Have an issue with my Alternator..

First noted I had some sort of issue when I had to jump the car this weekend. After a jump, it started fine.

Well, it became evident that the system is not getting 12 Volts - on occasion. It will work fine for a while, then dip down to 6-8 volts or so. I know it's not the gauge and it's losing power as the gauge lights and headlights dim some.

So first a question, I know with all the other GM's I'm familiar with - the voltage regulator's in the Alternator, right?

Also - usually I've known alternators to either pretty much work or not work - not bounce down and back up like this. Engine speed doesn't matter, it's random - and I'm not getting any belt squeal, although it's a bit on the worn side and could be slipping some..

 

It doesn't matter if the alternator falls out, the battery should still be able to hold a steady 12V for hours while driving. Both would have to be shot to make the voltage drop like that for real. You'll need to hook up a voltmeter directly to the battery to know what's going on, as the one in the car is not very accurate or reliable and goes via connections and switches, any one of which could be going bad. If you really only had 6V I doubt the ignition would be able to keep the engine running, and I also doubt the jump start itself had anything to do with this. Why did you need the jump start in the first place btw.? Check wiring and power distribution points, going from the battery and into the car.

 

Thanks for the reply

Originally needed to jump it because the battery was just dead - or almost.

The day before - it was fine. I thought at first, maybe it was a grounded wire (short) somewhere - but that doesn't seem to be the case, since it can sit for a day or two and start up just fine. I'm thinking it just wasn't charging the day prior to that and I didn't notice - it did crank a couple of times, but didn't have enough left to get the starter going long enough. (think my IAC is on the fritz so sometimes I have to hold the starter for a second or two, or just give it some gas to get it to fire up - nothing crazy like cranking for even 10 seconds, but it needs a solid spin to get it going). Initially, I thought I had maybe left the glove box open or something else while I was doing the O2 sensor and the Trans Mount.

I drove it again two days ago - started fine, ran up to the store and back. On the way up it was fine, on the way back, I started getting the 'voltage' loss and dimming lights. It ran fine otherwise - but I know, that's only until the battery is dead, lol.

For short trips, I'm ok - at worst I could walk home and get my other car or give a friend a call to give me a jump.

It may not have gotten to 6V, but it was definitely between dead zero and 12/13 (whatever it reads right in the middle, where it should be).

When I got home the other day, I popped the hood and checked (it was dark) the best I could - the alternator was definitely turning, no apparent belt slippage and I jiggled the wires around while the wife watched the dash volt-meter, no change it kept running low. I realize they aren't real precise gauges, but it's really given me no reason to think it's not ballpark right. I have a good Multimeter, so I'll check voltage at the battery too.

I checked the wires because the last thing I did prior to this issue was install a new O2 Sensor - it was a Delco, I avoided the cheapest ones.

I'd think maybe it's a gauge issue if the lights weren't dimming or the battery "dying".

Is there an easy way to check voltage from the alternator while the car's running with a Multimeter?
You think it's maybe just a dying battery? How can I determine which of the two it is? Take off the Negative lead on the battery while the car's running, right?

I'm wondering if it's just a dying battery - but even so, I can't figure out - while running, it's losing electrical power.

I'm thinking once the engine's going - the alternator should hold it fine - or does the circuit need that battery working just right too? I know it varied on cars - the older cars I used to work on, barely needed either one to run and they could most certainly run without a battery if the alternator's doing it's job.

 

Yes the voltage regulator is in the alternator. Check for power at the connector on the alternator both should have battery voltage make sure it has a solid connection. the heavier guage red goes to a fuseable link at the starter and the other tan/blk gets power from the cooling fan fuse. With the engine running and all electrical loads off you should have 13-14.5 volts or that neighborhood at a fast idle on the red wire from the terminal on the back of the alternator to the battery. Sounds like you might have either a dead voltage reg or a loose/bad wire or connection

I wouldn't suggest pulling the neg with the engine running you run the risk of a voltage spike wiping out the electronics.

 

Thanks for the good info, I'll check it out this weekend

I'm about 90% sure the battery needs replaced, although it may have a bit of life left in it. It seems to hold a charge ok. This isn't really a daily driver, so it might sit for a few days at a time.

Also, when I first got the car, it had no brake lights, I traced that down to the turn signal switch, but also noted along the way that the electrical system was in top notch shape - no novice meddling was apparent. I did notice a bit of electrical tape on the alternator ground, so I'll see what's up there too. I did try moving it around a bit with no noticable effect, but it won't hurt to take a peek.

 

You seem to know what you are doing, you just need to measure here and there with that multimeter. Also check to see if you have one of those pesky junction blocks in your car, they can easily develop poor contact. Good luck!

 

I try at least, mostly self taught out of necessity...

Just kidding, I just like to be sure of what I'm doing there, plus I don't have a ton of experience - yet - with Third Gen specifically. Most of the newer cars I've worked on didn't need much electrical system work. Not that '88 is newer (well... ) but it's not as old as the mid 70's I used to tear into all the time.

On that junction box - where would it be roughly?

Hopefully I'll find the issue quick. I'm thinking I'll just replace the alternator or have it rebuilt. The guy I bought the car from commented it was a 'new' one. Which had me wondering - not to knock any car parts store, but I know of some places where the alternators likely won't last as long as the junkyard's...

If I do replace it - what would my best target amperage be? A/C (not working yet) power windows, etc...

 

I'm in the same boat. Drops to 9/10V sometimes when driving along and the interior/exterior lights dim. Other times will fluctuate around.

The alternator is only a year and half old, so I'm not sure it's that. Haven't had a chance to play around with it yet though.

 

Same here... I really didn't get time to look at it this weekend. I did drive it a few times. On some starts, it was working perfect right off the bat, others it would be about the same 9/10 v or so.

Haven't needed to jump it again - seems as long as it runs ok for a bit, the battery will have a good enough charge to start the car. Checked the battery cables and alternator wires - they seem tight enough. The negative was a hair loose on the battery, but it's nice and tight now - didn't make a difference.

I think at this point, I may just replace it. If I find no change - well, I guess I'll keep both of them, lol. Depending on the core charge anyway.

 

Have you tried to inspect and follow the wires going from the starter and into the car? I'm leaning towards a bad connection here, rather than an erratic alternator and weak battery. (The batt would have to be weak to drop to that low voltage so fast, but then it wouldnt be able to start the car. It doesn't add up..) Just my 2-cents..

 

Actually... I think - maybe I'm dead wrong... but I think it's overheating. Not the car, but the alternator itself.

Here's why:

I've been trying to keep track of when and why it does it and have found this:

It works everytime on a cold start. But after a while it will dip down.
Noticed this over the last week or two.

Today - I've driven the car for about an hour and a half overall. Cold start - fine, all morning it was fine - the air was 'cool', and it didn't dip once on the way in.

I drove it to the bank at lunch - started fine, was fine on the interstate - but... it started dropping again when I sat in traffic a bit. I got going again - and it took a few minutes, but the voltage went back up again.

It only dropped once more on the way to the bank - I was going up a hill a bit slower and giving it more RPM's (bearing's heating up?).

But coming down the hill coasting, it shot up above 13 again.

hmmmmm

Went to the bank, got some food - it ran fine for a bit, took a slower route to start and it started dropping again. Got up to 60/65 - after maybe 2/3 minutes - it started working just fine again.

If I had to wager a guess - I'm thinking something, perhaps the regulator on the inside is just getting hot and going south.

I think - for now, I'm going to go ahead and replace that alternator and see what happens - at the worst, I'll end up with two good ones. Or two bad ones if something else is goofed! lol

I did check the wires over pretty well - couldn't find anything loose or overly corroded.

But yeah - I'm not sure why it dips like that, I'd think the battery would hold the current ok - but then... it reads the same low voltage when you turn the key to run - without starting or anything.

Although - you know - it could be an issue with a wire getting hot too - that's a possibility. Maybe I'll grab some new battery cables too, or at the very least, I'll take your suggestion and inspect that wire all the way down to the starter. Perhaps it's two issues and that's what's making it erratic like this.

 

Interesting phenomenon.. Yes it does seem (engine bay) heat related.. I've seen new alt's with loose internal connections (bolts), but it could act like a "thermostat" for several reasons.. I'll agree now it's more likely the alt itself, knowing that it drops to the same voltage as before starting (hopefully not lower than an actual 11-12V, measure this with your multimeter, see if it's almost the same in the cig. lighter as on the batt.). But it wouldn't hurt to check that starter wiring (though it requires you to get low and dirty), multiple faults have been known to happen. No need to replace battery wires I think, they would have given you trouble starting. Overheating would most likely take place at connections and show up on the insulation as melting/ discoloration.. Good luck!

 

Please go pull your alternator belt and get on the highway. I don't think it'll make it for more than 15 or 20 minutes.

I do agree a real voltmeter is needed to verify where the problem is. The bs gauge in the car is not all that accurate. As far as the voltage dropping, it will drop when the elec. fan kicks in, which sounds like what is happening while in slower traffic. I though my alt. was taking a **** last week, and turns out the gage is just a pos. Popped the hood with engine running, showing less than 12V on the dash, put a voltmeter on it, and was around 14. No problem at all.

 

Lo-tec:
1st. You're 1 day short of being 2 weeks late..
2nd. If your battery doesn't last more than 1/3rd hour worth of driving w/o charging then it's shot, or almost fully depleted to begin with.. You'd better have an easy starting engine if driving around with a battery in that condition then.. Have you actually tried this? If not then what's your reason for stating this?
3rd. What was the voltage inside your car, like in the cig. lighter then? Your single measurement says the generator works, but don't reveal any voltage drops due to potential bad connection in the wiring going into the car.. So who can say it was the guage being faulty? Experience have told us that they are inaccurate and unreliable, but I have yet to see someone post comparative measurements taken at the guage's pickoff point.

 

1st: I see you have solved his problem. I'm sorry for wasting your time.

2nd: I have done this. It's called throwing a belt.

3rd: I did measure the voltage at every fuse in the fuse block, and they were all well over 12V, nowhere near the 9 or 10 it was showing on the gauge. Short of pulling the cluster to measure the voltage there, I can logically call the voltmeter a tempermental and sometimes inaccurate POS.

 

1: I simply got annoyed with the bs attitude..
2: Ok, so then your battery had only 10-12% of it's rated capacity.. Frequent starts and short trips can quickly ruin a battery, I hope mine is in a better state..
3: Nice info, why didn't you just say so.. I'll agree with your conclusion, but still, can I deduct that you had around 1V drop in the wiring?

 

You two want to mud-wrestle outside or something?

-It's not bodgey voltmeter for either me or the OP, we both have interior/exterior lights dimming

-It's not the fans turning on, happens at highway speeds with low temp gauge, they also don't use nearly as much voltage when they are on

I don't know if me and Overcast have the exact same problem, but it's winter here and this morning it was dropping as soon as I started the car, outside temp about 60F (yeah not much of a winter, but hey) so not sure on overheating. I'm reluctant to go change the alternator straight way as the last guy to own this car changed it 18 month ago, maybe for the same reason.

 

Hehe, sorry about that, it's sometimes hard to keep the cool..
I'm convinced that a lot of batteries and generators gets replaced because of some bad connection somewhere.. I have yet to have such recurring problems with the generators in any of my cars, knock on wood..
I'm not looking at a wiring diagram right now, but how about the C100 (firewall) connector? Could that be a source of some of these problems? Most of the current used in a car comes from a single feed wire going through the firewall and into the dash. Any voltage drop there will spread to all loads in the car (exept the fans as they should be wired straight from the battery). That crucial feed wire (and connector) is hard to get at and so is easily skipped when looking for faults. If it were me I'd hook up a small temporary wire from the battery and into the car so I could measure the actual battery voltage and also the voltage drop across the feed wire. Nothing beats catching the offender in the act..
Hasn't anyone ever tried to find and fix the actual problem with the original in-dash voltmeter btw.?
Are the aussies also still boycotting the metric system? I'd have to use a conversion calculator but I suspect 60F is what we'd call summer, where I come from..

 

I had a similiar problem with my bird. check the fuse under the dash there is a fuse the other side of the circuit on the alternator.

 

exactly where was the fuse located

 

Just to update you all.. I think I was correct in assuming that the alternator was just getting to hot (prolly a cheapy).

I replaced it, and voltage has been perfect ever since.