I have a 2001 Blazer 4 door 4.3L 2WD and i think my alternator is bad. The things i have nticed are when i have the car at idle and i give it gas to about 3000RPM and let it go, the volts according to the gauge cluster go from 14.16 down to 13 volts and then it jumps back to 14.13-16 on idle. Another thing that i have noticed is i have a 1000watt RMS car audio systm and when i have my music up decently loud. My sub cuts out until i lower the volume a bit. The battery i have unde the hood is a brand new optima yellow top. The one with the light grey casing. I also have the big 3 upgrade using 1/0 tsunami oxygen free compotion power wire. My grounds on my amps are good. Full contact to metal. I sanded down the paint where i have them bolted to. What do you guys think i should do?? I belive the stock alternator is 100 amps. I was thinking to jumping to a 120 amp alternator or problobly even a 140 amp alternator. Input would be great. THNX

 

The dipping on sharp RPM decrease isn't too troubling actually. Given a set load on an alternator; at idle or low RPM, the PCM will regulate the alternator to supply for that demand. Now because the full field output of the alternator increases with increasing RPM, to output the same current as it did at a lower RPM, it will not have to work as hard so the PCM will again regulate the output for the demand. When you suddenly drop the engine RPM, the PCM plays catch up. It dials up the output from the alternator to meet the demand given the lower RPM. On some vehicles it may over shoot, then under shoot again before coming to a rather consistent steady state of 14-14.5V.

What does the voltage do right before your amp cuts out? Have you monitored the voltage with an actual multimeter (dash gauge isn't too accurate)?