98 Blazer charging system question

Wed October 03, 2012
1998 Blazer, with 4.3, LS package. Power this and that. 200k plus miles.
Been a bit humid last few days. I've noticed while idling, or sometimes
while going down the road, the volt meter will occasionally go dowm about 10 volts and then back up to 14.
Tonight, I bought some belt dressing, and spray on. Not much difference. Figured it might be the belt slipping, glazed.
Get home, the running voltage is about 14.15 volts, checked with my free HF meter. The battery came with the truck, unknown age. Water is low but over the plates. I don't have any distilled to put in. Get some, tomorrow.
What else should I check, for diagnostic? What to expect to find, and what might be the problem?
Christopher A. Young Learn more about Jesus www.lds.org .
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says...

Sounds to me like the alternator or voltage regulator/charging controller gizmo (whatever that might be), or cables/wires to those are cutting out.
And when that happens, the vehicle is running entirely off the battery, thus 10 volts. Then when the charging system works again, the voltage goes back up to 14 volts.
And if you have a fully charged battery, it will be around 12.75 volts. When you place an electrical load on it, the voltage will drop depending on the amount of the load and the condition of the battery.
I would check all main electrical connections associated with the alternator. Don't forget to check the large ground wires going to the body and engine. Be sure the connections are clean and tight. That the wires are not cut or damaged.
It is also possible there is a loose connection to the voltmeter on the dash or with a main electrical wire. You can confirm the voltage is in fact dropping by connecting a voltmeter to the battery. See that the voltmeter drops at the same time the dash voltmeter drops.
If all the above checks ok, I would then replace the alternator "just because" if it is old. Those do wear out due to the moving parts. So I would replace that for preventative maintenance if for no other reason. And replace the belt as well if it is worn. Again preventative maintenance - makes the vehicle less likely to break down out in the middle of nowhere!
And then if that does not resolve the issue, then I would learn more about other components in the charging system (voltage regulation) - check the wiring/connections to that and/or replace the voltage regulator.
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Sounds to me like the alternator or voltage regulator/charging controller gizmo (whatever that might be), or cables/wires to those are cutting out.
CY: Yes, those gizmos tend to whadaycallit.
And when that happens, the vehicle is running entirely off the battery, thus 10 volts. Then when the charging system works again, the voltage goes back up to 14 volts.
CY: Makes sense.
And if you have a fully charged battery, it will be around 12.75 volts. When you place an electrical load on it, the voltage will drop depending on the amount of the load and the condition of the battery.
CY: Ayuh.
I would check all main electrical connections associated with the alternator. Don't forget to check the large ground wires going to the body and engine. Be sure the connections are clean and tight. That the wires are not cut or damaged.
CY: Now it's daylight, I'll have to go take a look. I'm thinking to fill the battery, got to go buy some distilled water. Clean the terminals, while I have the lid up.
It is also possible there is a loose connection to the voltmeter on the dash or with a main electrical wire. You can confirm the voltage is in fact dropping by connecting a voltmeter to the battery. See that the voltmeter drops at the same time the dash voltmeter drops.
CY: Well, the lights dim.
If all the above checks ok, I would then replace the alternator "just because" if it is old. Those do wear out due to the moving parts. So I would replace that for preventative maintenance if for no other reason. And replace the belt as well if it is worn. Again preventative maintenance - makes the vehicle less likely to break down out in the middle of nowhere!
CY: My last Blazer, the alt was $130 or so, I'd replace that if I need to. I'm thinking battery first, as it's old and tired. And half the cost of alternator. Thanks for the very good ideas.
And then if that does not resolve the issue, then I would learn more about other components in the charging system (voltage regulation) - check the wiring/connections to that and/or replace the voltage regulator.
CY: I'm fairly sure the regulator is built into the $130 alternator.
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Stormin Mormon wrote:

Pull the battery cables and check the terminal to cable connection. They are known to get corroded under the rubber and cause things like this. Also look at the rear of the engine for a ground strap (attached to the back of the head between the heater plenum and the distributor). They have been known to get cruddy and cause voltage issues. Both will be made worse with moisture. Both are very common as well. The regulator is not usually a problem on these.
--
Steve W.

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You're very kind. I just pulled the clamps. VERY tiny bit of white corrosion on positive. My guess is the battery is done for. No way to know how old. Water in cells is low, I'm going to get some distilled, now, at the store.
The ground seems to be to the engine block, right under the alternator. I can't easily get to that. If the problem isn't found, I may have to either reach in some how, or pull the alternator to get at the ground.
Christopher A. Young Learn more about Jesus www.lds.org .

Pull the battery cables and check the terminal to cable connection. They are known to get corroded under the rubber and cause things like this. Also look at the rear of the engine for a ground strap (attached to the back of the head between the heater plenum and the distributor). They have been known to get cruddy and cause voltage issues. Both will be made worse with moisture. Both are very common as well. The regulator is not usually a problem on these.
--
Steve W.



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Stormin Mormon wrote:

The problem usually isn't between the battery and the connector, it's usually between the connector and the cable itself, under the molded rubber. Over the years the acid wicks down and destroys the connector. I've had a few fall off with just a slight tug.

That would be the battery to block ground. The one I'm talking about is a block to body strap, usually hidden on the back of the engine. They rot off and you get funky readings from gauges.

--
Steve W.

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CY: Just replaced the alternator, which helped a lot. Now I get 14 volts, unless I run the defrost and two windows at the same time, then it dips to 13 on the dash gage.

The problem usually isn't between the battery and the connector, it's usually between the connector and the cable itself, under the molded rubber. Over the years the acid wicks down and destroys the connector. I've had a few fall off with just a slight tug.
CY: These looked good. I havn't thought to look there. But, I'd have noticed.

That would be the battery to block ground. The one I'm talking about is a block to body strap, usually hidden on the back of the engine. They rot off and you get funky readings from gauges. CY: I did notice the negative cable went two directions. I didn't know to look there. Thanks for the teaching. Doesn't seem to be an issue, this time.
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*** snipped-for-privacy@hotmail.com says...

Sounds like you found and fixed the problem. The voltage should dip with a large electrical load. So that sounds about right.
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My thanks to the kind people on this list, without whom, I'd still be doing the deep dip and would be rapidly losing power.
Alternately, I could have been dead by now, not having the ability to charge.
But, I'm writing on the computer, safely at ohm. Meeting little resistance.
Christopher A. Young Learn more about Jesus www.lds.org .
Sounds like you found and fixed the problem. The voltage should dip with a large electrical load. So that sounds about right.
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Yes, I pulled the battery cables. Push the bolt out with channel locks, and pull the rubber. Clean that all up, amazingly clean. I've seen much worse. Still voltage fluctuation.
Just put in a replacement alternator, and then top off the battery with distilled water. Starts, runs, and shows good voltage. Only $85 for the discount rebuilt, I'd been fearing more like $150.
The ground strap didn't look too bad. Passenger side front, under the alternator. I didn't touch it.
Christopher A. Young Learn more about Jesus www.lds.org .
Pull the battery cables and check the terminal to cable connection. They are known to get corroded under the rubber and cause things like this. Also look at the rear of the engine for a ground strap (attached to the back of the head between the heater plenum and the distributor). They have been known to get cruddy and cause voltage issues. Both will be made worse with moisture. Both are very common as well. The regulator is not usually a problem on these.
--
Steve W.



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Last time we had a similar problem we had an intermittent ground between the engine block and the chassis. Easy to check with a volt meter between the block and the negative on the battery. Easier to test ... use one side of a jumper cable between the engine block and the chassis and or the negative terminal on the battery.
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