What should high vs low idle voltage be?

[AuroraGirl]

so new alt is on, well, new-to-square, and the voltage when running at high idle is Pretty darn consistent at 14.7 even with load applied, it just dips and goes back. at regular idle, it seemingly dips into low 12s and goes into 13s, but perhaps the idle is set too low? I guess I just dont know what the "proper" idle voltage is. This is checked with digital volt meter at the battery, the gauge reflects this about .5 to 1 volt lower than meter but it could be the needle being bent in the gauge lol.

If the idle voltage is good or nornal i wont worry too much

 

[1987 GMC Jimmy]

I would say you want 13-14.2. 12.6 or lower is too low. I don’t see 14.7 messing anything up, not too many sensitive electronics, but some would argue that’s on the higher side of acceptable. I’m usually getting about 13.8-14.2 so that’s what I generally expect.

 

[Bextreme04]

I have my high idle set around 1400 rpm and low idle set at 700-800rpm... any lower than that and I get what you are describing

 

[82sbshortbed]

I have my high idle set around 1400 rpm and low idle set at 700-800rpm... any lower than that and I get what you are describing

High idle? Is that when choke is on and warming the motor?

 

[AuroraGirl]

High idle? Is that when choke is on and warming the motor?

when you set the choke on my 1406 the truck starts in a higher idle to warm up quicker, it can be dropped down at any time when desired by jabbing the throttle.

But what bextreme says makes sense, i didnt use a tach(I have a multimeter with a tach function) id bet ya my idle is sub 700. ill adjust that

 

[Bextreme04]

High idle? Is that when choke is on and warming the motor?

Yes, when you set the choke on a cold motor it steps it onto the high idle cam. Mine starts at about 900-1000 and climbs to about 1200-1400 once the choke pulls off. Slight tap of the gas pedal then drops it off the high idle cam and drops the primary shaft onto the idle set screw. The high idle screw is on the passenger side behind the choke on my 1980. Make sure when you set the high idle RPM it is on a cold motor after the choke has pulled off. Standard idle should be set on a fully warmed motor.

 

[82sbshortbed]

I thought that's what you meant but, didn't know how to adjust high idle. Thanks i learnt something today.

 

[AuroraGirl]

@82sbshortbed the edelbrock 1406 has two set screws, im not sure if you have a quadrajet or what but figured it important to note that

 

[Snoots]

Your alternator 'sense' wire should connect to the battery NOT over to the + post on the alt. I know this doesn't make much sense but the alternator 'looks' for the lower voltage to turn on. The best place to sense that is at the battery.

 

[82sbshortbed]

@82sbshortbed the edelbrock 1406 has two set screws, im not sure if you have a quadrajet or what but figured it important to note that

Qjet on mine. I pulled the eddy 1406 that was on it. No choke on it. Not that you really need one here in Texas. Couple of pumps in cold weather usually takes care of it. Lol

 

[AuroraGirl]

Your alternator 'sense' wire should connect to the battery NOT over to the + post on the alt. I know this doesn't make much sense but the alternator 'looks' for the lower voltage to turn on. The best place to sense that is at the battery.

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which of the three do you refer to?

 

[Snoots]

Red wire in the white connector. The brown wire goes to the 'idiot' light.

 

[Matt69olds]

Usually the “sense” wire is connected to a ignition hot power source at the fuse box. It’s usually a pink wire with black tracer. The idea is for the alternator to sense system voltage at the fuse box and adjust charging system voltage at the point it’s most important.


By connecting the sense wire to the charging stud on the alternator, the regulator isn’t seeing real system voltage. You may have 14.3 volts at the alternator, but factoring in normal voltage drop, you may only have 13.8 or whatever it may be. That may be why your reading lower voltage at the dash than at the alternator or battery.

 

[59840Surfer]

Too much generalization here.

There are a lot of factors that affect the output of the alternator, the biggest is the capacity of the alternator in the first place.

If you're comparing a 150Amp alternator to a 68Amp alternator, then idle output on the smaller one is going to take you to low voltage at idle.... but this is what the battery's there for.

The battery stabilizes the voltage and at an idle, and maybe at a long traffic light - and the lights are on, the brake lights are too, the blower motor is running either for the AC or the heater, the wipers are running, a stereo is on - [although a stereo isn't too much of a drag] ... you will more than likely see the headlights "flare" when you hit the throttle.

Then there's the temperature of the alternator and the battery 'cause those variables affect the output too.

I'd say again that if you are experiencing "flaring" of your headlights when you step on the gas after waiting for along traffic light, a long train at the crossing --- then the battery's maybe a little long in the tooth or just not up to the job too.

If you're not getting below 12.8 Volts output at idle and everything's warmed up and you aren't running a lot of accessories, then you're pretty much OK.

In the end it boils down to this: if you can start your engine, the battery and charging system are in a more-normal-than-not condition.

SOME flaring on older systems is a given, and shouldn't be something to worry about.

Idle speeds are kinda hard to state over the internet - 'cause you may have a manual transmission verses an automatic transmission - the stall of the convertor matters here too.

See? There's a lot of factors to consider --- but if you can reliably start the vehicle in the morning - or when it's hot - or after sitting a week - then I'd say you're in the ballpark of a balanced system.

 

[Raider L]

I was having a problem with my voltage gauge not showing enough voltage, 14.2 at idle but as soon as I got moving the voltage would drop to 13.8 which is okay. But when I would come to my first stop the voltage would drop to 13.3-13.5 and when I would start driving again the voltage wouldn't come up any higher than 13.5 and never come up to 14 anything.

So I called Auto meter and they didn't have any thing that helped other than make sure the wires were hooked up okay, which they are, so I figured that since the alt. was the original '74 alt. that has been rebuilt about ten times since 1981 when I bought the truck the field coil was worn out because I had replaced all the parts in it recently.
So I bought a new alt. and started over from scratch except I replaced the voltage regulator with a 14.6 regulator. Since all the voltage regulators I've bought over the years were dropping from my original of 14.4, and were all 14.0 now I assumed it was one of them inside the new alt.

When I cranked up the engine the gauge showed 14.0 volts. I got the volt meter out and read it right off the battery and it was reading exactly 14.6 just like the regulator I put in the new alt. I guess it's either the gauge is off after twenty-five years in the truck, a AutoMeter voltage gauge, or something else is wrong and I'd have to check out every wire to see where the problem is. When I rebuilt my truck I took every wire and crimped it and soldered it, scuffed the ground point, and made sure nothing was going to happen to it.

Is the alt. working? Yeah, but what's weird, like what else is new with this truck since Covid began, sometimes with all the weird problems the truck has begun to have, I think it has Covid; is the gauge now shows 14.4 when I start the truck and will fluctuate between 13.8 and 14.0 now.

The new alt. must have had to have time to "break in"? Never heard of it. It either works or it doesn't.