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Paging all Gm tech's or people really smart with GM electronics

1-tonmudder

1-tonmudder

1/2 ton status
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Apr 24, 2005
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In a junkyard somewhere
I have been working on my nephews 95 S-10 Blazer,When it came to me it had a bad trans and a busted heater core.I pulled the 4L60 and had it rebuilt,put it back in and drove it around for a day or so before tackling the heater core.

Since I put the heater core back in it will not keep a battery charged.I have had the alt tested and it tested good (14.5 volts) but it would'nt keep the battery up.Bein skeptical I put on a used one that also tested good(14.5 volts) and it was no better.It had a red top Optima on it that looked fairly new and I felt it was good but I was tryin to cover all the bases so I put a battery that I knew was good on and it did the same thing.With the engine running you can put a meter on the battery and watch it drop voltage as it runs.I undestand that it will do that since it's pullin voltage out of the battery and none is goin back in.It will run for 15-20 min before goin dead.The voltage on the alt post is/will be the same as the battery everytime.



Is there anything behind the dash that I could have missed that would keep the alt from charging???Seems awful coincedental that it happened after I had the dash apart.Any help is appreciated as he is coming Fri to get it.
 
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Hate to sound like a dick, but did you check all your fuses? Seems less like a draw, and more like the alt not charging.
 
Yeah I should have said that.:D I have checked them-several times.I went back out to see if it would start back.Turn the switch over and nothing,dash lights but wouldnt attempt to turn over,so I checked the voltage and the battery was 12.7 volts which I know is low but it should have turned it over.I put the Optima back on and it was 13.5 volts and it still won't do anything.I have had to peck on the starter before to get it to turn but I contributed that to a low battery.Could a bad starter be causing these problems???
 
Fuseable links in any of the positive cables? There should be one in the wire to the alternator.
 
Only way to tell is check continuity with a meter. Should have basically zero resistance.
 
Are the battery cables good? Could be that they are bad, even if they pass a continuity test, they still might not be able to support the full load of the starter or running engine.
 
When you put the dash back in, did you remember to reconnect the connector that tucks in behind the fuse panel area? It has like 4 or 5 heavy gauge wires going through it.
 
being a 95, it probably has a sidepost battery. I would make sure that the terminals are good. Sometimes the bolts will draw tight but not make a good connection, causing it to not start.
 
The voltage on the alt post is/will be the same as the battery everytime.
Click to expand...

shouldn't the alternator post that's connected to the battery be ~14v when the motor is running? It should at least be higher than the battery. If it's not, I'd check the voltage sensor wire continuity from the alternator to where it connects to a junction box (it'll be full battery voltage). That wire is supposed to let the voltage regulator know that the battery is draining and to increase the charge voltage.
 
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Can't speak from experience with the S10's, but on the TBI Blazers with a dash voltmeter, we have a resistor built into the wire that goes to the voltmeter. Vehicles with idiot lights do not have this resistor, but the wires are still there (bulb acts as a resistor). This wire uses electricity to create the magnetic field to operate the alternator. The resistance drops the voltage to the required range (~15 ohms, 1/2 watt IIRC).

Is your voltmeter / idiot light operating? If not, you might not be activating your field in your alternator.
 
Now that i reread, the fact that the truck runs, then doesn't even try to crank is going to be battery cables.

I jumped my truck, drove it 5 hrs home, and couldn't restart it in the driveway. The cables rot from teh inside out, if you hack the end off, you will see the corrosion. The easiest/cleanest replacement is the ones from teh dealer, but you can get by on kragen ones. Change both pos and negative cables, and you should be good to go.
 
I have been doin a lot of checkin,readin and head scratchin and have found that the single brown wire that connects to the regulator doesnt have any juice on it at all.Shouldnt that have power with the key on???? Goin back to what Randy said it has a gauge but it doesnt work,it didnt when it came here,so if thats supposed to make a circuit that could be why I dont have voltage goin into the reg,correct?????
 
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