Skysarge

Vehicle is 1981 G10, 6cyl.

A couple of times recently I have noticed at low speeds my alt light comes on, but goes off as soon as I pick up any speed.
About a month ago, I got ready to go when the engine started to tun over, then there was not enough elec power to turn it over. I wasn't sure if I left lights on or what.
I jumped it, drove home, stuck it on my charger. It started charging the battery at 6 amps for an hour or so, the slowly down to a little more than 3 amps.
Last week, it did the same thing, this time I knew I did not leave lights on.
Jumped it, stopped at auto parts store got battery checked. It passed.
Today, I did some running around locally. At my last stop I had to have it jumped again. I had been there 15 30 minutes. Got home, stuck on charger, rate was only 2 amps.
Anyone w/ideas as wassup?
Thanks -
Skysarge

kevinkpk

Unless you can test the alternator, with what you described it is in my opinion battery.

Skysarge

I will get the alternator tested.
But, I am curious why the battery tested OK, if it is indeed problematic.
Skysarge

kevinkpk

You can test the alternator with a voltmeter to check if it is charging. The battery could have a bad cell, you need to check each cell with a hydrometer, that looks like an anti-freeze tester, it checks the specific gravity of the acid/water in the cell.

SWHouston

I have a very inexpensive ($15) Digital "VOM", Volt/Ohm/Milliamp Meter from RShack. VERY handy ! Usually Alternator's output about 14.5 volts direct current, and the Battery needs at least 12 vdc to get the engine going.

Works great in the house as well, can check if a Lamp is burned out and voltage of A/C outlets, continuity of grounding, LOTS of stuff

No DIY'er should be without one !

Skysarge

Guess late follow-up better than no follow-up.
We stuck a meter on the battery, got 12.3 v with engine running.
Replaced alternator and belt 14V reading to battery. Belts were in poor shape which probably contributed to problem.
Noticed after replacing alternator. engine did not sound as noisy.

Next up - tune up w/plugs,points. etc. Getting occasional hard starts, requires holding gas pedal down fully and crank. Might be auto choke. When engine does fire, no mosquitoes in range survive.
Need to look at that problem.

Was thinking about changing automatic transmission fluid, clean filter, It shifts smoothly and no problems, no idea when it was last serviced. Check of fluid showed nothing unusual.
One suggestion from local wrench, "Leave it alone."

Thanks all who helped.

Skysarge

Skysarge

I had a nagging doubt in my military mind that replacing the alternator and belts was too simple a solution.
After putting on alternator, stuck unit on 6 amp charge that drifted to 2 amps fairly quickly, but wanted to insure battery was charged up, left in on for about three hours.
Drove to work this AM, headlights on. When time to leave work, cranked right over.
Ran around a bit, parked for a few hours, went to grocery. 30 minutes in grocery, would not fire up, acted like it was flooding or choke sticking. Had to hold pedal to floor while cranking. Cranked for about five or so seconds, battery would not hold to turn engine, just solenoid clicks. Jumped off another truck, took a few turns to crank, the fired up. Ran rough for a few seconds, smoothed out. Got home, about 20 minute drive, put back on charger, taking about 3 amps
Had battery tested about two weeks ago at auto parts store, read out was OK. Checked alternator when we put it on yesterday, it showed 14v to battery steady.
I am bumfuzzled, as in now what?

Skysarge

RacerX

IN 1981 the alternators had an external voltage regulator.

In the 90s everyone put the VR INSIDE the alternator.

Replace your voltage regulator and check belt tension. And replace your battery cables. They may be corroded inside the insulation where you cannot see.

kevinkpk

Ok as racerx says 81 has an external regulator, probably so. Is there a "small" black electrical box on the drivers side firewall with a 3 or 4 pin electrical connector? If so, it has an external. It is new enough to be electronic, and not the old point/relay type. These things are cheap, but since you read 14 volts with it running, and the battery is only taking 3 amps, I'd suspect loose belt (since it has trouble cranking at times). Also could be the VR intermittent. What the VR does is controls voltage to the field of the alternator to maintain a setpoint output of 14-14.5 volts or nominal. Now with the smoke, is it black? If so, and you suspect electric choke, I'd disconnect the wire to it, and with a pencil or stick whatever open the choke plate and try starting it with the pencil holding the choke plate open.

Now BACK (final) to the assumed battery issue not cranking, I don't think it is the battery, I think more than likley the elctrical charging problem is solved, but I think you are now having a starter solenoid problem. Have you had the starter off or replaced in recent times? Solenoids on GM's get hot, and the contact disc/contact will burn causing a bad connection with alot of current draw.

Skysarge

Follow up again with some answers to your questions and comments......
Alternator does have a VR built into it. Mechanic at my employer said to tell parts shop I wanted one that way, or if not available to get it separately. Counter man showed me the connector on the unit.
The battery cables are pretty new. PO got the van from our school district, put in a battery and cables and a few other things, about two years ago. Van wound up sitting around for some months, and being a storage trailer. I got it from him. As cheap as the cables are, I'll probably just replace them anyway.
The bad solenoid thought is next on my look-see list. When the parts store tested the alternator, he mentioned he could not get a proper reading as something was drawing off power. We thought it to be the alternator. But, if a bad solenoid can indeed siphon off, then that could just be the problem there. Added the the idea it is the starter solenoid kicking out, and not the battery losing charge, that seems to fit well as the cause.
Stay tuned for the next chapter.
And, many thanks to all who chipped in on this. You're saving me a lot of time and frustration, the former of which I have little, and the latter tons of it.

Skysarge