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Troubleshooting Diagnosing problems done here.

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  #1  
Old May 22nd, 06, 07:12 AM
STM69 STM69 is offline
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Default Good alternator not charging... whats wrong?

This is the problem. I swapped out new heads and cam. I unplugged and removed the alternator. When everything was re-installed I ran the car for a while and the battery died. It was an old battery. I bought a new one and the darn thing died too. I think that was because I had the wires reversed going to the alternator. With some help I figured out the correct wire and ran them correctly. I installed a new voltage regulator (because it was inexpensive) and I had the alternator tested at two different shops. Both said it was good. But now I can see that while the car is running the lights are dimmer than they were 2 hrs ago, the radio is on but there is no power to it unless I rev up the RPMS...the battery is going dead again.

Here is some other info that may or may not help:
The alternator test good twice but each time there was "N/A" for the diode test. The wire going from the voltage reg. to the alternator is good. (read 0 when doing resistance test).This is externally regulated. Is there a diode in the alternator? A new one off of the shelf also tested "N/A" for the diode test.

I'M STUCK! HELLLP!

Last edited by STM69; May 22nd, 06 at 07:23 AM.
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  #2  
Old May 22nd, 06, 07:18 AM
JimM JimM is offline
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Default Re: Good alternator not charging... whats wrong?

You need to pick up a cheap digital volt meter (see the electrical basic article in the sticky at the top of electrical for what to buy and how to use it) and then read and do the voltage tests in the article on external regulated alternators in the same sticky.
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Old May 22nd, 06, 08:00 AM
STM69 STM69 is offline
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Default Re: Good alternator not charging... whats wrong?

I'll check on those numbers. By the way, what is the little round thing that plugs into the regulator that looks like an old M80 firecracker? I know that whatever it is...its original and probably needs replaced.
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Old May 22nd, 06, 08:06 AM
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Default Re: Good alternator not charging... whats wrong?

thats a condensor to limit noise to the radio from the elec. system.
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  #5  
Old May 22nd, 06, 10:29 AM
camro tyler camro tyler is offline

 
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Default Re: Good alternator not charging... whats wrong?

i had the exact same problem on my 68 ss 350. the blue wire and the white wire coming from the alternator had to be switched on the regulator i had them in the wrong position. now my only problem is the car will not shut off but i believe that could be i need a diode at the brown wire back to my ignition. but my alternator is now charging the battery
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Old May 22nd, 06, 11:23 AM
STM69 STM69 is offline
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Default Re: Good alternator not charging... whats wrong?

I have the blue wire coming from (F) on the reg. to the (F) on the alternator....still not charging...but I'll chekc on the voltage numbers tonight.
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Old May 24th, 06, 04:33 AM
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Default Re: Good alternator not charging... whats wrong?

It is very easy to short out an altenator when working on you engine.
One of my SS heater hoses touched my altenator and from that time on it would not charge.
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Old May 24th, 06, 06:49 AM
clill clill is online now
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Default Re: Good alternator not charging... whats wrong?

If it is charging the bearing cap in the center of the rear of the alt will be magnetized when it is running. Hold a screwdriver up to it and check.
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Old May 24th, 06, 08:50 AM
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Default Re: Good alternator not charging... whats wrong?

Quote:
Originally Posted by clill
If it is charging the bearing cap in the center of the rear of the alt will be magnetized when it is running. Hold a screwdriver up to it and check.
The more current being generated, the stronger the magnetism, the stronger the "pull" on the screwdriver.
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Old May 24th, 06, 09:34 AM
STM69 STM69 is offline
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Default Re: Good alternator not charging... whats wrong?

SCHOON,

Hmmm.. Yes I did accidentally touch the alternator twice with a wrench and got a big spark. That would definately explain it. BUT, why would the alternator test as "good" at both AutoZone and Advance Auto?
I'll test for the magnetism tonight
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Old May 24th, 06, 09:59 AM
JimM JimM is offline
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Default Re: Good alternator not charging... whats wrong?

alternators test good but don't work if one or more of the diodes inside are bad.
There are 6 separate diodes, fed from 6 separate coils, 3 go to ground, 3 to +12 volts. Total output is added together from each.

Any open diode would reduce output by 1/3.
Since the alternator is still producing some power, it passes the test. It will also pass the magnetism test unless you have a very well calibrated hand.

I'm pretty sure the testers will only show a shorted diode, not an open one.
I've had bad alternators test good to.
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Old May 24th, 06, 11:15 AM
SCHOON SCHOON is offline
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Default Re: Good alternator not charging... whats wrong?

Jim's right,
It turned out I blew a few diodes but the altenator was still looking good.
It also caused short in my bat that was hard to find.
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Old May 24th, 06, 11:59 AM
STM69 STM69 is offline
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Default Re: Good alternator not charging... whats wrong?

Oh man I hope its that easy... Also, when I got the alternator tested...the machine tested 3 things...(can't remember each), anyway, the diode test was one of them and it came back as "N/A". I thought that this was odd, so I had them test a reman. one that they had for sale. It tested "N/A" for the diode too. These are externally regulated...Does a externally reg. alternator have a internal diode? Or do I have a external diode somewhere?? Is my battery going to need checked since shorted the alt?

Jim,
If one of my diodes are bad then I shouldn't be getting 12v back to the battery... which wire would I check for alternator output? I did read the sticky but it'd be easier if you'd point out the exact wire I should be looking testing... Thanks for all the help...
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Old May 24th, 06, 12:24 PM
fdny37 fdny37 is offline
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Default Re: Good alternator not charging... whats wrong?

I had an alternator tested at three different auto parts houses and they all said it was good. I then purchased an alternator on ebay that was correct for my particular car and then had it restored. Wouldn't you know as so as I bolted it up the system was working perfectly. I also had them bump up the amps and now I have a great looking and working alternator and charging system. Moral of the story, go the extra step and deal with people that know what they are doing. I know that it will take more time having original parts rebuilt as opposed to just going to the parts store and bolting it up the same day, put you get what you pay for. In the long run it's probably a push money wise. I know this doesn't help your problem right now but I think if you start with parts that you are certain about and check your wiring I'd bet that it will work fine.
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  #15  
Old May 25th, 06, 04:18 AM
SCHOON SCHOON is offline
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Default Re: Good alternator not charging... whats wrong?

FYI,
Some of the chrome plated altenators the big Speed Shops like Summit sell have a GM stamp on them. They are really made in Tiwan or some far away cheap labor place. The diodes they put in them along with the other components are pure crap.
We rebuilt ours with parts from an older real deal GM altenator.
Worked fine since.
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