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Charge, no Charge

T

tjs88xj

NAXJA Forum User
Location
Auburn,Washington
About 3 weeks ago, I replaced my Serpentine belt, and on my next drive, my check gauge light came on, and my voltmeter was not registering. Shut the car off, came back on. Pulled the alternator out, took it down to the rebuilder. Told him to fix only what needed to be, since I am broke. He said everything was fine, but the brushes, and he replaced the brushes. I put it in, and it was charging around 13 volts running. After about a day, it was pushing 14, and all was good. Last night my check gauge light was on, and I wasnt registering again. Should I drop the money on a new alternator? He tested the components of mine and said it was good. The thing that gets me, is when I was still driving, I turned the key off and back on, and it was charging again. Any idea's? This is on a 99 classic, btw
 
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Year/engine would really help.

Some years alternator internally regulated, some years externally regulated with regulator separate on fenderwell, some years externally regulated with regulation provided by PCM.

Your problem could be as simple as corroded cable/connection, or a failing PCM.
 
Even if your alternator is fryed, the voltmeter should show the battery voltage. It sounds like a gage issue, or the wiring to the gage. Your voltage regualator is built in to the ECU, so hope that is not the problem. You need to test voltage at the battery with a multimeter. With the key off, it should read about 12.5 Volts. After you start it up, voltage should go up to 13.5 or 14. This shows that your alternator is working. As usual, dismantle all your battery connections and grounds in the engine bay. Clean them with scotchbrite or sandpaper, then clean with contact cleaner, brake cleaner, etc., and reassemble.
 
99 with the 4.0 and auto. I'll give all the suggestions a shot.Had an issue with the gauge cluster and the air bag light a few months ago. Hopefully it is something simple. Time to go clean some grounds. Thanks guys.
 
It could be even simpler. Is the serpentine belt tight enough? Does it come back if you wiggle the key? Could be the key is not spring back all the way to the run position (btdt).
 
Cleaned grounds, tightened belt, no go. Tried wiggling key, no go. I checked key off voltage, got 12.5. Key on running, got about 13.4, until I turned on the accessories(lights, a/c) and dropped to 12.8 slowly down to 12.4 when I stopped. On the way home, I ran around 13.25-12.75, at 70. I am thinking voltage regulator..(PCM)...
The gauge pegged down to 9 and check gauge light came on.. shut key off and back on, back to 13ish.
 
On your 99, it gets all it field windings signals from the PCM. So, what I,m saying is the computer tells when and how much for the alternator to charge. You need to check those inputs also.
 
Since your seeing it trying to charge with the voltage at 13.4, then, I would say the voltage regulator is probably working. Usually when it fails it stays dead. Bad or worn out brushes in the alternator would be more intermittent and heat dependent.
 
Measure across the two small terminals on the alternator for the field coil. One side should have +12 volts and the computer controls the ground side of the field coil. If you've got full voltage there and it's not charging, the alternator is bad.
 
tjs88xj said:
Cleaned grounds, tightened belt, no go. Tried wiggling key, no go. I checked key off voltage, got 12.5. Key on running, got about 13.4, until I turned on the accessories(lights, a/c) and dropped to 12.8 slowly down to 12.4 when I stopped. On the way home, I ran around 13.25-12.75, at 70. I am thinking voltage regulator..(PCM)...
The gauge pegged down to 9 and check gauge light came on.. shut key off and back on, back to 13ish.
Click to expand...

run it again and check voltage at the battery (still running) when the gauge reads 9V. It sounds more like a faulty gauge circuit or another circuit controled by the ignition switch than a faulty alt.
 
Shorty said:
run it again and check voltage at the battery (still running) when the gauge reads 9V. It sounds more like a faulty gauge circuit or another circuit controled by the ignition switch than a faulty alt.
Click to expand...

I'll see what I can do. The only time that happens is when I have been driving around town for a little while. I'll try carrying my DVOM with me and pulling over if I get the chance once it happens again.
 
Pulled the negative cable off, while it was running(later was told very bad idea) and it hesitated slightly, but kept running. Died as soon as I turned on fog lights. Tried again, this time with Max A/C died immediatly. Recently it has been running 13.5 ish until I turn on lights or ac, where it goes to the low 12's. I am still suspicious of the alternator, wondering if maybe a diode pack is going.
 
Both. The gauge in the dash is reading the same as the dvom. charges fine with nothing on. as soon as I turn on any accessories, the voltage drops, verified by both the dash gauge and the multi meter.
 
tjs88xj said:
Pulled the negative cable off, while it was running(later was told very bad idea) and it hesitated slightly, but kept running. Died as soon as I turned on fog lights. Tried again, this time with Max A/C died immediatly. Recently it has been running 13.5 ish until I turn on lights or ac, where it goes to the low 12's. I am still suspicious of the alternator, wondering if maybe a diode pack is going.
Click to expand...


Yeah, don't do that. You can fry the engine computer doing that. I assume you watched and verified the belt wasn't slipping. Otherwise, the alternator is suspect. Go have it load tested.
 
Your 99's voltage is regulated at the PCM. Your problem is either the Altenator or wire/cables attached!! I had this very problem on my 00 and it was a bad Alt!!
 
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Had the alternator Full field tested. Tested good again. Had him take it apart and check it over again. All good. Hasnt stopped charging in a while, however isnt charging as much as I would like at idle. Drops to 12.25-12.5 with lights and A/C on. Gonna do a bit more probing tomorrow with DVOM. At Speed, with Max AC and lights and radio on, seems to sit 13.5-13.75, which I could live with. Just like to see it actually charge at idle.
 
Just my two cents...it seems that it charges just find when driving and when the light/accessories are OFF at idle.

Correct me if I'm wrong, but the problem seem to be only at idle when any of the lights/accessories are turned on.

So, it seems that it is NOT charging with a load at idle, correct?

Dumb question here...but what is your idle like with no light/accessories...what is it like when you do turn on the lights/accessories?

The PCM, when it senses a high electrical load should bump up the idle so that the alternator can compensate...for example, when you electric aux cooling fan kicks in, the rpm should go up a little.

It still might be the PCM...if it doesn't sense the electrical load and compensates for it, it still could be bad. Any chance you could try another PCM?

Oh, one thing you can do...at idle...give it a little gas...run it to about 800-1000 rpm...and then turn on the lights/accessories and see what happens.

Another things...if you belt is not tight enough...it could be slipping which would not turn the alternator fast enough to make enough volts. It can slip and make no noticeable noise.

good luck
 
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