voltage fluctuation
 

been having a problem with voltage in my car, at idle it fluctuates pretty bad, bounces around probably 4 volts or so at idle, but smooths out at speed. the done light and floor lights will actually fluctuate. Its now a larger problem/concern now that im using an electric fuel pump as opposed to my old mechanical setup.

I have a under drive pulley setup on the car.

So is this an issue of the alternation just not spinning fast enough at idle, or is the alternator just going bad already?

Phil,

Are you V-belt or serpentine?

v-belt

I had a underdrive pulley set up on my car and I had low voltage at idle. It didnt fluctuate much. It was still charging but just barley especially when the electric fans would kick in. I put the stock pulleys back on and sloved the problem.
I think you should put the stock pulleys back on and see what happens. I think your problem might be that the alt. might be on its way out and the underdrive pulleys are just making it worse.

I'd try the stock pulley first, but if you are interested I have a pair of new V-belt alternators sitting here. You can use one for testing.

i dont have the stock pulley setup anymore, its been gone for years.

The alternator is only a year and a half old, i know that doesnt mean anything.

Thanks for the offer Bill, i have another one laying around somewhere, i'll swap it in and see what happens, and if its still an issue maybe i'll borrow one of yours before i buy more parts...

yea, when the fan turns on, all hell breaks loose and you can hear the pump struggling.

double check your electrical connections, maybe with the engine bouncing around at idle, it causes a weak or break in a connection somewhere. just a thought. that or upgrade the wiring

most of the wiring is new, the cables are 2/0, charging post cable to the alt is #6, the pump is wired in #10, fan is wired in #12, Ground cable is 2/0 and chassis ground cable is #4.

Im leaning towards the underdrive kit. The voltage used to bounce around before, but its more of an issue now with the electric pump, i dont want to burn it up.

hmmm well might be worth it to see what the alternator is putting out. maybe have it bench tested to ensure it is/isn't the issue. i would lose the u-pulley like you said though

yea, come to think about it, my power steering seems to suck a bit with the car at idle and trying to turn the wheel. I think i need a larger crank pulley to speed things up a bit.
Maybe i'll ditch these v-belts and go to a serpentine setup

Is your car cammed?

My car pulls the same stunt at night when I have a lot on and come to a quick stop. RPMS dip and the alternator kicks out until the engine comes back up.

cammed? nah its a stock 305.....:nod:

i havent tried it at night yet, if i turn the headlights on all hell will probably break loose.

I have the idle set at 1100 right now to keep the voltage decent, normally its 900.

Must have needed a tune up when I saw it. I sounded like it was missing on 5 cylinders. That poor 305. :lol:

hmmmm, maybe THATS the problem:lol:

k...

i got a larger crank pulley, much better at idle. The voltage sits at about 14.4-14.6volts. When i turn on the fuel pump to full speed, the interior lights, headlights, foglights, cooling fan and radio, voltage drops to 12.5 at idle, and only goes back up to about 13.5 or so with some rpm.

Seems my alternator is weak as well and cant keep up, or not large enough? its a 140amp jegs house brand one, maybe upgrade to a nicer one later this year if it bothers me that much.

well, i was going through my recepit pile and found that my alternator is only a 100 amp unit. I could have sworn it was a 140. Thats most likely the problem rather than the pulley. I do have the larger pulley, but now my waterpump is overdriven and i think im having cavitation issues.

Im going to pickup a larger alternator and ditch this shiney new crank pulley:-x

would that work on a 350? if you dont need it i may lol

when ever i start up my car my voltage sometimes is low and when i hit the gas a little the volts go up but i hear a squeking noise for almost 1 or seconds... its a brand new alt, not sure what amps....my voltage also jumps up and down when i use the blinkers!

its a 1 wire gm alternator, powder coated black, and not that old. Its bolted to a smallblock, no reason it would bolt to any other small block

If you want it, it will bo for sale, lmk

v-belts or serpentine?

V -belt

i had the car running for about 10 minutes last week with the new alternator.
at idle the voltage is 12.5v, but steady. even with headlights, fuel pump, fans, dome light, ect on.
at least that problem is solved

did you stay with a 1-wire?

yes, actually the new alternator is a true 1 wire, there are no hookups for the field wires.

the older ones i had were called 1 wire alt's, but still have the field hookups

I like the new alternator, its a little smaller, and looks cooler