Alternator Putting Out 9v

[95strokerPSU]

Like the title says, my alternators not putting out enough voltage. At first start up it's at like 11.30v and then after a couple minutes its down to around 9v. When I rev it up, the voltage doesn't increase. It's still got a stock sized pulley on it.

I took it to Autozone to have it bench tested and the brain child there said he couldn't do it because the prongs on my voltage regulator were too wide. I find it funny that about a month ago I took the same alternator there and had another guy test it without a problem using the same machine.

Anyway, I won't be able to get to another store till maybe Sunday, so I just wanted to post this and see if the problem I'm experiencing is a tell tale sign of something wrong either with the alt or maybe with the voltage regulator.

Thanks
Dave

 

[HISSIN50]

Dave, is there any differential between the battery voltage and the alternator voltage? Does the voltage continue to drop, or does it go back to 11+ volts after each stopping and restarting?

I've had some horrible experiences at the parts stores too (e.g. one time the guy ground the alt's external fan blade into the frame of their testing machine). I woulda found another store or dude to help (time allowing).

It sure sounds like the alt, but a bad battery can mimic a bad alternator.

Things to check real quick: check the fusible link for the alternator. It's next to the PS (between the pump and distribution block IIRC). Peel back the regulator wiring harness loom and check for bare wires. If you have two shorting, that can cause issues. I had bare wires on all of the reg wiring (the insulation vulcanized and came off).

And make sure the connection at the back of the alt for the charge cable is good, as well as the connection at the distribution block. The latter is known for corroding, which would keep the alt's charge from making it into the system. I say this because if the alt is ok, the lack of voltage could be an IR issue.

Good luck.

 

[95strokerPSU]

No difference at all between battery voltage and alt voltage. Everytime the voltage output would get down to near 9v, the car was almost stalling out at that point, so I would turn it off, recharge the battery and then if I fired it again, the voltage output is back up to 11.30.

Before I start tearing anything apart, I guess I need to get the alt bench tested.

 

[kornchild4life]

I think if you let the car run and you take the negative termal off the battary and its dies that normally means the alt. is shot? anyone back me up on this

 

[95strokerPSU]

I was thinking disconnecting the battery might determine a bad alt, but I wasn't 100% sure that's a legitmate test.

 

[1TallMF]

I was thinking disconnecting the battery might determine a bad alt, but I wasn't 100% sure that's a legitmate test.

Back in the olden days of carburated cars, that was an easy test to isolate an alternator problem. With computer-controlled cars, unhooking the negative battery cable while the car is running can potentially fry the ECU and other electronic components. I would advise not to try this. Sounds like the alternator is not puting out anything at all. Could be a faulty regulator or a bad connection at the distribution block or the alternator.

First thing you should likely do is get the alternator properly tested by someone who knows what the hell they are doing. The 2 guys that tested mine on the weekend (thats right, it took 2 half-wits to figure it out) took a good 20 minutes to find the correct plug for their machine
Heh, they told me I had the wrong alternator in my car, and that it should have been the 65-amp one with the external fan.... 'nuf said.

 

[HISSIN50]

Back in the olden days of carburated cars, that was an easy test to isolate an alternator problem. With computer-controlled cars, unhooking the negative battery cable while the car is running can potentially fry the ECU and other electronic components. I would advise not to try this. Sounds like the alternator is not puting out anything at all.

Quoted for reinforcement. Dont disco' the cable with the car running.

 

[mo_dingo]

With the alternator running, you could see 14V AC at the main cable.

Also make sure you are getting 12V DC going to the alternator, otherwise the magnetic field will be too weak and AC voltage output will be minimal.

If the alternator is putting out 14V at startup, then test the diode packs and see if they are converting it to 14V DC. If they are the culprit, you likely will find a nasty voltage drop.
Scott

 

[95strokerPSU]

Just got the alternator tested and everything is fine with it. The cable from the alt to the dist block is fine...I don't have a fuseable link it's just one piece that I cut myself to reach the new location of the dist block. If I don't have a thick enough gauge could that possible cause problems? Battery is in the trunk...2/o cable from dist block to battery.

Guess the next thing I'll check and make sure the positive lead going to volt reg. is getting 12v. What would the alt output be if the volt reg. was getting 0v? I'm just trying to rule out that when I cut the wires and extended them that I switched the ground and positive around.

Thanks guys

 

[95strokerPSU]

Also what would alt output be if the stator wire wasn't connected?