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2G Alternator voltage drops once car is warmed up

TurboSpider

Proven Member
223
16
Nov 2, 2015
York, Pennsylvania
  1. My old alternator was only outputting around 12.9 volts once car got hot and didn't seem to go up much more with rpm increases so I bought a remanufactured alternator for a 97 galant from advanced auto. Its a carquest premium. When you first start the car and it's cold it is idling around 1100 rpm and alternator is putting out 14.5 volts. As the car starts the warm the idle comes down to the set point in ecm link of around 800 rpm. Voltage drops to 13.5. Once the car is warmed up fully it goes down to 12.7-12.8.
Anytime the throttle is reved, voltage goes back up to 14.4 or so. I have upgraded the wiring from bat to fuse box, fuse box to bat, from neg battery to firewall, from negative battery terminal to engine to all 4 gauge wire. I also cleaned both terminals. Batteries resting voltage is 12.7 volts. The above voltage readings were obtained with no accessories on. If I turn the accessories on, the output goes even lower at idle.

I have done lots of searching on here and have seen many people saying this is normal and then again lots of other people saying it should be 14.5 all the time even at idle. I found in the alternator section of the service manual it gives different voltage output readings in relation to engine temp. With the highest temp range showing around 13.1 volts out put. That seems to sorta agree with the its normal. I also saw that advanced auto rebuilt alternators are junk from several people and that it isn't uncommon for people to have to exchange alternators several times before getting a good one.

Since I am using the 90 amp galant alternator I am wondering if it is regulated to not start outputting voltage untill 1,000 rpms because maybe the galant has a higher factory idle then a 2g eclipse? Maybe that could explain why it comes alive once the rpms come up a little?

Anyone else with a galant alternator have similar experiences? When my idle comes down to normal idle speed you can actually see the interior floor lights dim slightly and they get brighter when it's reved up. I have seen mixed things when searching but am starting to think the voltage regulator is not working. I also saw there is a generator relay, that I haven't really done anything with. The battery light does come on the dash with key on engine off although it glows dimmer then all the other warning bulbs

I have attached an idle log that shows how the voltage decrease as rpms come down
 

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chrysler kid

15+ Year Contributor
2,535
532
Dec 20, 2002
Mckinney, Texas
The alternator will send the voltage needed to recharge the battery. If the battery is already fully charged there is no need to increase voltage, and typically the battery will be at about 12.7 volts

If the alternator was sending out a constant 14.5 volts all the time it would likely cook or over charge the battery and damage the core.

From how you describe it the alternator is functioning normally
 

TurboSpider

Proven Member
223
16
Nov 2, 2015
York, Pennsylvania
I took it to advance auto and they tested it and said it was good yesterday. Although their test involved taking a reading of the battery with the car off, then starting car and reving it. Then reving it was a load on. It does seem like my battery has been maintaining around 12.6-12.7 and is not loosing charge.
 

chrysler kid

15+ Year Contributor
2,535
532
Dec 20, 2002
Mckinney, Texas
I work at an auto parts store, that's typically not how you test an alternator

Typically they test the battery first, have you start the car, and test the alternator while the car is idling

Basically the alternator tester puts a load test on the alternator, it creates a draw in current and the voltage regulator should respond and you will audibly hear the cars idle dip down as the alternator responds and puts out more power: the alternator spins harder and it drags down the engine idle to draw more power into the alternator

So maybe try the competing autoparts store across the street to verify results. You can also ask to take a picture of the results with your phone so you can see and remember the results
 

TurboSpider

Proven Member
223
16
Nov 2, 2015
York, Pennsylvania
I work at an auto parts store, that's typically not how you test an alternator

Typically they test the battery first, have you start the car, and test the alternator while the car is idling

Basically the alternator tester puts a load test on the alternator, it creates a draw in current and the voltage regulator should respond and you will audibly hear the cars idle dip down as the alternator responds and puts out more power: the alternator spins harder and it drags down the engine idle to draw more power into the alternator

So maybe try the competing autoparts store across the street to verify results. You can also ask to take a picture of the results with your phone so you can see and remember the results
Thats what I was worried about since my idle voltage seems to be what I am questioning and not when throttle is being applied as it comes up a lot then. I just figured the machine maybe tested it at idle for a while and then tested it again being reved. He printed out a little receipt thing that has all my results on it. I can try stopping at auto zone and see if they do the same kinda test
 

Sirius1995

Proven Member
208
32
Jun 15, 2021
Hattiesburg, Mississippi
The alternator will send the voltage needed to recharge the battery. If the battery is already fully charged there is no need to increase voltage, and typically the battery will be at about 12.7 volts

If the alternator was sending out a constant 14.5 volts all the time it would likely cook or over charge the battery and damage the core.

From how you describe it the alternator is functioning normally
this information is incorrect!

Healthy alternator should give 14.2-14.7V when car is running.
It will drop to about 13.8 when ac is blowing on max and high beams on when idling and climb back to ~14.5V when those are turned off
And this is a standard on cars! DSMs included
 

chrysler kid

15+ Year Contributor
2,535
532
Dec 20, 2002
Mckinney, Texas
this information is incorrect!

Healthy alternator should give 14.2-14.7V when car is running.
It will drop to about 13.8 when ac is blowing on max and high beams on when idling and climb back to ~14.5V when those are turned off
And this is a standard on cars! DSMs included

At an 800 rpm warm idle on a 20 year old car its not going to be putting out 14.5 volts. You can wish it all you want but its not happening. You'll see 13.2-13.5 range with ambient temps in the 80s

Im just stating what I typically see it idle
 

Sirius1995

Proven Member
208
32
Jun 15, 2021
Hattiesburg, Mississippi
At an 800 rpm warm idle on a 20 year old car its not going to be putting out 14.5 volts. You can wish it all you want but its not happening. You'll see 13.2-13.5 range with ambient temps in the 80s

Im just stating what I typically see it idle
that's incorrect, if you only get 13.2-13.5V on idle, you have worn out alternator, it's supposed to be ~14.2V
It's just how the alternator system works, ask any mechanic, I've been working on cars since a toddler and these were basics to learn
 

Sirius1995

Proven Member
208
32
Jun 15, 2021
Hattiesburg, Mississippi
  1. My old alternator was only outputting around 12.9 volts once car got hot and didn't seem to go up much more with rpm increases so I bought a remanufactured alternator for a 97 galant from advanced auto. Its a carquest premium. When you first start the car and it's cold it is idling around 1100 rpm and alternator is putting out 14.5 volts. As the car starts the warm the idle comes down to the set point in ecm link of around 800 rpm. Voltage drops to 13.5. Once the car is warmed up fully it goes down to 12.7-12.8.
Anytime the throttle is reved, voltage goes back up to 14.4 or so. I have upgraded the wiring from bat to fuse box, fuse box to bat, from neg battery to firewall, from negative battery terminal to engine to all 4 gauge wire. I also cleaned both terminals. Batteries resting voltage is 12.7 volts. The above voltage readings were obtained with no accessories on. If I turn the accessories on, the output goes even lower at idle.

I have done lots of searching on here and have seen many people saying this is normal and then again lots of other people saying it should be 14.5 all the time even at idle. I found in the alternator section of the service manual it gives different voltage output readings in relation to engine temp. With the highest temp range showing around 13.1 volts out put. That seems to sorta agree with the its normal. I also saw that advanced auto rebuilt alternators are junk from several people and that it isn't uncommon for people to have to exchange alternators several times before getting a good one.

Since I am using the 90 amp galant alternator I am wondering if it is regulated to not start outputting voltage untill 1,000 rpms because maybe the galant has a higher factory idle then a 2g eclipse? Maybe that could explain why it comes alive once the rpms come up a little?

Anyone else with a galant alternator have similar experiences? When my idle comes down to normal idle speed you can actually see the interior floor lights dim slightly and they get brighter when it's reved up. I have seen mixed things when searching but am starting to think the voltage regulator is not working. I also saw there is a generator relay, that I haven't really done anything with. The battery light does come on the dash with key on engine off although it glows dimmer then all the other warning bulbs

I have attached an idle log that shows how the voltage decrease as rpms come down
90amp Mitsubishi alternator should still give you at least 13.5V on hot day when hot, it's normal that voltage drops and variates a bit when it's +80°F and car is warmed up, so I do think your alternator is worn out but like I said earlier, turn car on and let it idle a bit, pop the hood and measure voltage from battery terminals, should be 13.9-14.5V when healthy charge, then turn ac on max and high beams on, measure voltage from battery with multimeter, and also from ground spot and aletrnator positive connection, if the reading is the same (should be 13.5-13.8V) you have normal charge on load on, if it's below that on battery terminals but good from alternator, your battery won't take the charge in, but if it's also below 13.5 from alternator try turning ac and lights off, measure again, it should almost instantly climb back to 13.9-14.5V, if it's slow or not moving back up, you need to replace or get your alternator repaired, also always make sure ground spots are clean, as well terminals and inspect wires between alternator to battery
 

ec17pse

Freelancer
5,593
2,893
Nov 1, 2008
London, UK, Europe
My old oem reman alternator did similar, it was fine when cold and when driving and warm it lowered the voltage. I had it tested and they found it was ok but it was not getting hot so i ruled it down to the rectifier most likely causing problems once hot, i swapped for a different alt and was back to being good again.

Its worth trying a new unit and seeing if the problem goes away as if it does then you know its an internal fault with the alt
 
Last edited:

99dsmer4g63

Proven Member
157
77
Sep 20, 2022
Shippensburg, Pennsylvania
Sounds like the way both of my 99’s acted. However I will tell you my experience and let you decide. You may want to do a search on the generator G terminal (pin #33 on ECU harness) and understand the way that it regulates the alternators voltage.
My car would cold start and idle at about 14-14.5v until it warmed up a bit. After it would be close to battery voltage. If driving down the road with light throttle it would also be close to battery voltage. If the TPS was higher than maybe 30% it would kick back into high voltage mode and be about 14-14.5v. Also if the idle switch was engaged while on decel it would engage high voltage mode.
I did not like how the blower motor and other electronics would react to the way the G terminal would control the voltage due to the ground being left floating and not floating. It made the car hard to tune with ECM link because the voltage would be different in different scenarios.
My battery is also located in the trunk for reference and have a newer advanced auto alternator I think 75 amps. It’s the one made for my car not the 90 amp galant. All the wiring to the alternator is factory minus the battery in the trunk. I ending up cutting the one wire on the 4 wire plug on the alternator causing my generator G terminal to not work correctly and always have the alternator in high voltage mode.
PLEASE do some research on the generator G terminal and understand how it controls the alternator. Since I have disconnected it my voltage is always 14-14.5v. I wish I would have done this 10 years ago to be honest. My car has never had a consistent voltage the way it does now and I absolutely love it. Some people say the alternator will not control voltage smoothly with out the Generator G terminal but I haven’t had any issues and would do this mod to any dsm I purchase in the future. Also not sure of your cars year but 99’s are a bit different because they don’t have a relay for the alternator.
Sorry for such a long post to read. Good luck but it sounds like your alternator is functioning the way the factory intended it to in my opinion.
-Daniel
 

Vegas Smith

20+ Year Contributor
5,035
2,906
Dec 2, 2002
Houston, Texas
A little bit of side note to go off of what previous post stated^, the alternator, to my knowledge, references a voltage source in your fuse panel (the sensing wire). Some people will actually switch the sensing location to, for example, the fuel pump power so that the fuel pump is always fed max voltage. The original sense location maybe have healthy voltage at the front of vehicle and this down-regulates the alternator while the fuel pump at the back may suffer with lower voltage. If you switch the sense wire to a low voltage location it can up-regulate the alternator voltage. Anyways..
 
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