I have a 97 Chevy Blazer 4x4 with a little over 113K miles. I've been
having problems with the voltage for a while now. The voltage gauge
swings from 14v to about 10.5v when I stop at a traffic light or a stop
sign. I'm convinced the gauge is not to blame because when I put a load
on it, it indicates 10 to 10.5v, the Dash lights dim, the headlights
will also dim. I've already replaced (3) alternators on this Truck (2)
batteries within (4) months and everything is still the same. The gauge
will read just above 14v and sometimes even 16.2v while am driving the
truck with no problem but the minute I stop at a traffic light the
Voltage Gauge drops down to 10v or 10.5v depending on what accessories
am runnning on my truck. The truck starts up good and the Voltage reads
a perfect 16.2v but the minute the truck is warmed up the Voltage then
starts to drop to about 11.5v then to 10.5v and then to10v Depending on
what accessories is running on the Truck. Temperature and frequency
between trips seems to not make a difference either. The only thing I
have done to the truck even remotely connected to the electrical system
is to swap the radio, but I used a wire harness to connect the wiring.
I've already checked for loose wires or bad grounds and their is none.
I've even had a addtional grounding wires installed but that did not
help either. Other than I'm lost. Any help?
I think it might help to quote the original msg. in your reply...
so that others in the group could see the question and the reply
and provide additional information if needed.
you can configure your newsreader to do this automatically.
I just went through this on my '95 Monte. Mine turned out to be bad
connections at the power distribution block.
First thing I did was test to see if the low voltage was system wide. I did
this by checking the voltage at every fuse and isolating which ones were at
the low voltage. Only a few were at the lower voltage and others were
normal. The voltage at the battery was also normal. This lead me back to the
power distribution block beside the battery. I took it all apart, cleaned it
up and all is like new.
Here's a link to the thread:
Try checking the voltage right at the battery. With the engine at a fast
idle and no accessories, then at a fast idle with headlamps on and the
heater blower on high. If you need a meter, Harbor Freight has them for
around $4.00 on sale. There are more tests to make but start with these. One
seemingly obvious thing a lot of folks miss is the belt. It has to be tight.
Before changing another battery or alternator:
Clean the terminals.
Check the pig tail from the distributor for damage or a lose wire in the
Get 'em warmed up, and take a trip to a autoparts store that has a
battery & alternator in vehicle load tester. Have it checked. Have them
run the test a few times try different accessiories.
I had a similar problem on my 95 5.7 K1500 trailer towing package several
weeks ago.....was getting low voltage and had a leaking battery terminal.
Replaced the battery and the starter went out the next day, don't think it
was related as I just replaced it 6 wks before (200,950 miles on the
original starter!), just a bad rebuilt starter. Anyway, replaced the
positive battery cable that goes from the battery to the drivers side
firewall distribution box as it was corroded from the inside from where the
battery had been leaking into it. The trailer towing package has two
positive leads that go to the positive side of the battery. One goes to the
starter and the other goes to the firewall distribution box. Cleaned all
connections and still had the fluxuating voltage. Would crank right up first
in the morning then later wouldn't crank at all, would just click. Would
tighten up the battery terminal, and would work fine for a little while and
start the whole process over. After overtighting the terminals on two
batteries and causing the positive side side mounts to come out we found out
what the problem was. The lead spacer that goes between the positive side
cables to the positive side post of the battery had been squashed down to
less than a 1/4 inch over the years. I put in a new spacer, it is like a
half inch or more in thickness and now that has fixed all of my electrical
problems. What was happening with the old spacer was that when I tightened
down the terminal on the positive side the long battery bolt would go thru
the side mount bung and poke a hole thru the battery. Thank goodness for
O'Reilly's liberal battery return policy, as it took two batteries to
discover what the problem was. Now both the terminals are good and tight and
I get a solid 14 volts in the middle of the voltmeter all the time now. This
is a little long winded but hopes it might help someone out there......Mark
This is normal. Believe it or not.
The alternators are set not to deliver full power at idle so they will not fail
in hot weather.
One way around this is to get a smaller alterantor pulley. Since you changed the
alternator, you may have gotten a larger pulley by
You can calculate the rpm needed, then using the diameters find a smaller pulley
that will help.
Dont go too small, as the alternator may then fail because it will be subject to
higher rpms are higher engin speeds (4500 rpm). I
believe 8000-9000 rpm is the upper limit.
Another approach is to replace the alternator with a larger unit, such as those
used on police and fire vehicles.
And if your savy, you can experiment with different mfgs' voltage regulators,
this worked for me.
fail in hot weather.
An alternator outputting 10.5V at idle is NOT normal. At idle, an alternator
will put out anywhere between 13.0V and 14.5V depending on load. If the
battery is at a low charge, you can expect to see around 14.5V. If the
battery does not require any charging and there is no big load (ie high
beams, rear defogger, large stereo), expect to see 13.5V or so.
What is the source of your information?
as you say above the alternator has to put out over 12.v at idle to
charge the battery. At idle once again you should see around 13.v if
the alternator is working properly.
I believe the amp output changes with rpm and load.
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Although, this is GM's response to the problem:
But not mine. When my vehicle started to exhibit these symptoms I fixed it.
My mom's Intrigue started doing it and the dealer wouldn't do anything other
than respond with "it's normal." She didn't care anyways, got rid of the
Regardless, if it didn't do it when it rolled off the assembly line, it's
not normal and it can be fixed.
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