99 suburban from hell!

[tks89blazer]

Hey i was just posting to pick some of your brains a little bit and see if anyone has any ideas for this suburban. i am a mechanic at a local shop in MI and i have a suburban that is burning through alternators. i have voltage drop tested all the power and grounds with no luck. the battery is new and it still fries the alternator after about 30 sec its burning hot. the alternator is a 140 amp from factory and it is all internally regulated with a single exciter wire which is all working. i have put on 4 alternators just to try and test it and they just burn up to fast. if you have any ideas or more questions please let me know thanks for looking.
TK

 

[dbreid]

Sounds like the battery has a bad cell and is causing "alternator death?" Can you verify the battery takes a charge from a trickle charger?

 

[Fordum]

First, before you do anything else, run a heavy wire from the battery negative terminal directly to the case of the alternator. A flaky ground to the alt. will burn one up fast.

Otherwise, not totally sure whats doing it, but it should be easy to find. First, mount the alternator, and then with the engine off, touch the output wire to the stud. If you get a spark, somehow the polarity is reversed. Don't really think that's it, but if they burn up that fast.......
Now, you are going to need a dc voltmeter and a DC clamp-on ammeter. The voltmeter is fairly easy, but the ammeter might be a problem. A regular clamp-on ammeter won't work, it has to be a DC version. They are a lot more common then they used to be, so you should be able to find one.
If you didn't get a spark when you hooked it up, then hook the dc voltmeter up to the output stud,, and clamp the ammeter around the output wire. Measure the voltage at the output stud with the engine running, and the current. Its probably going to be less than 14.5 volts, and pretty high amps.
If so, then quickly measure the current in the positive cable hooked to the battery.
If its high there, then you have a shorted battery. If its high at the alt and not at the battery, then you have a short somewhere else.
And it is something that is occurring only when the engine is running, or else the battery would stay dead.
Let us know what you find.

J.

 

[tks89blazer]

I have put the battery on a trickle charger and it seems to hold a charge just fine. I am off work for the weekend but when i get back i will give the ground wire idea a try. i have not been able to use a amp clamp due to the fact that mt boss has not purchased one for the shop and i dont have the extra $$ lying around right now. i will have one on thursday because my boss finally realized that its practically impossible to diagnos this stuff without one. thanks for all the ideas it really helps the thought process out with other peoples ideas. i will post an update when we get it diagnosed. Thanks a ton TK

 

[tks89blazer]

found the source of the alernator burn ups. found out that the belt was not being held tight by the tensioner and it was causing the belt to slip on the pulley and heat it up melting the internals of the alternator. thanks for all you info and help. TK