Thread: Alternator UNDER CHARGING issues?!??!?!

So my b14 alternator starting overcharging in the mid 14 and 15 volt range. I took it out and replaced it with a b15 alternator I had in the garage and the charge value no matter the rpm was low 11 volt range. Thinking it was bad and old I bought a new alternator from autozone which seemed to be the same style as the b15 alternator. I put the autozone one in and same exact issues....subpar/low charge! Anyone have a direction they can point me in?

More info needed. Where are you taking your voltage measurements from, the output of the alternator, or at the battery?

Take a look at the image in this post, it shows the basic charging circuit. That's for a B13 but I think the B14 should be similar. The output of the alternator (the stud with a cap over it) goes directly to the battery (via a fusible link), and the battery voltage goes back to the alternator (after the fuse block) to tell the regulator in the alternator what the battery voltage is. The regulator will increase or decrease its voltage output based on what the sensed battery voltage is.

You may have a bad connection in one or more areas, that can be causing problems. I would also take those other alternators to your parts store and have them verify the output on their machine, they should be able to verify that the regulator is working and tell you what voltage it is putting out. If they test good there, you've got a wiring fault to track down.

take the alternator back to vatozone and have them check it out. Its not uncommon to have aftermarket alternators to be bad out of box.

If it checks out fine, then on to wiring. If you are getting high resistance, then you will get voltage drop as that resistance turns the energy into heat.

@jimbo_se-r , the voltage was taken at the pos. post on the alt. per the ecu, the system is seeing mid 11s for voltage.....which is the same reading I am getting from the past just about. I swapped batteries to test that theory and same result. im pretty sure it not the alt. but I am goin to have both of them tested like @zeneffect said just to make sure they are both good, and that will narrow my options down to wiring.

I know that on the B13, there is a ground wire that attaches to the alternator body, I am not sure about this wire on the B13, but apparently it was on the B13 as there is not a great ground connection to the chassis (and the battery) through the engine block, which is why some sensors on the motor have grounding issues.

Is this wire present on your setup? It may be worth adding just in case. For fun, check the voltage between the alternator housing and the chassis, see if you get more than .2v. If so, you will want to add that ground wire.

here is my thing, how can everything work correctly with 1 alt, but not 4 others?!!? this lead me to believe it cant be a system or wiring issue.

...maybe you jiggled a 20yr old wire the wrong way? Did you get the battery and the alternator tested as you indicated?

OK, first, I had a typo in my post above and it has been quoted a few times here. I had B13 three times, the middle one should have been B14.

Now, you said you have one alternator that works correctly? Which one is this? Last we read, you had one alternator over charging, and two that had low output?

Try this, check the alternator output with the car OFF, and see what your voltage is, then try again with the car running. I'm going to bet there won't be any difference if you are only seeing 11v at the output. My guess is that one of the other wires going to the alternator may be damaged. You're going to want to check the wiring chart for the B14 to help troubleshoot.

As I mentioned above, check the voltage between the alternator casing and chassis ground, or battery negative. Anything more than .2v and you want to reground the alternator. Check the 2 pin connector going to the alternator, one of the wires should show battery voltage, if you aren't seeing that, then the alternator isn't getting the voltage signal it needs to regulate output.

Get an oem unit.Andreas miko sells these used.I baught 1 alternator from him.on the car for 4 years and counting.I would also check your alternator harness.move it around to see if numbers fluctuate on the volt meter.