This thing's driving me nutso.  [%|]It's an '85 Pontiac Parisienne (huge boat, like a Chev. Caprice).  A mere 58,000 miles on it.  I bought it from the dear old lady down the street after her husband died (his car).  Needed a couple of new belts & hoses to replace some originals that were ready for retirement after honorable service.  It ran great for months and then ... dead battery at the first cold snap. [:|] OK.  Old battery, low temp, didn't have enough juice at the low temp, bought a new battery.  

Bzzzt! wrong answer.  No charge from the alternator.  Check all of the connections.  Wire brush the main ones.  No more than .2 volts drop from the battery + terminal all the way to the alternator +Bat terminal, to the #1 terminal on the plug into the internal voltage regulator.  About a 1.9 V drop to the #2 terminal.  Expected, as that goes through a resistor according to the diagrams I've got (no ohm spec.).  Charge battery overnight, buy a new alternator, install according to instructions, etc.  Seems to work at first.  [:)]

Bzzzt!  Another wrong answer.  [:(]  Here's the kicker.  When the engine's running (and it runs fine, until the voltage drops too far), you can [i]hear[/i] the alternator running.  You can [i]hear[/i] the belt working to drive it.  Not slipping belt noise, driving the pulley noise, sort of a low growl.  Pull the plug on the regulator and the idle speeds up & the belt drive noise goes away.  It's putting out some amps, but they're not going into the battery.  The headlights light brightly, you can see them brighten slightly when the regulator plug is put back in.  The voltage is about 11.6 with the alternator unplugged, but never gets above 11.8 with it plugged in.  I can drive the car on just the battery & it seems to do OK in the daytime (no lights).  Turn on the headlights & the voltage just drops continiously & headlights get dimmer until the engine sputters.  Turn off the lights & it runs smoothly again for awhile, but the battery doesn't charge.  By now the voltage is low enough that I'm worried about geting home.  Made it so far, but the car's living on the battery charger.

I'm beyond my manual's advice & at my wit's end.  Anybody solved a problem like this before?

Helllllllllllp (fading away like a dying battery).

How bout a possible short to ground in the battery positive (obviously) cable? Is it rubbing anywhere? Corrosion or loose connection in same? Did your old alt check out OK or was it bad? You could have a new alt that's fried, stranger things have happened.

I don't know specifically about gm, but in old cars in general, mopar specifically, you might have a couple of problems to look at.
First, check the bulk head connections. The mopar cars are bad about that, and the volt/amp meters, dying and killing off the charge to the car.
The other thing is if the voltage reg isn't part of the alt, take a look at it and see if it needs to be changed, or if it isn't grounded very well.

I don't know specifically about gm, but in old cars in general, mopar specifically, you might have a couple of problems to look at.
First, check the bulk head connections. The mopar cars are bad about that, and the volt/amp meters, dying and killing off the charge to the car.
The other thing is if the voltage reg isn't part of the alt, take a look at it and see if it needs to be changed, or if it isn't grounded very well.

After the first battery didn't do the trick, I brought it back & swapped it, thinking it was fried out of the box.  Two (three if you count the old one) batteries, no change.  Thank you Advance Auto Parts.  Bought a reman alternator, it appeared to be no more than an idler pulley disguised as an alternator.  Got another one (thanks you RJ Strauss).  It's giving the symptoms described.  

Checked cables.  No visible rubthroughs, high (Meg ohm) resistance to ground.  Internal voltage regulator, no meters in the car, just an idiot light (it's off).  Main ground cable is right next to the alternator mount bolt.  No voltage drop across the connections.  The idiot light was on with the first reman alt, it's off with the current one.

Right now, the car's on a battery charger.  The battery's up to 12.8 volts.  This is with the ignition switched off.  If I turn the key to on, it drops to 12.2v.  Headlights on & drops to 11.8.  Off & back to 12.2.  I don't think that indicates a short, just the expected load.  

It just kicked over enthusiastically & fired right up.  Runs, idles fine.  Voltage running is 11.95, with the alt unplugged, 11.80.  Same sounds.  That reman alternator is putting out, but I don't know where it's going.

Nutso, I tell you.

Voltage regulator is inside the alt. and I doubt very seriously that the positive lead from the bat. is shorting/grounded because the car seems to run fine with the alt. disconnected.  so I would trace the brown lead off the back of the alt. (hot wire) and see where it is grounding out.

Thanks, JFP.  I can run my hand all along that wire & suspend it in mid air.  No change.  If only it was that simple.  The symptoms would certainly fit.  

This alternator is about 12"  away from the battery.  The wire is maybe 18" long because it runs down & around a little.  It's all loose & touchable.  No ground.

Keep trying guys, I know somebody has the answer.

Have you checked for a draw on the system with the engine off/key out/all lights off?

-Kc

trace it further!  Its fairly obvious that the drain is originating down stream from the alt.   I doubt that this could be the prob because of above,  but check the starter solenoid terminals something may have fallen against them.

OK I will give it a shot. I have been a GM service tech since 1980 (not bragging,just have seen a lot)
1. Are you using the old pulley on the rebuilt's? They wear out and will slip. The way to tell if the pulley is shot or slipping is to grab the fin's on the alt. and see if you can slip the pulley in the belt. If it slip's either the pulley is shot or the belt is not tight enough.
2. If you want to know if the alt. is really putting out enough voltage start the engine and disconnect the neg. cable at the battery if the engine continue's to run the alt. is working fine if it die's something is amiss.
3. Do a voltage drop test from the battery neg to the engine, from bat. neg. to the body, and to the frame. I have saw grd. problem's cause more demon possesion in car's than I can shake a stick at.
Hope this help's and I will keep monitering to see how you do.

Lee

Norm, one thing if for sure, you have a dead short. I have had one inside the starter solenoid before that had about the same symtoms. Sometimes a quick rap on the starter will help(couldn't hurt!!!), but most likely a new starter is in order. All hot wires come from or go thru the starter. May be the best thing is to take it off and have an auto supply store such as autozone check it out...good luck...fullclip

With all the real mechanics and shadetrees on this board, myself especialy, think of all the nailbiteing and hair pulling that will go on if norm doesn't report back as to what he found!!! The suspense is killing me!!!!fullclip

I jusr asked your question to a pro in the business and he said the very first thing you should check (just going by the limited info given)  is to be sure the bat. terminals are not backwards.    yeah, I know.   but shit happens....

Well, I fired it up & the battery voltage rose slowly to 13.42 volts.  Turn the headlights on & it drops fast to 12.4 and then a slow drop, maybe 0.01 every thirty seconds.  I pulled it up on a pair of ramps & looked at the wiring on the starter terminal.  It [i]looks[/i] decent.  Notice a little movement & [b]holy moley[/b], there's no cover over the torque converter.  I'm maybe ten inches from flying flywheel teeth.  I'd love to have a talk with the "mechanic" that maintained this old hog.  Have to fix that ... later.

The starter seems to work excellently when the voltage is up.  A short in the solenoid would draw current when the key's off, yes?  Key off: battery voltage is stable, same as disconnected.

I checked so many ground connections, I'll see them in my sleep.  Once it's running, everything works fine: all the little lights, electric windows, locks, seat.  I checked all of the above to see if they were not shutting off.  Each one will stop in mid-position.  

If I unscrew the pos battery terminal, the engine continues to run.  The idle rpm rises and I lose the "growl" from the belt driving the alternator.  I'll try the same thing with the ground terminal later.  Should be the same thing.

New pulley on the reman alternaor.  Not loose.

I'd describe this as a "three amp alternator"  It puts out enough to run the engine, but not enough for the headlights, too.  

Grrrr.  We'll find this gremlin yet.

Battery terminals are not backwards.  I don't think it would start if they were.  [rolleyes]

Next thing to try:  start it & disconnect the battery negative per Lee's suggestion.  If it continues to run, try the headlights.  Demonic.

I suspect you are barking up the wrong tree.  Likely another bad ALT.  Try this:  Measure voltage at stud on back of alternator when running.  Needs to be at least 13.8 if your meter is right (most aren't!), same at regulator sense lead.  Check at BATT.  Needs to be same.  With engine running a DC ampmeter (reasonable cost at autoparts store) will tell for sure what ALT is putting out.  Will be at least 35 amp capacity up to 100 amps possible.  With BATT charged, just a couple amps is normal.  To get idea of ALT capacity, turn on EVERYTHING in car and check - healthy ALT will output amps equal to load up to it's capacity while maintaining 13.5/8 volts.

An alternator can "sound" loaded and decrease engine RPM but put out no useful energy.  Cause is generally shorted stator or diode.  This is why I hate cheapy rebuilds - you may go thru several before you get a good one.  Damn site easier to fix my own!  Have them SHOW you it works on the machine in the store BEFORE you leave.

BATT should be about 12.6 fully charged, no load.  Check one hour after load or charge, check again at least 8 hours later.  Much change suspects possible load that is always on.  Unhook batt cable (negative OF COURSE!) and place ampmeter in series between BATT - and cable.  A few milliamps is max acceptable load with EVERYTHING off.  Battery that will not maintain stable voltage with cable unhooked has high internal leakage.  Quite often drops in rather sudden 2.1 volt step - definite bad cell!  Worse under load for bad cell.  Internal leakage can be uniform and slow.  May refuse to obtain normal 12.6 open circuit voltage as well.

Calibrate your meter!!  A new dry cell will be very close to 1.5 volts.  8 therefore is near to 12.0 volts.  A known healthy car works too, as batt should show 13.8 running w/light or no load.  Also possible to hook to BATT or ALT at parts store and compare to their meter but they are routinely wrong as well!  Keep talking to me, I eat these for lunch!

Mickey, I'm using a Fluke 77 digital.  Pretty decent meter.  Other cars measure 13.8x running.  Battery disconnected measures 12.8 after charging (on a charger).  Connected to the car, key off, it's still 12.8.  Overnight, no change, no drain.

First reman ($64) was just "not there".  It might as well be an idler pulley.  Second one fits your "shorted diode" description.  No AC current apparent.  

Out to try the disconnect & headlights trick.

Let's have lunch.

My GM products all register around 14.2 to 14.4 vdc across the battery terminals when running.  It's always well-regulated too, with very little dip when the accessories are energized.

More data.  Rechecked the pulley, no slippage on the belt.

Started it up, runs fine again.  Smooth.  Growly noise from the alternator drive.  Put the meter black lead on a chassis ground.  13.2 to 13.4 volts at the battery, alternator post and sense terminal (labeled #1).  Good connections.

Unscrew the negative battery terminal, voltage rises to 14.8 volts, the alternator is working.  Reconnect & voltage drops to 13.4 again.  Verrrrry slow rise when connected & running.  This fits with SWS's 14.4 volts (sort of).  Thanks.

Disconnect the negative battery terminal again, voltage rises again.  I turn on the headlights, voltage drops to 9.6 volts.  High beams engine sputters, can't see the voltage, back to normal beams, voltage up to 9.6 again.  Turn off the headlights, back up to 14+.  Reconnect the battery terminal and back to 13.4.  This alternator just isn't putting out the current it should.

Could it really be the second bad remanufactured alternator in a row?  Are they that bad?  It's not like I'm asking it to bring up a battery from deep discharge.  The battery is above 12 volts when I fired both of them up.

Sounds like the alternator is coming out tomorrow & going on a tester.  The place I bought it from burned their tester up the day before I visited them.  Terriffic.

Thanks all.  Too dark & cold to continue tonight.  I'll report again tomorrow.

Norm....mickey and nailbender have given you sound advice.......the alternator is a three segment device.....if voltage out is less than 13.8....it could have one bad diode and drive you crazy.....if it is under full load at least 13.8 as said.....here`s another one that has been showing up lately......green wires.....you really can`t see it unless you peel back some of the insulation.....but if the wire (cable) itself is green at the end..chances are it`s green all the way....creates MUCHO resistance...check the smaller red wire (alt feed) and the pos bat cable..check the junction block for the small red feed if equiped, for a corrosion problem or loose or short....move the bat ground cable from the alt bracket to anice clean spot on the motor...add a ground from engine to frame...anywhere convienient (asnailbender said)...good luck....there really isn`t much else to the gm system...if you have a draw it would seem to be easy to locate by your symptoms.....check everything you can see for clean tight grounds..............

Norm, I concur with what Mickey is telling you I figured you were using cheap Alt. but hate to condemn other brand's. I have a personal rule of thumb when it come's to part's, Buy original equip manufacterer new or rebuilt.
GM- GM part's or AC-DELCO
Ford- Autolite or Motorcraft
Mopar- Mopar part's

I have had any number of failures' from aftermarket rebuilt stuff.
One other thing when it come's to electronic part's ( ign module's, Computer's etc.) The people who originally designed and built it know more than the aftermarket does.
I know original is more money but you usually get a better warranty also.
One more thing if you hook up a battery backward's you will know immediatly due to some heavy duty arc welding and cable melting (been there very exciting)

Lee

Make sure you have the correct amp alternator for your car (I`m assuming you did already) but just to cover...if you have air and heated rear window, which that boat probably does, it should have somewhere about 95--100 amp alt maybe higher.....delco alts have the amp rating stamped right on them.....again good luck

I hooked a battery up backwards once, a long time ago.  Yes, it was exciting.  

The alternator is a 76 Amp, according to the catalog.  I haven't looked for a stamping.  Looks just like the one I took out.

I've connected the grounds (alternator frame to battery) with heavy clip leads, no changes.  The ground connection goes to the alternator mount that bolts to the block.  All of the starting current has to flow through those connections & the starter kicks the engine over very well.  I've wire brushed them anyway.  No change.

I'm presently thinking one or more bad diodes.  Tomorrow it goes on a tester.  Hard to believe two in a row.  We'll see.

Thanks again everybody.

B&G.  Agreed.  I know how they're supposed to work.  It's basically a three phase AC generator with three sets of diode rectifying (sp?) the current to almost DC.  The regulator changes the voltage to the rotating field to keep the voltage regulated in the outer windings.  Pretty neat concept, a real improvement over the older generators.  

I think my present problem is that I just can't believe I got two bad ones in a row.

We'll see.  Thanks again.

Believe it.

Lee

Norm G, your descripton of test confirms bad ALT.  One of the three phases is dead and amp capacity is very low.  Looks like two in a row!!

The 13.8 vs 14.4 volts is valid.  Voltage regulators are temp compensated and batteries vary a touch.  While 14.4 is normal, 13.8 can be too.  Depends.....  Less than 13.6 and it probably won't work.  Over 14.9 and trouble is at hand!

You have eliminated the green wire thing by the volt checks.  Amp rating of ALT doesn't matter at your point of diagnosis.  Accuracy of Fluke is excellent, I agree.  I just never know what guys are using.  Hell, I calibrate mine fairly often as well.

I just rebuild my own.  That way I know it is done right and what parts go into it.  Easy to figure out just which part went south and replace only that one, brushes and bearings if noisey, repack if not.  Darn site cheaper too!  More often than not, less than $20.

A modern alternator is a three phase AC variable frequency generator using full wave solid state rectification.  Current limiting is a function of stator resistance.  Voltage output is controlled by varying the current in the rotating fiel, passing through two slip ring/brush units.  Filtering of the resulting pulsating DC is via the storage battery which acts similar to a gigantic capitor.  A DC generator produces nearly pure DC with only a little electrical noise.  Trouble is, it is mechanically rectified and that is not ver efficent!!

I'll bet lunch it IS the ALT!

I won't take that bet!  I've changed brushes & regulators in the past, maybe a set of bearings.  

Pressing in new diodes is beyond my present capability.  And desire for that matter.  I paid for a good alterantor, dammit, & I'll get one out of these bums.  [:)]

One shoted diode or two open can REALLY destroy the thing's capacity!!  On old style, I keep several around and salvage parts as needed.  Throw it away when only a shell.  Same with starters, carbs etc.  Cheap parts!  Sometimes put one back together with ALL bad parts and trade with my junkyard for a couple bucks (they send to rebuilder anyway) or give to a buddy for core turn in.  Wonder what the apes think of THAT one?

See your point on new part!  Keep at it til they give you a good one.  Make them prove on the test stand in the store it IS a good one and save a little sweat.  They call the guys at Century gun monkeys - what do you call these ALT rebuilders?

You wanna rebuild one, I can give you all the details.  Newest GM is not as easy as they tried to make it difficult.  But it CAN be done!

Thanks again.

OK.  After another adventure-filled afternoon, it looks like I found a light bulb that lights up.  Third alternator from the same source works.  I put it in exactly the same way, with the same wires, same connections, same nuts & bolts.  This one works.  14.42 volts at fast idle, with or without headlights on.  Drove home in the dark and the lights stayed on for the whole trip.  First time that's happened in a few days.  14.4 volts at home.

I think we have a winner!! The guys at the parts place tested the oldie & said it had "bad" diodes.  Not failed open or short, just "bad".  I still think I'm going to watch this one pretty close for awhile.  Maybe even stick a little voltmeter on the dash, to augment the otherwise full compliment of idiot lights.

Thank you all for the help last night.  It kept me from going over the edge.  Whooda thunk, two "bad" alternators in a row.  And they looked so pretty! [rolleyes].

OT: Next time if you folks have an alternator problem, I remember a while back, you can hook up an oscilloscope on the output of the alternator and you can actaully see each of the phases on the screen, and see there is a bad diode somewhere.