1G Alternator? Battery? Other charging components?

[harith444]

I'm having issues with the volts staying up at idle. They will chill right at 14.1-14.2 when I'm driving, and when i'm at a light, I can hear my heater die down and the guage cluster dim out and the volts will drop to 11.8-12.6 and I have a brand new alternator, and a red top optima battery. There is a weird wire hanging down coming off the set of wires that goes to the ground on the alternator, and I've never known where that goes. If you have any info please let me know. Thanks guys!

 

[jazzyjay]

Are you running a underdrive pulley. What does you car idle at with the accessories off. I think the single wire you are talking about is for the power steering

 

[harith444]

My pump is gone so that maks sense. No underdrive pulley. Stock harmonic dampener. And my idle is at 750-812, so says the almighty logger.

 

[95blackGsTurbo]

A lot of our cars do this. The alternator isn't meant to deal with all the output needed at idle for gauge's and running the heater or defrost at the same time. What color wire is the one hanging down? I'm gonna take a guess at yellow?

 

[Froyd79]

Suspect the Alt. I just got a new one from the Zone (im done w/ reman stuff) and brought it back cause my volts were ok driving but sitting my lights were surging and voltage was dropping. Tested bad. Pulled another off the shelf that tested bad. Pretty much had to send me to another store to get a good one.

 

[harith444]

My alternator is good, and the one I changed out was good too, I had a hard time getting them to warranty that one. As for the wire, it is yellow. My defroster is always on, button doesn't do anything when I push it. Go dsm!

 

[95blackGsTurbo]

I beleive the yellow wire is for capacitor which would store voltage while driving, then when at idle it will use that stored voltage.

 

[harith444]

Where would the capacitor wire go? I'm completely clueless...

 

[toybreaker]

I beleive the yellow wire is for capacitor which would store voltage while driving, then when at idle it will use that stored voltage.

If the wire is yellow, and has a 90* round end, it goes to the power steering pump pressure switch on the pump housing.

The power steering pressure switch imput is used by the ecu to more accurately control the idle speed.

Cranking the steering wheel increases the pressure in the pump, which increases the load seen at idle. This will pull the idle speed down.

If the ecu "knows" there's going to be a load from the power steering pump, it can compensate with a little extra iac opening, and the idle speed doesn't change.

Edit; I've seen some harnesses that it's hard to tell the wire colors...they're all kind of a yellow..white..tan...

If you really want to know, you can check it with an ohmeter. Just go from the engine compartment wire, to the (unplugged) ecu harness at the ecu, pin # 5, (it's yellow/black there)

Also. check to make sure you have wires hooked up to the oil pressure switch, and oil pressure senders.

 

[dieseltech]

I beleive the yellow wire is for capacitor which would store voltage while driving, then when at idle it will use that stored voltage.

You'd need like a 5mF capacitor to be able to sustain voltage for any time period at idle . Capacitors used in conjunction with alternators or other voltage spiking systems are used to prevent electronic noise that can upset delicate components. If you've ever driven in a car that you can hear the engine rev up through the speakers, it's a good chance there is a capacitor blown, or a bad ground

EDIT: i forgot to add. Alternators have to have higher rpms to produce max power. I've seen many power curves for alternators and they usually produce max power around 5-6k rpms. Check your belt tension and feel the surface of the belt itself. If they belt is hard and appears shiny to the eye you should replace it. Good luck!

 

[harith444]

Me and a friend just changed the capacitors in my ecu. He had done it before on his gs-t so we jumped in and did it. I'm still having the same problem, the volts will drop at low rpm... I don't know what causes it to do that and wether or not it will have a prolonged negative effect on my car. I have had to warranty out the old optima battery I had and I'm afraid that it will ruin this one too if that was the culprit originally. I also cleaned my terminals on the battery today, and checked the positive wires and re checked all my BRAND NEW grounds. I have one on my frame to transmission, two from the negative terminal and one apparently running to the alt. Am I missing one? Any other ideas as to why the volts drop? Thanks guys!

 

[harith444]

Any other clues as to why I'm dropping volts with rpms?

 

[DGajre777]

Any other clues as to why I'm dropping volts with rpms?

You have a bad voltage regulator inside your alternator.

I had the same problem last month, the volts would go down to 11.8-12.0 at idle and not come up at all unless I was over 3000+ RPMs. I got a new rebuilt alternator from Mitsubishi and the volts go down to 12.0 at a stop light for 1 second but then it goes back to 14.2. It is the job of a voltage regulator to increase output when the RPMs are low, if it doesn't, then it is not doing its job.

Also, if you tested your alternator, they probably tested it at a certain RPMs, test it at idle and you will see that you have a bad voltage regulator. I hope this helps.

 

[harith444]

Ahhhhhhhhhhhhhh! I hate auto zone! I will have them check it in the car at idle. I'll update. Thank you!

 

[black92_tsi_awd]

One other thing to check is belt tension. My belt loosens up over time and cause the voltage to drop at idle due to slippage. At cruise rpms, I think centrifical forces tighten the belt enough to get the voltage back up.

 

[harith444]

Autozone tested it good, but I got a new one and it's doin' the same stuffWTF ... Could it be something on my car, other charging components?

Thanks guys!

Belt tension was good. As a matter of fact, could possibly have been a little tight. A little.

 

[spoold96tsi]

Such as DGajre mentioned, did they test at idle?

 

[harith444]

No, they didn't.. and he said if it's making 80% power it is good. I think autozone hires ex special olympics competitors. When he took the tester outside, it visibly read the 11.8 volts at idle, then he revved up to 2k and said it was good. What are the chances I have two bad alt from auto zone? Should I get my money back and buy another non auto zone brand?

 

[dieseltech]

You could do what I did and replace it yourself but then agian I've done a couple hundred of em :O If you don't mind spending the extra money take it to a reputable alternator rebuilder and have them install a regulator. Or if you cannot find one I may be persuaded to do it for minimal charge.

 

[harith444]

I fried my alt relay! Woooooo! Well I will pm you my number and we'll get a "quote" goin'. I think I might have fixed it, but I won't know until tomorrow when I get a new relay!

 

[harith444]

Changed the relay and fuse today, had the NEW alternator tested, and it came back good. I'm confused, 3 bad alternators in a row. I'm not sure what could cause it. Any ideas?

 

[toybreaker]

Your "problem" is a voltage sag at idle, with the lights, and heater fan on?

An alternators output is rated with two numbers, current, and voltage, both of which are rated at 2500 rpm.

Lets talk about the current aspect of this situation first.

The minimum hotel load to run the car, (fuel pump/ignition etc..) is around 8 to 10 amps.

The heater and lights together are probably around a twenty amp current draw.

At a curb idle of ~700 to 750 rpm, all loaded up, there's just no way the alternator can keep up with a 30 amp current draw. It will try and do what it can, but it just can't keep up. The alternator output voltage will sag, and with it the battery voltage.

This is not a problem with the car, it's just the laws of physics

The correct test method for checking the current out put on these cars requires a carbon pile/load test machine and a high amp inductive probe. The carbon pile load cables are connected to the battery terminals, and the amp probe is placed around the alternator output wire. The engine is started, and quickly brought up to ~2500rpm, and a calibrated load is applied. The minimum current output of a 75 amp alternator should be ~52 amps. (This test is a pita, and requires special tools.)

The next best thing is the little cheesmo testers that the 'special kids use at Autozone, etc. Just hook up the voltmeter, and inductive amp probe, turn on your lights for like 30 seconds to a minute, and then light up the car, bring the rpm's up to 2500, turn on the brights, and heater fan, and read the amp meter. If you've got more than 50 amps, you're good to go. Please note that the output current will drop fairly quickly, as the battery gets it's surface charge back, and it's voltage recovers.

Now, your question was about voltage sag at idle.

The alternators voltage output on these cars is very sensitive to temperature.

14.2-15.4volts @ -4*f
13.9-14.9volts @ 68*f
13.4-14.6volts @ 140*f
13.1-14.5volts @ 176*f

This means that a hot alternator puts out significantly less voltage than one that's just starting up from resting overnight. (This temperature compensation is because the engineers were concerned about excessive battery electrolyte loss/boiling the battery electrolyte out at elevated underhood temperatures)

So, hot motor = lowerish voltages=dimmer lights/slower heater fan speed.

Add in turbo heat, and the fact the alternator is only a couple of inches away, and you get excessive temperature compensation. I saw your other thread on an overheating issue, so I know your alternator won't ever have the chills.

If you run a voltmeter (I do ), you'll see this show up for real when the a/c compressor and radiator fans kick on, and the rpms drop for a moment. It's not uncommon to see ~12.5ish volts, worst case scenerio, all loaded up, at a slow idle, (especially after a bit of boostin., when the car tries to slooow idle )

Again, this is not a problem with the car, it's just the laws of physics

If I give my car an extra 50 or a 100 rpm at idle, it get's all happy again.

The alternator just can't put out all that much current at idle. The voltage drops, and begins to approach battery voltage, and that's that. If it drops to the 11's, then you've got troubles....

Please report back with the following information so we can see where we're at.

Resting battery voltage

Idle rpm? [very important], many times 50 or a 100 rpm will make all the difference.

Running, at idle, no load

Running at idle, loaded (turn on the lights and heater to high)

Running, at 2500 rpm, no load

Running, at 2500 rpm, loaded (as above)

Also, check the loaded voltage at the alternator terminal and compare it to battery voltage. It shouldn't be more than a tenth or two different.

This information will help us solve your problem.

 

[harith444]

Yes, with heat and lights on.

Resting Volts for battery. 14.2 cold and 14.0 at running temparture.

Idle rpm is 750-812 (logger)

14-14.2 volts running at idle no load.

Running at idle with a load. Lights, heater etc. 12.3-12.6

2500 rpm 14.2 volts

Running 2500 rpm loaded 14.0

My pops says those numbers are almost normal and from what you told me I believe so too. Not to be smart or anything, but does that mean other cars defy physics, or do these voltage regulators just suck. Our IS300's idle and voltage is barely effected when accesories are on. As for checking the alternator voltage under a load compared to the battery, I will need to update later today. Thank you once again toybreaker for the great post.


Also, that is wild how sensative these alts are to temp. During a pull I can watch volts drop to 13.6-13.8. Should I work on getting a heat shield fabricated for the o2 sensor housing?

 

[toybreaker]

Yes, with heat and lights on.

Resting Volts for battery. 14.2 cold and 14.0 at running temparture.

Idle rpm is 750-812 (logger)

14-14.2 volts running at idle no load.

Running at idle with a load. Lights, heater etc. 12.3-12.6

2500 rpm 14.2 volts

Running 2500 rpm loaded 14.0

My pops says those numbers are almost normal and from what you told me I believe so too. Not to be smart or anything, but does that mean other cars defy physics, or do these voltage regulators just suck. Our IS300's idle and voltage is barely effected when accesories are on. As for checking the alternator voltage under a load compared to the battery, I will need to update later today. Thank you once again toybreaker for the great post.


Also, that is wild how sensative these alts are to temp. During a pull I can watch volts drop to 13.6-13.8. Should I work on getting a heat shield fabricated for the o2 sensor housing?

I had to learn this the hard way.


I've had to deal with this on my own cars a few times. I live at 9200 feet, and it's uphill all the way to the driveway, so I'm well versed in the voltage/temperature output chart, as well as the low speed voltage sag issue these cars can manifest.

Not all dsm's do this to a noticable level, and that's why I asked you about the voltage drop from the alternator to the battery. The alternator wiring harness can get baked some by the heat off the turbo/downpipe. This makes the wiring insulation brittle, and it can begin to crack. The constant vibration can then begin to break the individual wire strands, because the wire flexes more in the sections where the insulation is broken. As the wire strands break one by one, the cross section of the wire still able to carry current slowly fades away.

This slowly diminishes the wires ability to carry current, resulting in a voltage drop from the altermnator to the battery. This will manifest itself as a large difference between the voltage, measured at the battery compared to the alternator.. (Voltage drop) Remember, the alternator doesn't actually know the battery voltage, it just knows the output voltage at it's output terminal.

Luv 2 rally or Gtm (our board electrical experts ) could give you a more definative answer about whats allowable for voltage drop, but I think anything more than a tenth or two of a volt drop (loaded) from the alternator to the battery will require further investigation.

As far as other cars ability to produce full current at idle, my wife likes to remind me that her car, (94 Nissan Altima, with over 275,000 miles), doesn't have any issues in that regard.

It's just a "quirk" of dsm's, especially higher mileage cars.

All those connections from the alternator to the fuse to the battery, as well as the grounds, get a little bit loose/dirty/corroded. This gives just a little bit of resistance at every connection. When you add it all up, you begin to see funky symptoms, like random voltage drops, and lights dimming/heater motors slowing down.

Simply disconnecting the battery, and removing and cleaning the battery terminals, and each and every electrical connection to bare metal can make an absolutely magical improvement in situations like this, and is always a good place to start.

I've noticed that a slightly higher idle (~800 to ~850 rpm'ish) seems to help a bunch.

You can also use the 90 amp Galant vr4 alternator as replacement for your 75 amp dsm unit. Since I started using them, I haven't had any problems with low rpm voltage sag.

Please, run a heatshield on your turbo/o2 housing/downpipe! The heatsoak from hot turbo/exhaust components at engine shutdown can really create issues with the wiring harnesses, alternator, and power steering pump. The exhaust system components are well over 1000*f, and that heat will just baste everything in the vicinity without the heat shields installed.

Sounds like your pop is pretty cool! You should be thankfull he is knowledgable, and willing to help. I learned more from my father and grandfather than I ever learned in school.

 

[harith444]

Thank you, I love the very informational and meaningful long posts. I am going to get a heat shield, inspect the alternator harness and go through and clean all of my connecting points when I get back from San Fran in a few days, then I will update. More than likely, from past experience of using your advice, this will remedy the issue. Good luck to all of you who are reading this for help. Thank you once again Toybreaker, your advice is greatly appreciated.