QuestionQUESTION: hey man
i asked a question two weeks ago about the alternator on my accent and i have followed your suggestions...here's the deal: i have replaced two batteries, an alternator, taken the alternator back to the parts store, had them check it, it tested fine...checked the battery wires from the + to the alternator, taped up potential problem areas, checked the alt. fuse...looks fine...but still i have this issue: when i use a voltmeter to check the battery voltage, it reads 12.6. when i turn the car on, the alternator stays at a steady 14.1 for a minute or two, then the voltage starts to drop gradually...then the car starts to idle rough...any new ideas..this car is about to worry me to death!!
thanks
ANSWER: Gotcha. The part that concerns me is that the alternator begins to drop off the 14.1 after a couple minutes. 12.6 prior to starting the car is not bad, but this is also a no-load voltage, so it doesn't necessarily reflect the battery's state of charge, either. Hopefully, your answers to the following will get me to the bottom of what's occurring:
1. How low does the voltage drop after it begins dropping off the 14.1?
2. What is the approximate voltage when the car begins to idle rough?
3. Is your engine running at the proper RPM when the voltage begins to drop (below 13.5, if it gets that low)?
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QUESTION: 1. the voltage usually drops to around 13.2
2. the voltage when the car idles rough fluctuates with the surge of the idle...sometimes it will fluctuate from 13.2 ish to 15
3. the surge in voltage and idle happens from around 750 surging to 950. all the while causing the instrument panel lights and headlights to dim and brighten consistent with the rpm pulse.
ANSWER: Okay. 13.2 is enough voltage for the ECM to operate the engine properly. I'm suspecting that the low rpm is causing the voltage to decrease. If I recall correctly, this car has one of the metal can-looking idle actuators. If so, whack it with a wrench while your rpm fluctuation is occurring. If that makes the fluctuation stop, you should replace the idle actuator.
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QUESTION: last one, i promise, you've been very helpful, thanks alot.
so when i whacked it with a wrench, the car stopped fluctuating, but the alternator also stopped sending a charge to the battery. now, when i measure the voltage at the battery with the engine not running, it measures 12.6, but when you measure the voltage with the engine running, it drops to 12.3 or less...so, i know i need to replace the $200 idle actuator, but will that solve the charging problem?
thanks
AnswerIf your idle speed is normal and you have 12.3V with the engine running, there's a charging system problem.
Verify you have the same voltage at the lug on the alternator. This would indicate that the problem is in the alternator and not somewhere in the circuit between the alternator and the positive battery terminal.
Unplug the alternator and turn the ignition on without starting the engine. Check the voltage in each terminal of the connector. On should have roughly battery voltage, and the other (which goes through the warning lamp) should have about 7V or so if I remember correctly. Also check the voltage between the alternator case and the negative battery terminal. It should be less than 0.5V. The purpose of all this is to check that everything is getting to the alternator as it should and that the circuit between the alternator lug and the battery terminal is okay. If the results of these tests are all as I specify, you have a bad alternator.
And don't worry about the follow-ups. It's difficult and lengthy to try to address each possible scenario right from the outset. If my answers so far don't provide you with what you need, continue to follow-up as necessary.
