Pat Hall

iTrader: (31)

Hey everyone. I'm just wondering what the common voltage output should be for a stock 105 amp alternator when the motor's running. I hooked a multimeter up to the output wire on mine, and with the motor running I'm getting 14.3 volts. Is that adequate or is that too low? I revved the motor up and it stays at a consistent 14.3 volts. Also, when the cooling fan kicks on or if I turn on the headlights, the voltage drops for just a sec and then recovers back to 14.3 again pretty quick. The problem I've been having is my battery becomes discharged after the car sits for a few days. I tried hooking up a test light between the negative terminal of the battery and a ground point, and the light doesn't come on at all, so if something is draining the battery while the car sits, I'm not getting any indication with a test light. Any ideas guys? Oh yeah, one more thing, even though my multimeter reads 14.3 volts, the gauge in the dash only reads about 11 or 12 volts. Is this the gauge being inaccurate or is there possibly some sort of voltage drop between the output terminal on the alternator and the reading the dash gauge gets? Any help would be appreciated. I hate electrical issues! Btw, I have the body ground upgrade kit from Racetronix that they sell with their fuel pump kits. I'm gonna install that sometime this week and see if that helps anything.

jeff_blake

iTrader: (1)

most "normal" voltage is usually in the 13.8-15 range.

TreeFiddy

^^^

14.3V is about perfect. It's charging fine. Dropping upon application of a load and quickly recovering is the normal action of the regulator. Also fine.

The batt neg terminal and any ground point should be at exactly the same potential, ie no reading on voltmeter or test light. Still fine.

You have some kind of parasitic load flattening the battery while the car is off. Something little like interior light on, radio on, something like that. Pull off one of the batt terminals, and put an ammeter in series between the batt post and cable. Shouldn't be more than a few milliamps at rest.

Dash voltmeter is pretty inaccurate - does it at least show a reading that goes up a little when the engine is started?

Pat Hall

iTrader: (31)

Cool, yeah I figured 14.3 was probably in the OK range, just wasn't 100% sure. Yeah the volt gauge does go up some after engine is started. Sometimes it actually goes up to 13-14 volts, but then at other times it only seems to read around 8-9 volts. I've got probably about 4 extra volt gauges in other gauge clusters I've picked up in the yards, so it'd be easy enough to throw another one in the gauge cluster. I'm positive nothing stupid such as a small light or anything else is being left on. However I was thinking if I hook up my multimeter between the positive cable and positive battery terminal, maybe I could use the same idea as when it's hooked to the negative side and start pulling fuses one at a time and see if the draw, if there is any draw showing on the meter, drops when any of the fuses are pulled. I do have an aftermarket stereo deck in the car that's hooked straight to the battery terminal on the fuse block, but if it's working properly, the only draw it should be taking is the small amount used to maintain the memory. I always make sure the stereo is off and also the clock. Maybe something is messed up with the stereo and it's pulling too much. This car has always seemed to drain a battery somewhat. I originally had a L03 TBI engine in it, and with that setup it'd run the battery down if it sat for about 3 weeks. I've changed it over to a 350 TPI setup with the TPI harness, 165 ecm, etc., and since then it seems to drain it within a week or so, especially when the weather's cold. I think my best bet is to hook up the multimeter on the positive side and see what kind of reading, or draw it reads. I know the basics when it comes to electrical stuff, but I've never been too good at knowing how to diagnose these types of issues! So thanks again for the tips on how to chase down the problem!