Alternator Test
Alternator Test Before the flaming begins for another alternator post, I promise I searched for this and read a TON of different alternator threads.
I'm having issues with voltage bouncing up and down from 12 to around 15/16 and my AutoMeter fuel and nitrous pressure gauges are not giving accurate readings (bouncing all over the place.....the N2O gauge shows pressure on the line even when the bottle isn't in the car and the N2O line is disconnected).
Based on my research, it seems this indicates there's an issue with the voltage regulator inside of the alternator. The question I couldn't find an answer to is if there's a way to test this (or if this in itself is enough information to just go replace the alternator). I gather most machines that test the alternator will test if they don't provide a sufficient charge and given these symptoms it seems it might not recognize the problem (mine is charging, however it's not properly regulated). Any advice on the next step?
I'm having issues with voltage bouncing up and down from 12 to around 15/16 and my AutoMeter fuel and nitrous pressure gauges are not giving accurate readings (bouncing all over the place.....the N2O gauge shows pressure on the line even when the bottle isn't in the car and the N2O line is disconnected).
Based on my research, it seems this indicates there's an issue with the voltage regulator inside of the alternator. The question I couldn't find an answer to is if there's a way to test this (or if this in itself is enough information to just go replace the alternator). I gather most machines that test the alternator will test if they don't provide a sufficient charge and given these symptoms it seems it might not recognize the problem (mine is charging, however it's not properly regulated). Any advice on the next step?
Joined: Nov 2003
Posts: 11,321
Likes: 341
From: Jacksonville, FL (originally from Toronto Canada)
If the alternator output voltage is varying enough to cause problems with your gauges then it will be readily apparent by just using a standard voltmeter across the battery terminals while the engine is running. You would also have numerous other symptoms such as dimming lights.
If the alternator output voltage is varying enough to cause problems with your gauges then it will be readily apparent by just using a standard voltmeter across the battery terminals while the engine is running. You would also have numerous other symptoms such as dimming lights.
Definitely having the dimming light issues. With the car idling at a normal level, I'm still getting 14-15 volt readings with the lights, stock radio, heater and rear defrost on and the car has a 25% underdrive pulley. Just seems odd to me that it would read this high when before this issue it would read in the 12-13 range with all of the accessories on.
Is that in itself enough to signal that it's time to replace the alternator?
Joined: Nov 2003
Posts: 11,321
Likes: 341
From: Jacksonville, FL (originally from Toronto Canada)
Normally I would say no, don't replace an alternator (or any other expensive part) based on symptoms and not on specific testing. However, your car is 11 years old and probably has the original alternator so it wouldn't hurt to replace it - it's going to need replacing eventually anyway (GM alternators are notorious for that) - if it's within your budget.
Still, diagnostic testing is always the best way to prevent randomly changing parts searching for a solution. If you have a voltmeter (or multimeter), it will only take a few minutes to test if the voltage is varying significantly.
Still, diagnostic testing is always the best way to prevent randomly changing parts searching for a solution. If you have a voltmeter (or multimeter), it will only take a few minutes to test if the voltage is varying significantly.
^ This is why I still have (and really like) my analog voltmeter. Perfect for this kind of thing. Sometimes, fluctuations are hard to see on my cheap digital meters because they sample so slow.
Thanks for the guidance.
I'll get my voltmeter and give the test you noted above to look for fluctuations in voltage at the battery. Forgive my ignorance, however I'm guessing it's as simple as positive-to-positive and negative-to-negative between the battery terminals and the voltmeter while the engine is running....and if the readings are floating up and down between 12-15 volts wildly, it confirms there's an issue with the regulator within the alternator.
I'll get my voltmeter and give the test you noted above to look for fluctuations in voltage at the battery. Forgive my ignorance, however I'm guessing it's as simple as positive-to-positive and negative-to-negative between the battery terminals and the voltmeter while the engine is running....and if the readings are floating up and down between 12-15 volts wildly, it confirms there's an issue with the regulator within the alternator.
It seems to me that a forum member should not to beg forgivness about asking a question before he asks. I've not been here in a while but........... is this what it's come down to.
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I agree - except for "what kind of oil" threads or "My gauge tells me I have bad gas mileage" threads. Those do require a preemptive apology.
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Verdad Gallardo it's as simple as positive-to-positive and negative-to-negative between the battery terminals and the voltmeter while the engine is running....and if the readings are floating up and down between 12-15 volts wildly, it confirms there's an issue with the regulator within the alternator.
IMO - watching the gauge fluctuate wildly is pretty reliable and accomplishes the same thing as above. It's essentially just a small voltmeter in itself.
Correct. Except you'll need an analog meter (with a needle) or a fast sampling digital meter. (Some digital meters may not show you the fluctuations very clearly.)
IMO - watching the gauge fluctuate wildly is pretty reliable and accomplishes the same thing as above. It's essentially just a small voltmeter in itself.
IMO - watching the gauge fluctuate wildly is pretty reliable and accomplishes the same thing as above. It's essentially just a small voltmeter in itself.
EDIT: Looks like the "DCV 50" setting on this one should do the trick. I'll check this out tonight after work.
Last edited by Midnight02; Jan 9, 2014 at 08:37 AM.
Tested both the battery and alternator today....I had both a voltmeter and a scan tool (both of which provided very similar readings) Results weren't exactly what I was expecting:
Battery voltage: cold, car off was between 12.05 - 12.20 volts
The reading on the voltmeter when connecting to the battery with the car idling, lights, AC, defrost, radio, (all accessories on) ranged from 15.10 - 15.50 volts. It would occasionally bounce a bit but not wildly like I expected it would.
Doesn't 15.10+ volts at idle with all of the accessories drawing power seem really high? Car also has a 25% UDP. If I'm interpreting this data correctly, the alternator is charging however it seems the voltage regulator is not working to keep it within the ideal range.
Battery voltage: cold, car off was between 12.05 - 12.20 volts
The reading on the voltmeter when connecting to the battery with the car idling, lights, AC, defrost, radio, (all accessories on) ranged from 15.10 - 15.50 volts. It would occasionally bounce a bit but not wildly like I expected it would.
Doesn't 15.10+ volts at idle with all of the accessories drawing power seem really high? Car also has a 25% UDP. If I'm interpreting this data correctly, the alternator is charging however it seems the voltage regulator is not working to keep it within the ideal range.
Joined: Nov 2003
Posts: 11,321
Likes: 341
From: Jacksonville, FL (originally from Toronto Canada)
Over 15 volts is too high and will eventually boil your battery. The ideal output voltage to the battery is in the range of 14.2 to 14.6 volts.
Yes sir. Have an alternator on the way and will get it swapped out this weekend. Thanks again for all of your help with this.
UPDATE: Had a little setback. Got a KG3 alternator from a 2003 Yukon. Pulled it out of the box and the plastic 4 pin connector is cracked so the male end of the plug will not attach securely. Does anyone know if this part is replaceable and/or interchangeable with the stock f-body alternator?
from what I can see, that plastic is part of the voltage regulator and has to be replaced as a whole piece, but that is probably the part that is faulty on your old alternator, you can find them on ebay new for under 30.
Just an update -- picked up one of the AD244 alternators from a 2004 Express Van on ebay for $35 and installed it earlier this week. I coordinated the install with a front sway bar swap so it was great having the extra room to work on the alternator.
Here are a few of my notes from the install:
1. The "truck" alternator lined up well with the mounting bracket and bolted in without issue.
2. Since the plug for the exciter wire is rotated a bit from the stock 105 amp alternator, I only have about a half inch of "play" left in that wire.....if it were rotated any further down it would require extending the line.
3. I have a 25% underdrive pulley and was running a 75.5" (inside diameter) belt -- Gatorback P/N 4060755 before the install. That belt was a snug fit. The pulley on the truck alternator is the same size as the stock alternator pulley, however the location when mounted is shifted ever so slightly outward, so it took a 76.0" belt.
4. Once I started the car up, my crazy charging issues seem to be solved. No more flickering lights, no more bouncing voltage needle. The needle hangs in the 13.0 - 14.0 range consistently. Problem solved.
Here are a few of my notes from the install:
1. The "truck" alternator lined up well with the mounting bracket and bolted in without issue.
2. Since the plug for the exciter wire is rotated a bit from the stock 105 amp alternator, I only have about a half inch of "play" left in that wire.....if it were rotated any further down it would require extending the line.
3. I have a 25% underdrive pulley and was running a 75.5" (inside diameter) belt -- Gatorback P/N 4060755 before the install. That belt was a snug fit. The pulley on the truck alternator is the same size as the stock alternator pulley, however the location when mounted is shifted ever so slightly outward, so it took a 76.0" belt.
4. Once I started the car up, my crazy charging issues seem to be solved. No more flickering lights, no more bouncing voltage needle. The needle hangs in the 13.0 - 14.0 range consistently. Problem solved.
Just an update -- picked up one of the AD244 alternators from a 2004 Express Van on ebay for $35 and installed it earlier this week. I coordinated the install with a front sway bar swap so it was great having the extra room to work on the alternator.
Here are a few of my notes from the install:
1. The "truck" alternator lined up well with the mounting bracket and bolted in without issue.
2. Since the plug for the exciter wire is rotated a bit from the stock 105 amp alternator, I only have about a half inch of "play" left in that wire.....if it were rotated any further down it would require extending the line.
3. I have a 25% underdrive pulley and was running a 75.5" (inside diameter) belt -- Gatorback P/N 4060755 before the install. That belt was a snug fit. The pulley on the truck alternator is the same size as the stock alternator pulley, however the location when mounted is shifted ever so slightly outward, so it took a 76.0" belt.
4. Once I started the car up, my crazy charging issues seem to be solved. No more flickering lights, no more bouncing voltage needle. The needle hangs in the 13.0 - 14.0 range consistently. Problem solved.
Here are a few of my notes from the install:
1. The "truck" alternator lined up well with the mounting bracket and bolted in without issue.
2. Since the plug for the exciter wire is rotated a bit from the stock 105 amp alternator, I only have about a half inch of "play" left in that wire.....if it were rotated any further down it would require extending the line.
3. I have a 25% underdrive pulley and was running a 75.5" (inside diameter) belt -- Gatorback P/N 4060755 before the install. That belt was a snug fit. The pulley on the truck alternator is the same size as the stock alternator pulley, however the location when mounted is shifted ever so slightly outward, so it took a 76.0" belt.
4. Once I started the car up, my crazy charging issues seem to be solved. No more flickering lights, no more bouncing voltage needle. The needle hangs in the 13.0 - 14.0 range consistently. Problem solved.
also the 4 screws that go "across the black area" connecting the front and rear of the alternator case can be undone and with a little force you can seperate the 2 halfs and rotate it around so the exiter plug and positive lug out to battery sit in a different location, just make sure you reseat the brushes in the alt if you pull it to far apart, again the videos on youtube of reassembling one will explain that better.
also the 4 screws that go "across the black area" connecting the front and rear of the alternator case can be undone and with a little force you can seperate the 2 halfs and rotate it around so the exiter plug and positive lug out to battery sit in a different location, just make sure you reseat the brushes in the alt if you pull it to far apart, again the videos on youtube of reassembling one will explain that better.
AlternatorMan on youtube is awesome. At one point I was considering replacement of the broken voltage regulator in the first AD244 I picked up.....my wife really enjoyed sitting on the couch listening to about an hour of the videos one night! Haha!
