Charging system WEIRDNESS, need advice

[mtnmankev]

84 K-10 with 350.
For a couple years I have had an issue with what appeared to be a weak alternator, so today I grabbed a spare from the shelf, installed a rebuild kit, and swapped them in the truck.
At idle I get about 10.5 volts, NOTHING but the engine running to use any power.
Rev the engine and volts climb to 13.
Let gas pedal go back to an idle and volts drop to about 10.5 again.
What should I be looking for to find the problem ?

 

[bucket]

I'm curious where you got the rebuild kit? The only place I knew that you could still get alternator rebuild kits was Fleet Farm. But they recently discontinued stocking those kits.

 

[mtnmankev]

I'm curious where you got the rebuild kit? The only place I knew that you could still get alternator rebuild kits was Fleet Farm. But they recently discontinued stocking those kits.

Bought on ebay, 26 bucks and change, free shipping.
Complete kit.

 

[SirRobyn0]

If you are sure that your rebuild is solid I'd be looking for a high resistance wire. I once had a mid-90's Grand Cherokee in at the shop doing pretty much what you are describing. Part of the main charge wire insulation had broken down, moisture got in and the wire corroded creating high resistance. The alternator could only over come this when the engine was reved up. Other than that check grounds, and battery terminal and associated connections. Not sure how much this all helps but it's what I have.

 

[mtnmankev]

If you are sure that your rebuild is solid I'd be looking for a high resistance wire. I once had a mid-90's Grand Cherokee in at the shop doing pretty much what you are describing. Part of the main charge wire insulation had broken down, moisture got in and the wire corroded creating high resistance. The alternator could only over come this when the engine was reved up. Other than that check grounds, and battery terminal and associated connections. Not sure how much this all helps but it's what I have.

Thanks, I will get the alternator tested to make sure the rebuild went well, but the truck did the same thing with the old alternator.
How do I test the wires for high resistance ?
If the problem doesn't get figured out, the truck is no good to me and is going away, might save the 383 stroker for my other truck and scrap the rest of the K-10.
Shame to see a no rust truck go bye-bye, but it happens, and it would save me on plates and insurance costs every year.

 

[ReefkoiC10]

What about pulley size? Since it gets better when the RPM is higher?

 

[bucket]

Is it possible that the belt is slipping?

 

[mtnmankev]

Is it possible that the belt is slipping?

I don't think so, I'm sure it would make some kind of squealing noise if it was slipping.
I can grab the alternator fan, spin it and it moves the cooling fan pulley on the water pump, but it isn't easy to make it spin.
I will try tightening the belt some more in the morning, but not gonna hold my breath that it'll be fixed.

 

[SirRobyn0]

Thanks, I will get the alternator tested to make sure the rebuild went well, but the truck did the same thing with the old alternator.
If the problem doesn't get figured out, the truck is no good to me and is going away, might save the 383 stroker for my other truck and scrap the rest of the K-10.
Shame to see a no rust truck go bye-bye, but it happens, and it would save me on plates and insurance costs every year.

As you know the charging circuit is relatively simple on these trucks. I mean you could run any large gauge wire off the back of the alternator to the battery as a test wire. Fire it up and see if it still does it.

I'm just curious is this the same truck you were having trouble with the control arm bushings a while back?

 

[mtnmankev]

As you know the charging circuit is relatively simple on these trucks. I mean you could run any large gauge wire off the back of the alternator to the battery as a test wire. Fire it up and see if it still does it.

I'm just curious is this the same truck you were having trouble with the control arm bushings a while back?

Nope, this is my 4x4 I use only as an emergency backup when we get a storm here and the roads get muddy and I absolutely HAVE to be able to get out.
For me to use the 4x4 truck on dry roads, somebody had better be dying or their house on fire.
The truck with the control arms issue is a two wheel drive, and it HATES any mud at all, and six miles to pavement (or driving back in) is impossible in that truck in muddy conditions.

 

[bucket]

I don't think so, I'm sure it would make some kind of squealing noise if it was slipping.
I can grab the alternator fan, spin it and it moves the cooling fan pulley on the water pump, but it isn't easy to make it spin.
I will try tightening the belt some more in the morning, but not gonna hold my breath that it'll be fixed.

Sounds like it's tight enough. A little deflection in the belt is good, too tight isn't good for the belt or the alternator either.

 

[SquareRoot]

Your exciter wire isn't exciting. This is why one wire alternators suck btw.

 

[mtnmankev]

Your exciter wire isn't exciting. This is why one wire alternators suck btw.

Try again ........
I have battery voltage at the red wire in the two prong connector, key off.
I have battery voltage at the small black wire when key is on.
I ran a heavy wire from the battery positive post to the alternator battery terminal, NO CHANGE, the truck still has the issue.
And no, the belt isn't slipping.
What's weird is, engine running, revved to get 13 volts on the meter, then let the truck idle.
Voltage drops around a half a volt and stays there for about 15 - 20 seconds, then it drops way down.

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[SirRobyn0]

Try again ........
I have battery voltage at the red wire in the two prong connector, key off.
I have battery voltage at the small black wire when key is on.
I ran a heavy wire from the battery positive post to the alternator battery terminal, NO CHANGE, the truck still has the issue.
And no, the belt isn't slipping.
What's weird is, engine running, revved to get 13 volts on the meter, then let the truck idle.
Voltage drops around a half a volt and stays there for about 15 - 20 seconds, then it drops way down.

Gee Kevin, kind of looking like an alternator problem. I'm sure you would have noticed this but I'm going to say it anyway, the truck isn't idling to slow by chance? I know your not very close to town, would it be easier to swap the known good alternator out of your other truck as a test unit?

 

[mtnmankev]

Gee Kevin, kind of looking like an alternator problem. I'm sure you would have noticed this but I'm going to say it anyway, the truck isn't idling to slow by chance? I know your not very close to town, would it be easier to swap the known good alternator out of your other truck as a test unit?

That is a good test, if it wasn't so hot outside and if I had the energy to do it.
Truck isn't idling too slow but good thought anyway.
It's possible the rebuild kit i bought has at least one defective part, and if that's the case I will see about a refund from the seller.
MAYBE O'Reilly's alternator tester machine can show up any problems.