charging problems

[argve]

Ok my truck has refused to keep the batteries charged - so I stabbed the batteries while it was running and I get 11.5 volts.

Swapped out the alt to the tune of 130 clams to no gain. Still no charge batteries.

Can change batteries with battery charger and they take the charge and hold it.

Disconnected the grid heaters thinking that maybe they were pulling the system down - nope.

Connections on batteries and alt at pretty good - the connections on the alt I guess could be better but I've seen a ton worse in my life and they were working just fine - these just look normal.

Is there something that tells the alt to start charging.

My check engine light is on and it reports a shorted field in the alt as the code.

I'm getting tired of charging the batteries every night to make sure that I can drive it the next day.

I have never had this type of problem before but will say that I ran into this exact same problem on a neighbors 87 F150 just this week - no output from brand new alts... is there something in the cosmos that is doinking with alts in the Fort Wayne area that I should know about???????

 

[tonkadoctor]

Should be putting out 13 - 14 volts.

Take the truck in and get the charging system tested, including the batteries.

Bad diode in the alt will cause the alternator to drain the batteries overnight.

Voltage regulator tells it when to charge the batts and what voltage.

Shorted cell in one battery will drain both.



P.S. worked at Pep Boys for a few months, can tell you that just because it's new it doesn't mean squat. My personal record is swapping 4 different NEW REMAN alternators on the same chebby cavalier in a day. Nothing wrong with the batteries or rest of the car, just my s--t luck to pull 3 bad remans from the shelf in a row. Real QC work at the reman place there.

 

[Whit]

My guess would be a bad voltage regulator

should be charging 13.8volts

 

[argve]

I found it - 120 amp fuse was popped - output from alt is fused - fuse box is located on the drivers side fender - big square fuse.... Replaced that and it works great... me thinks that when I was replacing the alt and did NOT unhook the batteries and bumped the charge line against the engine and caused a huge spark that I took the fuse out then....

I didn't realize that it even had a fuse but this weekend when I got to playing with it again we noticed that the back of the alt was outputting 29 volts but the batteries were sitting at 11.5 that told me there was an open in the circuit so it was just a matter of following the wire...

Oh and I figured out that the voltage regulator is in the PCM and it's 400 clams for a replacement.