Excessive electrical load/charging issue?

[73k5blazer]

I have this issue on my '89 Pontiac 6000 w/3.1L.

Not running, cold, 12.5v normal...start it up and it has 13.9v or so for a few mins. After a few mins, voltage drops to 12.5 or so and keeps falling slowly to around the 11.7 mark after 15mins or so. Worse, you can hear the load kinda kick in on the engine when it happens, like you just hooked up another dead battery for jumping or something.
If you rev the engine it comes up a bit, but no where near 14 where it should be. If you drive it it won't lose the battle most of the time, but won't be 14 either. COming to lights is nervous as sometimes it'll drop to 11 and the engine starts to get a bit rough probably because the voltage is dropping to a point where the fuel pump can't keep up. Yes, the problem seems worse at idle in gear but I think that's just because rpm is a bit less sitting in gear than in park. Also worse at night with the lights on.

I've checked positive cable connections, negative main cables and a few grounds elsewhere including engine ground strap. I also checked the main alt. feed cable and cleaned them all up.

I've changed the battery for a brand new one thinking mabey the battery had a dead cell. After that didn't change the behavior at all, I changed the alternator even though three different places tested the old one as just fine. Also, didn't help. I've tried jiggling various wire harness's, cables, near the starter, battery, alternator and many other places, no amount of jiggling changes the voltage.
Nothing seems to fix it. It doesn't appear anyone's messed with anything previous, there's no additional electrical accessories, no add on amps/stereos/lights/winches (it is an AWD car, mabey it needs a winch!)

There seems to be some kinda of load constantly somewhere but only if it's running and not dead cold.

I'm rather puzzled on this one and don't know where to look next. Any suggestions??

 

[rampage]

I was going to say maybe a rectifier died in the alternator, but you changed that. My next thought would be internal corrosion inside a battery cable. Way to check that is get a heavy gauge wire (like a jumper cable) and temporarily run it parallel to the alternator wire to see if that helps. Do the same for the wire going to the starter and any other heavy gauge wire coming off of the battery.

 

[diesel4me]

I'd also look for any fusible links that might be half fried or corroded inside..most GM cars have them,just like the older square body trucks..
They can allow current to flow normally when cold,but after a few minutes resistance builds up and chokes the flow of current when there isn't enough good strands of wire left inside..

I'd look at any circuit that is hot all the time,like headlamps and brake lights,for any shorted wires to ground too..

I've seen a starter solenoid eff up and cause a similar situation,without it affecting the starter operation,or making the starter try to turn on..

 

[Blue85]

Do you have an ammeter to clamp on? Would tell you if something is really drawing a ton or the alternator just isn't being commanded to charge. You can also start pulling fuses to see if the load drops.

Are you using a battery charger or how is it getting back to 12.5V before you start? I would look up the wiring for alternator control and see where the sense is connected, if there's a diode in there and if it uses the dash light in the circuit.

 

[73k5blazer]

mother puss buckets. You'll.never guess what it was


a bad mother f'ing battery. The one I bought from the store I noticed was a bit weak out of the box. I left it on a 1amp taper down charger overnight. Put it in the car and it starts it but you can tell still weak...well...i can tell now. Every time.you'd drive the car the voltage would drop away slow and the alternator would heat up like an SOB.
2nd night charger again...remove from charger 12.5v. But while starting would drop to 4. So I took it back.to the atore today and they tested it...yeah it says only good for 155cca. Supposed to be 720.

Optima red top junk. Only because interstate was 6 days to get the group 75 batt i needed. .

They pull a new one and test it...740cca. Awesome. I put it in the car and I could tell immediately as it whipped that starter at a speed I hadn't heard yet. Voltage at 11 or so while starting...normal. 14.1v steady at idle
I let it warm up...still 14.1 ...i turn on all lights , rear defrost, full fan, p/windows all.four at once and it drops.to 13.1 . In gear at idle with lights on warmed up....13.9.

so....what are the damn odds. Two bad batts in a row? It was perhaps a conglomeration initially of weak alternator with bad old battery with a few bad connection's somewhere. Who knows.

optima......i think it'll be my last one.

 

[diesel4me]

Maybe it was a "returned" battery someone else had issues with ?..

Some parts stores here will just hand over another battery if the customer has issues with a new one right away,to avoid pissing them off--then they just recharge and load test it,and put it back in stock if it tests OK--if they return again in a few days with the second battery dead,they will tell the customer the car had another problem (bad alternator,wiring,etc)--sometimes those "tested good" batteries end up being permanently wounded and do not hold a charge for long..

Most stores are honest and will sell those "slightly used but tests OK" batteries at a steep discount,but they also wont honor the full warranty,instead they give you like 30 or 90 days and after that--too bad,you own it..other stores just play dumb and sell the battery twice without telling you it was already bought once before..