehicles with ECU's, EFI and other electronic circuits (and we all know the Japanese especially LOVE electronic goodies!), you run the risk of damaging any number of components from a coil right through to the main ECU by creating a voltage spike as you remove the battery lead. (the alternator's kicking out the current to run the car & charge the battery, all of a sudden the load of charging the battery disappears & in the split second before the regulator can catch up *Bang*, there goes all the electronics that were switched on at the time...)

Avoiding voltage spikes can also apply to jump starting from another car, always make sure you connect the neg/- lead to the dead car last & disconnect it first & never hook it to the battery - post on the dead vehicle, always to a good earth like an engine mount or piece of the block/head. Like I say, not rubbishing the idea & it's fine on older stuff, just not these...

[yuyo]

wow 17 years really a hardcore...

[MA70-3.0GT]

Still waiting on mine to go, 135k & nearly 20 years!!! (has stood at least 4 too).

Guess it's not as healthy as it could be but still charging, just...

EDIT-: I shouldn't have posted here, I knew it!!! So literally the day after making this post as I'm driving the car the 2.5 miles or so home after collecting it, I switch the blower on to clear the screen & the car nearly dies till I (rapidly!) switched the blower off again, get home & the previously freshly charged battery is at 8.76 volts... lucky me.

EDIT #2-: so while the engine's in bits for the HG job I stripped the back off the alternator & the slip rings aren't too bad, brushes were dead though. I've just cleaned up the contact surfaces & stretched the springs for now to see if it works when she's all back together. If it does then I'll try to find a brushbox for the right money before spending out on a recon.