alternator issue? car idle?

[newbe60]

the car is a 68 camaro with an ls2 and the battery reads about 12.85 before i start it up.. at idle before the electric fan kicks in it reads about 14.5.. then after the electric fan kicks in the meter keeps jumping with the sound of he idle from 12.5 to 14... the engine sounds like it has a load and the meter jumps back and forth every other second from 12.5 to 14.. any ideas on why it does this and what i can do

[newbe60]

anyone have any ideas? tests i could do?

[bbcc]

How quickly is the voltage cycling? Is the idle swinging with respect to the fan turning on and off or is it swinging while the fan is continuously running? Also, how many amps is the electric fan drawing? A big fan can cause enough of a volt draw to not only increase the physical load on the alternator, but also decrease the voltage going to your ignintion system. This could potentialy retard the timing, resulting in a lower idle rpm. Two tests I would recomend off the bat is seeing how much the fan draws on when it kicks in (inrush current) and sustained operation current draw. It's been a while, but if inrush current is more than 2 or 3 times the running current (someone please correct me if I'm incorrect) then I would rethink your wire gauge size, and look into trying another fan motor.

Also, it wouldn't hurt to check the timing while the car is doing this to see if it is retarding (disconnect vacume adance/lockout mech advance if possible).

If the idle and system voltage are swinging while the fan is steadily running, the problem most likely lies within the alternators voltage regulator.

I hope this helps you out.

Cheers,
Ryer