radwebster

ok, my charging system is basically crap. when the motor warms up, sometimes the volts drom from the usual 13-14 to about 11.5 to 12 and keep dropping(indicating that the alternator stops charging). the interior and exterior lights also dim to accompany the drop in charge.

generally, when i give it a little gas to anything over 700 rpm's, the charging will kick back in and the lights will brighten up again, but it almost always drops back down when i let off the gas. it's been like this since i got the car 2 years ago, and this is the second alternator thats done it.

i pulled the harness for the alternator and a/c compressor out from around the front of the motor, as i believe that the heat from the motor has somehow, over the years, damage one or more of the wires. the volts only seem to drop when the oil temp gets to about 170 or so. and its fairly random too, as if i let it idle for a bit when its hot i can see the volts drop off for a while, then sometimes kick back on, or sometimes just stay off even when i give it gas.
on hot days last year it even got to the point where the voltmeter was showing about 10.5 volts and the motor would stumble a bit at idle. when it cooled off, it worked fine.

so my question is: is there a way i could just hook the alternator straight to the battery in addition to leaving the regular harness alone?
the voltage regulator is contained in the alternator as i understand it, so couldn't i just run wires directly from alt. to batt.? or, would it drain the battery when it was off?

this is the major problem with this car, and it drives me nuts because i can't solve it. i don't care about originality or looks under the hood, i just want it to run correctly. thanks for any help

bogus

You may be onto a fix, but you would want to repair the harness correctly, not half-assed. If you do this wrong, it will nuke something.

SAE changed the requirements for wire compound starting with the 1991 model year. Prior to that, wire was subject to failure of the insulation. Heat, chemicals, etc, will cause the wire to break down.

I would replace with new wire and do it right.

You will need to get the schematic apt for your year (which you didn't list in your post). The best source for this is Helm, www.helminc.com. They produce the factory service manuals for GM.

jfb

The alternator is already connected directly to the battery, the alternator output that is. The voltage regulator is turned on by a contact in the ignition switch. It is possible that the previous owner installed a smaller pulley on the crank damper for reduced parasitic drag and a few more hp. This would make your alternator run slower rpm at idle and cause it to not charge. My 87 is stock and charges at idle and maintains 14.7 volts cold and 13.7 volts hot (actual battery voltage, the dash voltmeter reads 0.3 volts lower due to drop in the ign sw contacts). Unless you have an unusually high current drain or a small crank pulley or larger than normal alternator pulley, your alternator should maintain 14.7 v cold, 13.7 v hot. Also, you could have a discharged battery and I would at least put a battery charger on it for a full day. A discharged battery will draw a lot of current from the alternator and at idle the alternator cannot generate its rated current and its voltage will sag under a high current load. You can tell the state of charge in your battery by measuring its terminal voltage after it has sat idle for a couple of hours. 12.0 volts and lower, discharged. 12.9 volts and higher, fully charged and linear in between (example, 12.5 v, 50% charged).
I don't know why you should be worried about the idle volts when you don't spend much time idling when in traffic other than your idle battery volts clearly shows a discharged battery. Try charging the battery all the way up and keep it charged up if you don't drive your vette very often, batteries self discharge 1% every day! Don't use the alternator to charge it up!

radwebster

i am sorry bogus, it is an '84. i also have the factory service manual on my computer, and from what i could tell, the harness runs into the firewall about midways behind the motor, which would be a huge project to remove and replace will fresh wire.
like i said, i pulled the harness from around the front of the motor up to the wate temp sensor on the side of the block. i was playing with it while it was running to see if i could change the charging when it dropped, but the results were inconclusive.

to be honest, this car is one of the biggest pieces of s%&t i have ever seen, and i really am not concerned about the original look under the hood. whatever will work is what i will do. thanks for the response

and jfb: i worry about it because its not always at idle, like i stated earlier when its hot out it doesn't begin charging again consistently or sometimes at all. i am worried about being stranded because of this, i would love to just get it fixed.

DRAKEFAMILY2

I think Summit has a one wire alternater that might solve your problem. I believe the only wire is from alternater to battery.

redwing76

I agree with this post and the one from Bogus.
Where did you get the "new" alternator?

yellowlust

And you're 100% sure that all your grounds are solid?

azzkikr

I've had my "unfair" share of alternator problems myself. Sounds like an alternator problem to me. I've even bought a brand new alternator that was defective... when I returned it - I made them test the next new one before taking it home, you guessed it a whole batch of defective alternators. The fourth one finally worked. Well, after "pimping" my engine compartment - I bought one of those fancy chrome high amp alternators and after about a year it failed - it started drawing current when the motor was turned off. So I spent a few bucks and had it "rebuilt", well after a few more months and a few races - it spun a bearing or something, so it went back for another repair. OK, now with fresh repairs I trot up to West Palm Beach for the All Chevy Show and Corvette Shootout... of course I melted wires inside the alternator and now it's back in the shop. Mean while my "cheap-azz" $60 "back-up" alternator is back in the car - and the thing seems more realiable than the $300 chrome one. I should just have them switch out the guts and call it a day... I'll never learn, as soon as I get back the chrome one, it'll go back in, but maybe I'll drive with the spare hidden in the compartment behind the seat for awhile just in case.

OK, sorry for babbling - I'd take your alternator out and have it tested under a load - usually they will test it for free.

Just another thought... belt slipping? Worn? Check your belt tensioner!

Hope you get everything figured out, let us know what it was...

SilverBeast

I agree. It's probably not original but a replacement alternator. Have it tested, and you'll most like find that it's defective. It has nothing to do with the temp of your oil, but the alternator itself is giving you problems as it heats up. If you can, use rags and remove it and test it while it's hot. Don't buy a rebuilt alternator as it's a gamble. You may get a good one and you may not. Try for a new GM one, or, as someone suggested, buy one of the new single-wire units.

John Robinson

I agree just because it is rebuilt,new whatever don't assume it's ok. Remember what assume does it makes an a-- out of u and me. I too have had times when the replacement alternators were no good. One time I had to get 5 alternators in the same day to get one to work. Only after the parts house ran out of Chevy parts did I move up to Pontiac alt. and that was when I got a good one. Also replaced the coil one time and started a 500 mile trip only to find out the car would not run over 50. After several hours of searching and telling myself that the coil was brand new did I put the old one back in. Car ran fine and as far as I know the old coil is still in the car. Finally this year I found the cause of my lights dimming and going bright on my Olds. After 3 years of looking to fix this I found a service bulletin that discribed the problem of the lights dimming etc. Simply put there is a breaker in the alternator that under hot or cold conditions opens up and dumps the voltage to ground causing the car to run only on the battery when it does this. I got a new alternator with the upgrade parts in it and wonder of wonders no more light problems. By the way I had the old alternator tested a three differant places on the same day and they all said it tested perfect. Thats when I got out of my box and searced for service bulletins for my car. Just don't beleive everything the test equipment says sometimes you have to go with your gut instincts.

Bilyk

My car does the same thing

The voltage regulator is on it's way out

mitymek

flaky alternators.....very common thing.sometimes i think your best off to go to a junk yard and get one off a wreck.
if at all possible,get ahold of a KNOWN good working alternator off another vehicle and try it on yours before tearing into the wiring.
and make sure your idle rpms are up to spec.

silver84

check out this diagram,

http://misterbill.homeip.net/vette/w...%20circuit.jpg

what is the function of the middle wire {2}, to the regulator, I assume it is 'sense', but I don't know that.

rad, do you own a voltmeter?

radwebster

the alternator i got is a rebuilt from NAPA with a lifetime warranty. i already had to bring one back that was defective, so i guess i might as well do the same for this one. it idles at about 600 rpm's when warm.

thanks guys, i will replace it