Is my Alternator dieing?

[AaronFL]

I have a 2001 RT/10 with 21K miles. I've owned it since February and have put 2K miles on it. I have had a bunch of little issued with it and I am thinking they are all relating back to a failing alternator. I figured I would post on here to see what you all think.

Volt gauge is always 12-12.5v when driving around (never 14v like I have read on here)
Horn sounds anorexic
Windows move down slow as hell
Radiator fan functions intermittently (almost overheated a couple of times)
It has to charge on the battery tender for several hours after each drive to reach full battery charge

Does all this sound like the alternator is weak? I had a new Interstate battery put in back in March. The car was stored for 3 years before I bought it and it was a track car for most of its like.

Thanks for the help!

 

[daveg]

Put a Volt meter on the jump points under the hood on left to double check actual voltage when car is running. If still low, take alternator out to have it tested. Also check belt tension.

 

[AaronFL]

Thanks DaveG...will do and report back.

 

[gb66gth]

You can alos test the alternator by running the car and taking off one battery lead. If the car dies within a short period of time, it's your alternator.

 

[speedracervr4]

^^^DON'T do that on newer vehicles, you can fry the PCM. It has been discussed before. The service manual has good tests to determine what's wrong with your charging system. Follow them.

 

[AaronFL]

Update:

I took a volt meter to the post under the hood by the PDC. The car has been sitting on the battery tender since this morning. With the car off and battery tender disconnected, I get 13.7v. With the car started and idling 12.6v. With the headlights on 12.0v. I turned the lights back off and it went to 12.3v...but the idle may have been a bit lower at this point due to the car warming up. I checked the pulley on the alternator and it is spinning.

Before I get a new alternator, could this be the battery temperature sensor?

I am going to dig out my service manual and see the protocol for testing these two.

Thanks again.

 

[AaronFL]

Update 2:

Now that the LeMans excitement is over, I went out and re-probed.

Voltage at the alternator is 12.9v during idle...grounded with the ground bolt below 6 inches away
Voltage at post on driver side 12.6v.

I don't have any safety wire on hand to increase the length of my probes to direct measure the voltage between the +alternator and +post... but I am assuming this means a voltage drop of .3v between the alternator and battery. I am a newbie to all this obviously. Does it matter that I used the ground by the alternator and not the ground by the jumper post to get the alternator voltage? I am assuming no.

Is 12.9v an acceptable output at idle?

 

[speedracervr4]

That is low, most will be in the 13.9 range. Did you turn the lights and a/c on while doing the test to see if it dropped or raised? Either way 12.9v is too low.

 

[AaronFL]

Thanks for the replies. I am going to get a new alternator and put it in. I will update back here when it is installed to complete the thread.

 

[spikeone]

figure I will ask in this thread instead of opening another one

my voltmeter is usually around the 14V mark but sometimes it will go up a bit more and then the battery "icon" will light up, it will then go away after a little while, seems to happen more often after a hard acceleration

have no trouble starting the car and battery is new from last year

is this just another "viper mystery" or could my alternator be on its last breath?

 

[daveg]

Could be the Voltage regulator if it's putting out TOO much voltage.. at times..

 

[spikeone]

Could be the Voltage regulator if it's putting out TOO much voltage.. at times..

can't check service manual since I am at work but is there a way to check this and how hard is it to change ?

 

[SquadXX]

^^^DON'T do that on newer vehicles, you can fry the PCM. It has been discussed before. The service manual has good tests to determine what's wrong with your charging system. Follow them.

Also if ur running an aem like me, You can also fry it by jump starting ur car.
Happened to me twice before i figured that out

 

[AaronFL]

Update:

I swapped out the alternator finally. It wasn't too hard at all. I tested the voltage coming out of the alternator at idle, at it was 13.4v (up .5v from old alternator) with the newer alternator. Unfortunately, it didn't fix my problem. If I turn my lights on, my battery voltage drops down to 12v. Hmmm

 

[AaronFL]

Another Update:

I installed another new OEM Denso alternator and got the same result. I took it to my local Viper Tech and they hooked up the DRB to it and said that it was "within the range it was supposed to be". However, 12.5v with the lights on cannot be correct from my understanding.

I checked the tightness of the harmonic balancer, installed a new battery temperature sensor, swapped out the ASD relay and fuse, and still no luck...still on the low side for volts.

I remember Tom Sessions telling me before I purchased the car that the PCM was reflashed by DC performance if I remember correctly. I wonder if it is the PCM that is messed up or something else? Any ideas?

 

[Dan Cragin]

Odds are you have a voltage drop issue or that new battery is defective. Have the alternator tested with a load tester to see actual output. Do you have a smaller crank pulley? Many race spec cars change this and it will not charge enough at low speeds. If it is a computer issue, it would not charge at all. The reflash would not cause this.