Okay I've noticed over the past few weeks that my volt gauge is sometimes very low.

I also noticed when I'm in park I have a searching idle, it goes up and down by about 150 RPMs, and when it goes down the volt gauge goes up. When the RPMs go back up the volt gauge goes back down.

On top of all that, I noticed that sometimes my blinker won't blink, then is when the volt gauge is down, sometimes into the red.

Today I stuck a Digital Volt Meter on the battery, and watched the voltage. With the car off it is at 12.68, with the car idleing it fluctuates with the idle, when the idle drops, it reads about 14.3-14.5, then the idle recovers, the volts go down to 12.8-13.2.

I then went one step further, I disconnected the battery while the car was idleing, battery still was reading 12.68, the volts at the cables was a steady 14.1, and my idle no longer surged up and down, it stayed steady. This made me question my battery.

I checked voltage at the alternator in all cases, it was the same as at the battery. I checked using the frame and alternator case as ground, and once again everything was the same as before. This proves to me that I do not have a bad ground, or connection from the hot side of the battery to the alternator.

The question still remains, is my battery bad, or is my alternator bad... or is there something else going on. I personally think it's the regulator in the alternator. Anyone else have any ideas?

Sorry it's a long post. I just need some input.

 

Oh no Mister Wizard,
I’m not sure where to begin!
Sounds like you have two different things going on; a big voltage drop and a little voltage drop that is associated with a change in RPMs.

I guess first I need to ask about the big Voltage Drop (VD). Use your DVM to measure the voltage inside the Cigarette Lighter (CL) the next time you see a big VD. Pull over to the side of the road; stick the Red meter lead all the way down to the back, center of the CL socket, then touch the Black lead to the outer metal part of the CL socket. Does this reading match the dash Volts Gauge?
Does turning on the Turn Signal (TS) cause the volts to drop lower? Next time you have this happen, try turning off the TS, then turn on the Hazard lights.
What else happens to the car when you see the Volts down in the red? Does the Fuel gauge change also? The dash gauges, TS, and ECM/Ignition all run off the same voltage supply “branch” of the fuse block (but thru 3 different fuses). The hazard flasher is supplied by a different branch. The TS flasher needs a minimum voltage level for it to work.

Now let’s talk about Alt output voltage at idle. You say in your post, when the RPMs slow down the voltage goes up. This is backwards of how Alternators work!
At idle, lower speed = lower voltage. Higher speed = higher voltage.
Please please please double-check you readings.

FYI: You should get the same voltage readings at the CL as at the battery.
I need more info:
Is it only a problem when the engine is warm? Only in Park? What about in Drive with foot on the brake? What about in Drive with foot off the brake and car rolling slowly?
What happens in Park when you turn on the headlights or the A/C?

Check your battery voltage after letting the car sit for a few hours, 12.5 volts means it is holding a good charge.
From what you describe, I think it is good.

The Alt also sounds good so far. But bad brushes or flaky rectifier diode can cause some strange symptoms.
Here’s a trick: Use your DVM to measure the amount of AC “ripple” (noise) the Alt is putting out. Just set the DVM to AC Volts and measure just like you did when checking voltage. Watch this for about a minute to see if the amount of ripple is constant, or if it changes greatly over time.

What I think is happening is that the TPI ecm is changing the IAC setting for some reason which causes the RPMs to change.
Is the dash Volts gauge reading low when this is happening?
Do you know someone who has a Scan Tool to pull data out of the ECM?
Is it storing any fault codes?

PS: Nice looking car, how long have you owned it?

 

It's not so much a voltage drop, but it just stays low, right above the red on the volt gauge, turning on things makes it drop lower. This includes TS, pressing the break pedal, turning on headlights. The gauge does not match my DVM exactly, but when it is in the red I am seeing about 11.3 volts at the CL. Hazard Lights flash fine when it's in the red though. I don't notice the fuel gauge changing, nor the oil pressure gauge.

I double checked the alternator output, when the RPMs fall, the output goes up, to about 14.5 volts. When the RPMs recover the voltage goes back down, to 12.8-13.2 volts.

Problem happens when the car is warm. The surging only happens in park, when I put it in drive the idle drops to 750 and stays there. In park when I pull the cables off the battery the idle stays steady at 850. As I discovered right now, when cold I only get a reading of 11.8-12.3 volts at CS and Battery at idle. If I turn anything on in park, the volts drop lower.

The dash volt gauge reads low most the time, when the RPMs drop at idle, the voltage guage reads a little high (between the red and the 13). It is only a split second when the RPM drops, then recovers, then it will stay steady for about 10 seconds then drop again, then recover. I know it sounds weird that when the RPMs drop the Volts go up, I take it as the Alt is putting a load on the engine, causing RPMs to drop, yet putting out power. The IAC in the ECM stays steady at 45 counts, then when the RPM drops and the volts go up, it opens to 53 counts, then the idle goes up and it drops to 38 counts, then returns to 45 counts, only to repeat the process again. The idle is dropping before the ECM moves the IAC. I have no codes either.

I believe at this point, since I just tested it cold, that my Alternator is only working once it warms up, and even then is not doing it's complete job. It seems to be either charging hard(13.5+) when the RPMs drop, or barely charging (<13.5) at the steady idle.

Sound about right? Guess it's time for a new Alternator.

I got my car in October of 2003, so I've had it about 5 months.

 

As the alternator itself kicks in and out, the load/unload will cause the rpm to fluctuate usually faster than the idle control can recoup.

 

Before condemning an Alt, check the voltage supplied to it on the Brown wire at back of the Alt. Alternators need a supply of current (voltage) to generate the internal rotating magnetic field that it uses to produce alternating current (AC), which is converted to direct current (DC) by the diodes. Once it starts generating it own current, it no longer needs an external supply.

Your Alt might appear to be weak because it is not getting a good voltage supply from the Brown wire.
Weak electronic components are usually made worse by heat, not better.

You can replace it if you want, they do have a limited life span, but I would be very surprised if it is the cause of all your symptoms.

The Cig Lighter should have exactly the same voltage as the battery. If not then there is some resistance somewhere (assuming good grounds). The most common problem on our cars is the big starter lug where the fuse links and + cable all connect. Disconnect one of the battery cables, then crawl under the car. Remove the nut and all the wires, clean the lugs and reassemble.

 

Forget about the idle problem, most likely it is being caused by the gen load changing. 87 , I think had the CS130 generator. 3 things are common for your problem. First, brushes severly worn can cause intermittent contact with the rotor slip rings causing intermittent charging. Second, there is a rear cover that is held in with 2 push pins. Try to remove it and look at the solder connections to the diodes. There will be 3 heavy wires from the stator to the diode pack, sometimes the get so hot the solder melts and you intermittenly lose a phase. The last and probably most common thing is the diode pack itself. The Delco rectifier or diode pack uses a rather funky way of forming the diode connections. Instead of the press type they use a flat copper strip to connect to the diodes. It is very common for the copper where it connects to the diodes to pull off the diode junction causing erratic output. Never ever take the battery off the alt when running, the resulting voltage spikes can easily damage the regulator or in the worst case if the gen full fields fry the ECM and any other electronic components. If the batt is at 12.6, thats about as ideal as it gets.

 

Parts store said alternator is good, watched them test it, the machine said pass on everything. They then told me to bring my car back and let them check the battery and charging system. They checked it, said it is charging okay, but the battery is low. I don't understand this, as I drive it every day, more than an hour a day most days. Why would the battery be low?

I charged it over night with a charger, the charger slowly dropped to 0 amp input, which I assume means the battery took the charge, as all other batteries I charge do that when they are fully charged.

Anyways I drove around on it today, the gauge started way up, above 13 when running, but slowly it dropped back off (by slowly I mean over hours) I went to the gas station, gauge stayed above 13, came home... few hours later went to school, gauge was then a little below 13, came out of class, went to my girlfriends, battery gauge was now getting closer to the red, but not touching the red yet. On my drive home the gauge sat at the red the whole way. I know it's not completely accurate, but it does give me a pretty good idea of where my volts are.

I have yet to check all my connections, I did make sure the cables are on the battery and clean. I checked the ground, both by resistance and voltage difference, all looked fine.

I need a little help with wiring... there's the black thick gauge wire, goes to the Starter terminal correct? The hot side of the battery goes to the Starter Terminal also correct? Then there's a brown wire that comes off the ignition?

Basically if someone could tell me what all the wires do and where they go I would be happy... my Chiltons manual has diagrams but I can't really read them too well.

I'm not so much worried about the idle, as I have been told that it will vary slightly as the alt kicks in and out.

Battery just doesn't seem like it should be bad, the date on it proves it is less than a year old, and it's no cheapie (Die-Hard Gold).

Any other ideas?

 

A spin up bench test is not a good indication of the alt's condition under heavy load. I ran into this with my daughters 99 cavalier. She was at school and was calling me up saying the gen light was coming on. I would check it on weekends when she was home and the batt was always low, I charged the battery and tested gen output and was fine. What I found when I opened it was fairly common with GM gens using the factory diode pack. Where the copper connects to the different diodes in the pack it is VERY common to develop an intermittent connection. With heat it eventually opens the diode connection, then the gen full fields until the reg IC gets too hot. When the IC reaches around 280 degF it essentially shuts down giving little or no charge. I suspect thats what going on. Any doubts, take it to an alt shop if you don't want to gamble on the price of a new one. Chances are he'll tell you the same thing and maybe fix it cheaper than replacing it. Sorry to be repetitive but I would wager the gen is bad.

 

The ends of these diodes.. those are the ones under the little black plastic cover on the end of the alt? Could I just hit them with the soldering iron and a little bit of solder, see if it tightens things up a bit? Also how do I get the pully off the Alt, I tried but couldn't get it loose. Is it left handed thread or something?

 

Under the plastic cover are the connections from the diode bridge to the 3 stator wires. Take a close look at them, if you see the solder melted and a kind of blob chances are the bridge is gone, and no once the diode juction burns or separates you will need a new bridge. They run about $30 at places like NAPA or online assuming you want to fix it youself. I have seen a few where the wires got hot and one section of the stator is intermittent. If the solder joint look overheated you can try to resolder them. Use a gun as opposed to a low wattage iron and 60/40 tin lead electronic solder. A good joint will look shiny when you are done. You need to seperate the case to replace the diodes.