It says in the manual that the correct Voltage output on a running engine should be 14 to 15 Volts from the alternator. Right now the Alternator is only giving out 13.7 Volts. Is the alternator on it's last legs or is it perfectly fine?
Its strange I went to Kragen to get the free diagnotic on the alternator/battery and they said the Diods were going bad and the voltage was low. Then I take the car to Autozone to get a second opinion the same day and their scanner says the diods are fine. The voltage a bit low but at the same time A-OK. So who is correct? When is it time to get a new alternator? At what voltage output should a new Alternator be warranted?
Normally we would bring the engine up off idle to measure voltage (I also like to measure at about 2500 rpm or so to check for brush float). If the battery state of charge is low or electrical system demands are high, alternator voltage an be reduced by the load - especially at idle.
Charging system loads can sometimes affect alternator ripple readings... again, my own preference is to use a DMM set on AC volts to measure from the alternator to a good engine ground in order to reduce the "smoothing" effect of the battery.
A "good" AVR test would also include measuring alternator current output with an inductive type ammeter.... a carbon pile may be required to load the system enough for this measurement. Anything over about 85% of the alternators rated output would be considered adequate...
First off you must know it is more likely than not that the kids working at Autozone and Kragen DO NOT know how to check it correctly. Second, are you having a problem? There is nothing wrong with 13.7, especially at idle with accessories on... I could write a book about the stupid things the parts people at Kragen and Autozone have told me.
The spec is supposed to be 13.8 Volts at (IIRC) 68 degrees Fahrenheit. And there is a thermistor in the regulator to match the proper float voltage to what a lead-acid battery needs to see, which can go up over 15 volts on a really hot day.
13.7 is in the "gee, my meter isn't calibrated quite right" range. You need a metrology laboratory for that one... ;-P
Have you ever seen the butcher put his thumb on the scale?
The person running the alternator test stand can have ulterior motives and make the test come out either good or bad if they want it to - and unless you have some experience at it, you'd never know...
I'm going to put on my Karnac the Magnificent Turban here:
The salesman at Kragen wanted to sell you a rebuilt alternator. (Cha-Ching!) They have daily sales targets to meet, and he wasn't there yet. Autozone probably sold you this rebuild a few weeks or months ago. He doesn't want to eat a warranty exchange unless the machine can prove beyond a doubt it's stone cold dead, so the vendor won't argue about the back-charge. Sound about right?
The bottom line is, does it put out enough voltage, enough of the time, to keep the battery fully charged? If not, get another alternator. One of those LED lighter-socket voltage monitors will tell you without staring at a DVM while driving - the voltage will drop at idle, but it should go up into the green and stay up while the vehicle is moving.
All the chain parts stores get their alternators from rather sloppy "factory rebuilders" who only clean them up and replace totally bad parts like worn brushes and noisy bearings, but they are not very thorough. If they get that alternator to the point where it 'passes' a run on the test machine they call it "Done!", stuff it in a nice shiny box and ship it. And if there are any other problems you'll find them and send it back.
My record was swapping alternators four times in the parking lot of a Kragen till I hit one that actually worked. (Too far away from my usual shop to chance getting there while running on the battery.)
Go find a local or regional rebuilding shop where they actually do the work and know what they are doing. I drive across town to Mission Auto Electric in Pacoima CA, and go wander off for a few hours while they do their magic - but when they hand me back the part it will work, period.
(Ex.: On the newer Delphi units, they know to toss the factory regulator and diode matrix at the first hint of failure. They're both piles of crud made to a low price target, because they only need to last past the warranty. And you wonder why Delphi went Bankrupt...)
Ask the local independent mechanics in your area where they go - they want rebuilds that work the first time, because they have to eat the labor for the repeated swaps whenever they get a bum one. Chances are it isn't a chain 'beauty parts' store.
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