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Voltage Dropped & Then It Died

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89Blazer4wd

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Woodbridge, Va.
Over the last two days the voltage gauge has been real low while driving. Its usually straight up and down at the 13. I noticed yesterday that the needle was half way between the 8 and the 13 while driving. But no problems with the truck starting or anything like that. By the time i get to work this morning the needle is sitting on the 8. At lunch time i go to leave, it starts, but its weak. I left it running while i was in the bank because i feared it wouldnt' start back up if i shut it off. So then i just drove straight home to drop it off and get my other car. The truck died as i was pulling into my spot. Battery still had juice when you turn the key to on, but it wouldn't start or even turn over.
So what do i look at first and what do i test? I looked in the service manual and it says to check the volts at the battery before starting (should be 12 if it wasn't just about dead now) and then check it once it's running and it should be about 13-15 then. The book also said something about sticking a screw driver into the back of the alternator to short it out and check the voltage then. (and not to do that for an extended period of time because it is unregulated volts and could cause harm). Ok so what am i looking for? If the volts at the battery when its running is below 12 then its not charing and the altenator is defective? What if the volts are good there and not good when I do the screwdriver test? what is the faulty part then?
Any suggestions on where and how to look for the problem would be a huge help. The generic service manual is terrible.

Thanks,
Patrick
 
Sounds like your alternator is going out. If possible, start the Eng. and use a digital volt meeter on the lug at the alt and it should read around 14 volts -/+ if not, then it's not charging and it's time to replace the alternator.

Dan..
 
The screwdriver is to bypass the internal volt regulator. This way you can check the output of the alternator. If the voltage is correct, using the screwdriver, then I would replace the regulator. Course, you gotta remove the alternator to do this, so unless money is an issue, just get a new alternator.
 
Just be glad it didn't die and leave you stranded on the side of the highway,,,:crazy:
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:doah: Front bearing is toast, as well as the internal components,,,,literally
 
check this first...

After you charge the battery up,start the truck and use a test light to see if power is at the 2 wires that plug into the altenator..(73-87 trucks--newer ones I am not very familiar with)..BOTH wires should have 12V with the motor running..if the white or brown wire has no voltage,the altenator feild will not get its needed excitation,and it will not charge!..

Also check the thick red wire that goes to the stud on the altenator,make sure it has 12V,and is not damaged or melted anywhere...same for the fusible links at the starter soleniod,and near the brake booster..either of them fail,it can prevent charge from getting back into the battery..(you'd have other troubles too,so they may not be at fault)..but check them anyway...

You probably cant get a screwdriver in there to test the regulator, with it installed--you'll have to pull it,best thing is to have a place like Auto-Zone test it on the bench..if it IS junk,at least you'll have the "core" and wont have to pay the core charge..

I have about 6 GM alternators in my garage for spares,that my friends were going to junk because they thought they were junk--but all of them worked fine,I found other problems on their trucks(mostly that brown or white wire being "dead" due to corrosion!),after the battery went dead again with the rebuilt alternator they installed!...dont be too quick to condem the alternator!..)unless its toasted like the one pictured in the last post!--then I guess it IS junk!)...:crazy:
 
You can rebuild a GM alternator for about $20, no idea how much they cost already rebuilt, but it's so easy I wouldn't pay more than $30 rebuilt. Especially since the parts store rebuilds are going to use no better parts than what you can buy as a rebuild kit.
 
yup...easy to rebuild after you do a few..

I usually do just that--buy a "HELP" brand rebuild kit and put in the new regulator,diode trio,and regulator..last one I bought was 13.99 at Pep Boys..--its a bit tricky,but easy once you've done a few..

...if it needs bearings,I pass...I've tried doing the bearings,its tricky,time consuming, and you really need a press to do it right..the cases often corrode so badly you cant get the bearings out without cracking them quite often..thats when I head to the boneyard for a good used one for 20-50 bucks,depending on the year and amperage..

I've bought many alternators "cores" customers brought in to the parts store,to get the core charge deposit..and rebuilt them myself..cheap way to get a hi-amp alternator!:D ..(and more than one had NOTHING wrong with it,because the car had other ailments,like fusible links or bad battery cables,etc,)...:bow:

I've had better luck with original ones off wrecks ,than the rebuilts at some discount parts houses..I avoid the "rebuilt" ones with stickers on them if I see them in a junk car..usually means the car had electrical problems they couldn't diagnose..most of those I bought and tested had one or two diodes in the trio blown,but still charged enough to keep the "ALT" light off...or other dilemas..

I haven't gotten around to it,but I still would like to take one or more of the "spare" alternators and try making a welder ,like the ones I see plans for on the web,using a small gas engine..I have all the parts,just no time to mess with them now..someday soon I will,cause I need a welder,my arc welder is dead ...:crazy:
 
So if i wanted to experiment with rebuilding the alternator opposed to just trading it in and buying a reman or new one; where would i go to find a rebuild kit for this thing? And judging from the fact that my alternator looks nothing like the one thats shown in the service manual, how do i know that i'm getting the right kit to rebuild mine?
Otherwise its $95 plus $30 core charge for a reman locally. I'd prefer not to pay that kind of money for one that isn't even knew.
 
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PLEASE !!!, DO NOT BUY A REMAN'D UNIT !!:doah: :p:

:D The one i posted up a few before this, WAS a REMAN'd unit, i was alittle short on cash when the original died, and then again a year and a month later when the second REMAN'd unit died, this was the second REMAN'd unit that fried, see a pattern here???

I have decided to just get the cash together, and buy brand new, lifetime warranty stuff,,twice now, these REMAN'd things have died shortly after the warranty was up, and this second one, almost took out the whole truck.
 
You'll have to track that down. I don't have any links handy, but I know it's been posted before, a site that shows the various alternators and what they are called.
 
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