Battery or alternator?

[BRE-240Z]

I'm having an electrical problem, and I hope someone can point me in the right direction or give me some better troubleshooting tips than what I currently have in my toolbox.

I have a reasonably stock 240Z, with an upgraded alternator (ZSpecialties 105 amp, internally regulated). I drove my car to work on Thursday, and then used her to run a few assorted errands (I figure I put sixty miles or so on the car that day). That evening, I took her out again, and she started running very rough and the gauges started jumping all over the place. I finally babied her off the road (luckily I was on a downhill at the time), and after finally dying....she refused to start.

I tried to start her back up, and got an 'Rrrrrt. Click, click'. Then nothing.

So at the time, I was thinking that it was the battery that was the problem. A friend came by, and we were able to charge the battery and get the car home. The battery is old and I have no faith in it, but I'm starting to put together a nice little history of bad batteries in the brief time that I've had this car running, and I'm not entirely convinced that the battery is the problem.

So today I got the car started (surprised me that she would even fire up, after sitting in the driveway for a couple of days). I let her run for a bit, and then measured the voltage at the battery for a minute or two (it was holding pretty much steady at 11.5 or so, which seems low). Then I pulled the positive cable off of the battery, and the car died immediately.

Doesn't this indicate a bad alternator? This alternator is pretty new, I mean it has maybe 100 miles on it, total, since installation. Is there another test that I can do to verify that the alternator is the problem? Is the possibly flaky battery contributing to the problem?

Any help would be appreciated. Thanks, guys.

[280~Master]

Yes this should be an alternator problem, Double check all of your grounds and make sure your wires are clean and tightened.

[sblake01]

Then I pulled the positive cable off of the battery, and the car died immediately.

Don't do that! I know it's an age old trick but you're just asking for more problems when you do that. Especially if you put it back on while the car is still running. There is an alternator test procedure in the the FSM.

[westpak]

as mentioned it sounds like an alternator

if you can get the car started and running the battery is just along for the ride and getting recharged from then on.

pulling the cable from the battery, not wise as mentioned, and the car died just shows that the car was running off the battery and not the alternator, you can run that way for a while until the battery discharges and you no longer have juice to run the electrical

Testing at the battery was probably just telling you how much voltage the battery had if the alternator was not working properly, best way to check alternator is to use the voltmeter on the power post of the alternator and ground or alternator case, if that is less than 13-14 then your alternator is going bad.

[V8-240Z]

I pulled the positive cable off of the battery, and the car died immediately.

.

Thats a trick when the cars had generators but it could ruin the alternator.

A safer trick is to hold a screw driver at the rear bearing with the engine

running, but don't touch any wires!!! If the alternator is working there will

be a strong magnetic attraction that will pull the screw driver. If it is not

working there will be nothing.

[EScanlon]

Thats a trick when the cars had generators but it could ruin the alternator.

A safer trick is to hold a screw driver at the rear bearing with the engine running, but don't touch any wires!!! If the alternator is working there will be a strong magnetic attraction that will pull the screw driver. If it is not working there will be nothing.

Excellent! That one tip is gold.

I'll have to go try it!

E

[V8-240Z]

Excellent! That one tip is gold.

I'll have to go try it!

E

I have been using that trick for years, it even will magnetize the

end of a screw driver or piece of metal so you can pick up hard

to reach parts.

[biddljj]

This web site should have a Golden Tips Sections...... This alternator clue is a great one...

Thanks, Zdisease

[sblake01]

That trick works and I'll admit that I've used it quite a few times but it also has margin for error. e.g.:

but don't touch any wires!!!

Much safer to use a voltmeter with the positive probe on the the 'B' terminal and the negative probe on the 'E' terminal on the alternator and read it while the car is running with the high beams on. Under 12.5 volts, no good. Over 12.5 volts at idle and over 14 volts at 2400 rpm, good.