fiveironfrenzy

I've got an 86 IROC 305 TPI auto.
Two weeks ago I had to change out my alternator and battery. I'm thinking my alt went bad ruining my battery. They both tested bad. A couple of days ago I noticed that at night my volts started dropping while at idle and would jump back up to 13 or slighty over while diving. Now it's even doing it during the day while sitting at a light, no a/c or lights.
Any ideas?

Enkil

My car does that to, but it's just a faulty gauge or a problem somewhere in the wiring. But when the gauge is going all over the place the voltage really isn't.

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89 iroc-z 305 tbi
k&n filtercharger, open element air filter. nuffin' else

Guest

Yea, I'd check the wires and make sure the connections are clean and tight. Check the ground too.

SpeedCat86

I have the same year and engine you do, and I noticed the same thing. Make sure you have the 105-110 amp alternator, as the TPI engine needs a lot of juice to run all those sensors and such. Most cars can't make all the voltage they need at idle, and early TPI cars are worse than most. Also, if you have a more powerful stereo, or higher wattage lights, like I do, you may want to consider the 140 amp alternator, especially if you spend a lot of time in traffic or at red lights.
During the day, at speed (no lights or blowers, just radios) I get about 15 volts. Stopped at a light, in the rain, with wipers, lights and blowers, my instrument lights dim in time with my turn signals.
Like I said, if you have a mostly stock setup, it is an annoying, but not life threatening problem. If you have, or are going to, install extra light, amps, etc., get the bigger alternator (140)

Smeg

My volt gauge started reading low after I had battery problems. I think the problems have gone away now I have a new battery, but the gauge is still low. It reads about 10v when the ign is on, and 13 when running.

Looking at the haynes firebird manual page 10-23, it shows the instrument panel and in that diagram the voltmeter is connected to the fuse box and ground. On page 10-16 it shows the voltmeter connected to the fuse box and to the alternator. If its the first one, I would guess that there is a bad earth in the instrument cluster. If its the second I think that the regulators bad, assuming of course that the gauge isnt.

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Smeg
89 GTA 5.7 TPI

Mark A Shields

Make sure the alternator belt is completely tight. And our guages are known to be inaccurate.

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"Rice burners are like tampons...Every pu$$y has to have one"
'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat, just switched to 180* b/c of winter coming and going to college in the mts.
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite

Teddy Z

My car's voltage gauge fluctuated all summer until I cleaned my corroding battery connections and put some dielectric grease on them. Since then it's been solid.