What's the best way to test alternator without removing it?

[Cgeigert]

My car has been having some trouble that I think is related to the alternator but I don't want to remove it if I don't have to. Car was having some issues reving, and turning on lights or anything made it worse. Charged battery fully and it drove like a champ for about 30 miles. Went somewhere today to run an errand, only left car for like 15 minutes. Got in to start it to return home and it didn't have enough juice to start. Got a jump and car made it home about 5 miles with no issues then right when I got there started having the reving issues and it was losing power. Car has never actually died while running, just starts getting bad and then once you turn it off it won't have enough juice to start. So I'm thinking the alt is going bad, it doesn't make any noise, it just doesn't seem ot keep the battery charged. I read you can test terminals while running and if it's under 13V in general then alt is bad. Is there a better way to test alt at the alternator itself? What wire or pin do I use? Don't worry, I'm not going to disconnect power while car is running just want to test it without removing it.

[Hijacker]

http://www.carbasics.co.uk/How_to_test_ ... rnator.htm

[Cgeigert]

Thanks, yeah I'll do those things for testing across the terminals. I read some guy talk about how he tested it at the alternator itself but I didn't understand his explanation. Pretty sure it is the alt. Battery is 6 months old and has 700cca. It's relocated to the back but I checked where all the positives were bolted together. I have two grounds from battery, one to the side of the metal and one to the rear strut bolt. All the other grounds and wiring to alternator seem good, and fuses and fusible links are good. The 75A alt fusible link was kind of loose inside when I shook it but everything was still intact. I have the silvia lights wired up along with some additional wiring like aftermarket power windows and starter button so alt was probably overrunning. Car would just slowly get crappy as battery drained, I'm used to alternators just dying and losing all power to the car.

[Cgeigert]

It appears that I had a bad battery. I had ruled that out because it was only 6 months old but it was one of those walmart ones. Replaced it with another walmart one and seems to have fixed the issue. I took some vids using the meter to diagnose it, don't know how to post them here though

[Cgeigert]

Never mind, started doing the same thing again. Gotta triple check all the wiring and if that doesn't work gonna yank the alt and test that,

[Cgeigert]

Did some more testing to make sure the alt is bad and not something else. I've read tons of threads of people with charging problems who replace their alt and nothing changes. Testing at battery and at positive output on alternator I was getting barely over 12. When I did same test on my other s13 I was getting between 13.5 and 15. So it looks like the alt is slowly going bad and barely putting out 12 volts to the battery. Pretty sure that confirms bad alt right, is there any other reason I would get a reading like that at the + output?

[Hijacker]

It is slightly low, so it could be a bad alt. As much as I hate suggesting these places, take the car to Advance or Auto Zone and have them hook up their meter. It's pretty decent at catching problematic alts.

Another thing you might have going on if you're draining batteries, is parasitic loss. Here's a handy chart with voltage drops across fuses that you can test to see if you're having an issue. There are a few older style tests that you can perform instead as well, I just don't recommend the test where you start the car and disconnect the negative terminal of your battery. That can lead to frying your ECU.

how-to-test-your-battery-alternator-and ... 43214.html

This has the "pull the negative terminal" technique.

http://flashoffroad.com/electrical/Batt ... Drain.html

This link shows a test using a multimeter to bridge the positive terminal and terminal clamp to watch for voltage drop. It's a decent test, but can be finicky.

[Cgeigert]

Thanks I'll have to check that stuff. I re-checked voltages and alt doesn't get much over 12v, and if I turn on accessories it starts going down. I'm not seeing much difference in readings between battery post and alt. + terminal. If I was having parasitic drain I would think that would drain battery while it's sitting, but there would have to be a massive arc to drain power from the car while it's driving right? Is there anything else (other than wiring) that would cause alt to not charge battery? What else is between the alt and the battery? All fuses and the 75a fusible link look good. Guess at this point I'll just have to pull the alt and see.

[Cgeigert]

Replaced alt with s14 one. Fixed problem. Seems like these alts go out slowly, not all at once.