I have the weirdest charging problem ive ever seen. When my car is cold it charges great but as it gets warmer the volts start dropping. It starts when its cold at 13.5-14.0 volts but as it warms drop to 12.8-13.2. I have replaced the ignition switch, battery, and alternator. Why would it not charge only after it gets hot? I am checking my volts through a snap on scanner and my guage. Any help guys?

 

have you done a voltage drop test? from the alt to the battery, them form the the battery (neg) the engine ground. Need to make suer that aren't over a few tenths. if the reading is over .3 of a volt, may be loose connection, dirty, or the cable has high resistance and should be replaced. Are all of the grounding strips clean and tight?

 

The alternator charges based on demand. When you first start your car, you have just put the largest drain on the system that it will normally see. The voltage regulator in the alt will tell it to charge higher to try to replenish all that power you just used. The engine is also running a little faster when cold and output will usually be a little higher at higher rpms than low ones.

As the alt replenishes the power, the demand goes down and so does the charging rate. My alt charges about the same as you described yours when hot. It could be a little higher, but I have not had any problems. Your scenario sounds fairly normal.

 

Ive checked a few ground and really havent found any really bad spots, how bad would it be to do away with my underdrive crank pulley and leave the overdrive alt pully would it kill the alt really fast or could it handle it? When the lights are on at night the volts drop to as low as 12.2 and is really slow of starting. It sounds like the timing is set relly high on an old car. It really hurts the performance of the car when it starts to drop, as well the aggrivation of it wondering if its gonna start. Thaks guys im gonna try a few more things.

 

Why didn't you provide this important information in the first post? It changes the complexion of the issue. Sounds like the voltage regulator in the alt is not able to compensate. If you purchased a rebuilt one, it might not be so good. You might want to have it load tested. Do check all your connections, though.

 

The alt. came strait from GM. I paid like 190 bux for it. I thought i did mention it but i guess i didnt, Could the alt have went bad this quickly? It looks as if the wire that connects to the back of the alt. has been warm at one time or another due to the heat wrap being beveled. It jus seems like it would be a pain to replace the positive battery cable, but if thats what it takes. I think im gonna drive it to my local auto zone see what they think of the alt.