3G Alt Output At Idle Question


Founding Member
Jul 18, 2002
Big Stone Gap, VA
I have a PA Performance 3G upgrade on my car, using their wiring kit as well. My car still acts about like a stock alt when you have the lights/radio on etc. At idle the lights will dim and when you rev it up, they will get brighter. This annoys me to no end and I want to fix it. How much output should one have at idle? I do have a underdrive crank pulley on the car(will be changing out to stock crank pulley when A/C goes back on the car). Is that crank pulley causing the alt to turn that much slower that its causing this to happen? The PA Performance 3G alts are "supposed" to put out more power than the stock alts as well based on their website. How much volts should I be seeing at idle and where is the best place to measure it at? Thanks!
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Dave, this is one of those things where just a slight bump in idle speed (or changing of pulleys) can really change things. For instance, with the 160 amp alt I have in the 94 (80 amps at idle), my commanded idle was raised ~175 RPM or so to get the output where I was happy. I could have overdriven the alt as well (stock pulleys on the car otherwise).

If goosing the throttle just a hair helps things out, overdriving the alt should help if putting the stock crank pulley on doesnt.

As far as voltage, 12.66 volts is break-even. Measure it at the battery. Or you can measure battery voltage and then voltage somewhere inside the car. Note the voltage drop and then leave the meter connected inside the car. Add the voltage-drop spec to the meter reading to guestimate what the battery is reading as you drive. Ideally you'd never drop below about 13.2 volts at any time.

Good luck bud.
Measured it at the battery today, at idle with just the radio on it was between 12.8-13.3, with the headlights/foglights, radio and electric fan on it was around the 11.3 range.

Def pulling some power, the car idles around the 700-800rpm range I would guess.
I see whatcha mean. Just about any lower and you'll have the battery light start flickering. I smell a crank and alt pulley swap coming, esp since your idle is relatively high already.

The last possibility to consider is that the alt dropped a diode. However, if volts jump back up to 13.0+ with a full load at 2000 RPM, this isn't likely. If your output never gets very high with a full load, have the alt bench tested.

Good luck Dave.
my 3g with UD pullies puts out right around 13 at idle (~700rpm), but thats just reading off the stock gauge (which actually seems fairly accurate compared to the rest of the gauges). lights, stereo, and heater fan on, it drops to around 12, but the lights never dim at all. i do have a top of the line battery, which may be why i don't see the issues you're having... might be another thing to check into...
Thanks guys.

Yeah if it gets some rpm going then the volts jump up like they should be. I'm planning on throwing the stock crank pulley and 93 Cobra waterpump pulley on it, I don't have the complete set of underdrives, just have the crank pulley.

Is the alt pulley in those kits smaller than a stock pulley? If so, maybe I need to go with a stock crank, 93 Cobra wp and a overdrive alt pulley to get it where I want it.
sounds to me like you may have something else going on because i have the 130 amp alt and underdrives and my car is over 14 amps...although i do have my idle closer to 900...you may want to try and up the idle as others have mentioned if you dont want to remove the under drive pulleys...