at like 4200-4600 my voltage drops from 13.9-14 solid to a 12.5-12.8 then when i shift it hops back up and does it again through 2nd and 3rd gear so its probably not belt slip.. its enough to make the headlights and dash lights flicker, imagine it wouldnt be good for the injectors at that rpm either i noticed this when i was going through my scanner runs... i got it tested and its fine, but i imagine they only test it for idle rpms.. does this sound like a regulator?? brushes? or some other alternator part?? its off a 92 350 tpi btw..

The first thing you need to do is verify the ECM output of the sensed voltage with a real voltmeter. The ECM may just be reporting wrong if the supply line to it cannot pass the ground current created by static injectors, causing the ground reference voltage to float up.

If the voltmeter agrees with the ECM, my WAG is that something is awry on the rotor. Either the slip rings are not concentric and are causing brush bounce, the brush springs are weak, or a rotor winding is loose and centrifugal force is separating the connection.

I can't imagine that the load of static injectors and a highly taxed ignition system would exceed the capacity of even the smallest alternator at those RPM ranges.

It is also possible that another part of the electrical system has a conection that will not pass adequate current, but you should be able simulate that with loads such as the headlights, HVAC blower, A/C, lighter, radio, etc. without having to operate at that RPM.

well the lights and gauge and computer are all in sync with the voltage drop... this is even at neutral i checked just reving it...

at idle I turn on everything electrical i can and it drops down to the same place so im gonna blame the alternator and get a new one sometime next year

the alternator is pretty much new, i took it apart to polish the outter halves and i musta messed it up

Just a tip since Vader covered the bases. I have actually had that happen to me. Reason is aftermarket brush/holder assy. Some of the aftermarket holders have more tolerance and allow the brushes more end play. This does 2 things, it results in uneven brush wear and at high rpm the brushes tend to bounce causing erratic contact with the commutator. I used a scope and looked at the field power line on the plug and noticed high level noise spikes. The brush holder in question came from a place that sells kits and the housing was already burnt at the end after only a year. A delco brush assy solved the problem.