Question1983 cadillac coupe deville, ht4100(4.1L 250 V8),89000+ miles.
All of the sudden my Service Now light came on. Did some checks and alternator was putting out about 11-12 volts.(Original alternator that came with the car) I replaced it, same problem 11-12 volt output. Thought maybe the battery was bad(1 yr old battery) so i bought another, same thing. Took it to Autozone, did load test on it with alt. in car, first time it said replace alternator(original). I replaced it, load tested it again and it said to check the alt. wires, wires were clean and tight. Replaced the alternator 2 more times, each time when i start it it reads 14.5 volts, I then turn the headlights and the defrost on(need those in the morning for work) and the voltage drops to about 11-12 volts. Today i replaced the connector that plugs into the alternator and it did just what i had said, 14.5 volts to 11-12 volts when i turned them on. Noone at autozone or anywhere ive called knows what would cause it. I have also done an ammeter test with the fuses. Nothing was pulling a drain other than the ECM. There is NO aftermarket audio system. The only thing that has been replaced is the transmission,(it sat for a long while before this happened but ran perfect when i got it)the alternator/connector, battery and the alternator belt. PLEASE HELP!!!
AnswerHi Paul,
If the alternator isn't putting out as it should be the first thing that needs to be checked is the battery because it really has an influence as to how the alternator charges. Since you have a new/good battery...hopefully the cables where they attach to the battery are corrosion free...and the alternator has been replaced several times and tested the problem shouldn't be with those 2 components.
The next place to look is the AIR pump belt because it drives the alternator belt. It has a tendency to loosen up and when it does the alternator doesn't turn as fast because of the belt slipping on the AIR pump pulley. To verify this with the engine off place your thumb on the fan blade of the alternator and try to push/turn it. It shouldn't move at all and if it moves easily then you have probably found your problem. There is 1 bolt in behind the AIR pump that you will need to access from below and loosen otherwise the pump will not move when you turn the tensioning bolt as well as 2 in front.
There is another possibility and that is that the idle speed is too slow to allow the alternator to charge properly with everything on. If you raise the idle speed up by pressing your foot on the accelerator and your voltage returns to the 14 volt range then try checking the adjustment of the minimum air/idle screw, throttle position sensor/TPS and the air gap for the idle speed control/ISC motor and maybe you can get the charging voltage to a normal range that way.
Try those suggestions and if you need more help let me know what happened and we can go from there. Bill
