'91 Z28, 305-TPI, 61k miles;

So, the other day I started to notice the gouge cluster volt-meter reading down below 12 on the way home from work. Luckily... I made it home from work, but just barely, I figured my alternator had gone and charged the battery up overnight to at least get to and from work the next day. When driving to work the next day, everything read fine. Gauge cluster read ~14V and all was fine. Seemed weird, but still figured the alternator was "going" and would need to be replaced soon.

The next few days were the same and today I had time to test/debug. I hooked a meter up at the batter terminals and drove it around... with A/C, lights, radio, etc. it was sitting at about 13.7-13.9. I drove about 15-20 minutes, made a stop or two and then headed home. Just as I'm getting home, the voltmeter slips down in to the 12-12.3 range... so now its pulling from the battery. This must have been what happened the other day when I almost stalled out driving home.

Debugging in the garage after the drive, I turned things on and off... and noticed that it seems the electric fans behind the radiator are what finally drives the voltage down into the twelves. Idling and with A/C on, the fans eventually will both kick on and show the low voltage at the battery. I did not try revving the engine up to see if the voltage recovered. Since this condition had happened while I was driving when the original problem occurred, I assumed it would be the same issue either way.

The question I have is, is this expected... or is the alternator starting to go and not generating sufficient voltage under load? It is not the original alternator, but the current one has been there for many years. I didn't have any trouble driving all winter, but the A/C was recently repaired (leak) and coolant added, and a stuck thermostat recently replaced... so the fans running when they're supposed to may be a new condition.

 

Alternator could be weak. Are you using a factory alt with upgraded fans and additional electronic current consumption?
You may want to compare alternator output voltage with battery voltage at the same time to see how bad the drop is, which will indicate whether the alt is just poorly keeping up or there is some issue such as grounds...

Obviously check your grounds, engine to chassis, chassis to battery, engine to battery, alt to engine bracket, make sure everything is good. Not just visually, sometimes they are corroded, you may need to pull and twist a bit to see if it feels 'crispy'.

Another thing is alt hates heat, the hotter it gets the worst the output. Heat adds resistance.

And finally the way I would ultimately diagnose this issue if all the cables are good, You'll want to see what the resting battery voltage is after the car is shut off for a few hours.
When you first shut off the vehicle battery electrolyte will show a 'surface charge' higher than actual battery charge. But after 3-5 hours it will settle down.
A fully charged typical lead acid is 12.65v. Most alternators will not charge that high however, usually you will see maybe 12.45v or 12.55v or so "fully charged". But anything less than 12.45 or 12.35 I would start getting worried the alternator isn't doing a good enough job. In almost all cases if you want max battery life and fully charged it will require a plug-in charger for a few hours say 2 to 4amps or whatever after you drive for a few hundred miles. Just typical automotive bs

 

• I'd run the alternator down to a local parts shop and have it tested. They can load it up and get a good readout. Stock GM fans don't draw huge current, but the Ford fans sure do.

 

we know it works. parts store will say it works. they have no way to know how much current your electrical system draws, their 'load' might only be 70amps and he could be using 100 or 120amps. Unless it is severely degraded it will produce some effect voltage raise and sometimes 13.4v is good enough to pass a load test where the battery obviously needs more like 14.5v to fully charge. Obviously to me, if you intent to remove the alternator the only solution is to replace it with a brand new one. Not a re manufactured unit and just keep the old one that will also produce more amps. Not a reman unit either. And No way i would re-install the old one, so just assume if it comes off you need a new one to put on.

 

I'm just curious which Model Alternators are you finding new?
Also what do you define as new?

For example, I rebuild the 230 and 244 Series Alternators in two different ways:
-All new Parts excluding a Media-Blasted Case from a previously used Alternator (I also offer Powder Coating) (I consider this to be remanufactured).
-All new Parts with new Billet Case Halves (I consider this to be new).

 

For random people with limited electrical skills a quality name brand new alternator from rockauto will give a somewhat higher chance of success than any of the other options.

NEW is no guarantee of anything but rebuild by anybody but yourself after years of experience successfully is a much higher risk than usual, statistically I would infer.

The main point is: He determines amperage requirement and suitable cable flow, followed by correct output alternator new from OEM style manufacturer, with a warranty

while keeping the old one just case the replacement falls apart in short order or some other issue, at least nothing changed

Electrical in this case with respect to measured voltage is like water flow, a reliable means of determining whether enough pressure is being pumped in gives the correct response solution

 

Thanks for the feedback guys. For some additional details... Camaro is 95% stock, original electric cooling fans. Only thing "upgraded" is the stereo (straight replacement, no AMP or other additional) and I plug in a dashcam system into the 12v cig. lighter.

Alternator was a rock-auto replacement for the time is was bought ('NSA') and was new, not reman.

KingTalon, if the alternator was "keeping up"... I wouldn't see the drop into the low 12V's with the cooling fans on would I?

I'll check the wire connections and grounds, though I'm not seeing any other electrical anomalies. In the end... I guess an alternator replacement isn't the most costly or challenging replacement and may be worth it either way.

 

When I revived my car, the alternator "worked". It would be in the high 13v like yours to start, but after half an hour of driving, it became inconsistent and volts would drop below 12v. Sometimes it would come back up, but based on the fluctuation of the gauge, it was struggling. I replaced it with a new AC Delco unit of the correct output for my car and volts are much more consistent now. Given that stock replacements are relatively cheap, and installation is quite easy, might as well swap it out for a nice new unit.

 

Sounds like the diode trio might be on the fritz...maybe, but also check those cables for looseness..

 

[QUOTE=allaneyre;6471606]
Alternators are hit or miss. Some reman are good, some not. Some new are good, some not. There are too many individual components inside and too many manufacturing process to have any inkling idea from the outside at any year, point in time, manufacturer, etc.. whether its 'good' or not. You can only try. But they are cheap enough and easy enough to change and the new ones tend to be superior statistics wise which is why it boils down to that option for most generic replacements.

Its like water pressure, so yes and no. If there is a kink in the hose you won't get but a trickle on the far end while the feed is plenty of pressure. Thats why I said measure at the alternator output lug and compare with battery. There is always some pressure drop (voltage drop) along any length of pipe (wire) but it should not be significant enough to raise alarm.

Sometimes it takes two or three but eventually get you get a 'good one' and it may last 5 10 20 years

 

when one of those diode goes bad it causes the A/C power to look like a ground and that will light the bulb in the dash

he probably isnt having a full on alternator failure with the dash bulb coming on and all that yet or would have mentioned it

 

Its got a volt gauge. Why would it need the bulb?

 

Bulb provides resistance which runs the alternator. Remove the bulb the alternator won't charge. Unless you install a resistor or some other shenanigans or a ECU to control it directly.

 

Bulb is only used with idiot lights, car has a gauge though.

 

it took me 10 seconds to find a service manual free download
and 25 seconds to look this up

Next time, try that instead instead of guessing when you are trying to help people, you can't just guess


The bulb is an integral necessary part of the charging system. Part of voltage regulation and diagnostics. Not an 'idiot' light. How does the bulb know the difference between a massive current draw which pulls voltage down to 12v and a dead alternator? It can't just by voltage alone, there is no way to tell the difference just from a gauge. Battery voltage during heavy draw 12v: bulb stays dark because alt is good.

 

Yeah, i seen that, dont look like the f-body schematic. https://www.zinref.ru/avtomobili/Isu...nglish/408.htm

 

GM does use a hidden 194 bulb, due to the resistance it provides, to operate the alternator.

You can see this in the wiring diagram for the digital cluster, which does not have a battery light but a digital readout:

 

See yourself
https://www.allcarmanuals.com/factor...et-Camaro.html

It doesn't matter what kind of car though because all pre-computer controlled alternator vehicles era used the same exact alternator output control via dash bulb resistance
So I knew without the service manual, its either ECU or BULB controlled

The BULB is the diagnostic and relevant alternator control point,

the dash volt meter is the IDIOT light

 

Other than for resistance. What good is it if its hidden? Although the OP has a 91 camaro (w/ gages) where would the bulb be, if any? Cause ive never seen a "bulb" in a 3rd gen cluster. Unless it had idiot lights.

 

 

It's there entirely to operate the generator. The digital volt meter is the indicator to the operator to the status of the charging system, like it would be for a non-digital cluster with an analog voltmeter.

On the non-digital cluster there is a resistor to accomplish the same thing instead of the hidden bulb:


Again, it's there for resistance on the circuit to activate the charging system. It is not there to provide any indicator to the operator.

To clarify, I used the digital cluster as the reference since it was a better indicator as to how the circuit works.

 

Thats a good question, many people remove the bulb in their car and replace with a resistor.

Makes me think there might be a way to see the bulb.

How about this?
https://www.thirdgen.org/forums/carb...ml#post5612565

 

No, that Choke light referenced above is an actual warning indicator on early ThirdGens that is visible to the operator. That light is also on early digital clusters but was later replaced with the Security warning indicator.

This hidden generator bulb is actually hidden and not in the warning lamp indicator row. It's actually behind the multi-gauge readout (Oil, Temp, Volt) but is blocked by the overlay so it should never get through. Besides, there is no indicator for it so no one would know what it is if they could even see light from it.

 

Oo i like that. A secret bulb

What a mysterious way to run an alternator though

I don't know much about thirdgens, just general car stuff that applies to all cars, but I won't forget that thanks for sharing. Never seen a secret bulb before

 

LOL!

Don't keep bringing up all the wonderful Design Engineering screw-ups like that Choke Indicator Light fiasco.


LOL!

 

I Was just outside lighting off some home made fireworks and got to thinking, between loud noises in the silence between my ears, I wonder if they kept the bulb because the design was proven and reliable. I wonder if someone said "lets just use a resistor" but another engineer was able to show a way that could go awry or an issue with future consequence. I wonder what the issue with a resistor is? Bulbs dissipate energy - resistors dissipate energy. Bulbs turn some of that energy into light and resistors do not unless it gets red hot I guess. Maybe the bulb is simpler to replace, in event of alternator issue with current burning up that wire? Bulbs are not more reliable than resistors? Maybe back then, they actually were in a mass production sense, I don't know, just thinking to myself. Maybe they couldn't account for the mass production quality of a particular resistor value "silver" or "gold" , or maybe it wasn't possible to design something on-board with enough heat dissipation reliably. If you think about it, resistors are actually annoying to wire in-line, most are soldered to a board, but there are hundreds of others soldered in- why not this one? It must be something to do with the quality, reliability, or simplicity in nature.

 

Oh I just thought of something. The resistor could be 'working' while the bulb acts like a switch open 'not working' thus more efficient. Hmm.
Well no matter, its all ecu dutycycle controlled these days.