89firebirdlb8

Hi i have a 91 firebird and im not sure whats wrong with my car. first of all when im at a stop and its in gear and the ac is on the volt meter sometimes drops down to 11-12 volts. i know alternators are suspose to run at around 13-14. i checked it with a volt meter so i know its not the gauge. i also just replaced it cause my old alternator started running at 8 or less volts at idle. im not sure if i got a bad alternator or if its just the heat for some reason. but when im on the highway it never drops below 12. also when im at a stop my tempature goes up to 220 wich i read is normal but if im stopped long enough without the ac on it will go higher. maybe my cooling fan relay?? and non of these things started till it got above 90 degrees outside. any help would be great i feel like im gonna get stuck somewhere from my alternator going out or over heating in traffic. thanks!

mauijerky

My car was acting similar as yours with the voltage. My alt is new, but noticed the 11-12 volts at idle with ac on. I just blamed it on being a crappy rebuilt alternator. Didn't worry too much about it because volts came back up once I got moving. Then, for other reasons I recently put in a new ignition switch. (the electrical part where the wires plug in) Its only been a couple days, but volts always stay around 13-14 now.

Assuming the new alternator is good, then somewhere in the wiring there might be a path of high resistance causing voltage drop. Look over all the wires and connections at the alternator. Make sure everything is clean and tight. Are all the wires still in good shape? Are all the engine ground straps still tight and in good shape?

As for your engine temp issues...do you know if the fan is coming on or not? Confirm that then go from there. Turning on the AC makes the fan stay on. If fan is on with ac but never when off, then fan switch is faulty or has become unplugged. TBI cars have the switch on the passenger cylinder head. I believe TPI cars are controlled by the ECM via coolant temp sensor.

Bob88GTA

iTrader: (2)

You gotta remember that when you are at a stop sign/light, at idle, with the air on, you are powering the AC unit, it's fan/fans, running all the accessories such as stereo/amp if you have that, PLUS you are illuminating the rear tail
lights. So, with that said, I think you fine.

tyeo098

^ This, and when the engine is at idle, its spinning at literally its slowest speed, so the alt is also spinning slow, which means less juice.

You could try going to your local yank-it-out and pull a heavy dooty alt from a C/K or Blazer.

Bob88GTA

iTrader: (2)

My 88 Has the GM 140 amp, digital dash and all that, and as I sit at a stop, mine does the same as he stated.

, sorta, Like you said tyeo098.... its spinning at its slowest so I don't think even a heavy duty would help.

I forgot to ask 89firebirdlb8...what are you even idling at with AC on? 650rpm in DRIVE, with AC OFF

Scorpner

iTrader: (4)

My 2.8 did the same thing. It seemed fine until you had the head lights and HVAC on. You could see the needle move when I turned the lights on and off. It went away after swapping out the alternator. Thing is too that with the weak voltage output, it affected how it ran so it would want to stall out when sitting at a stoplight. Kind of a down hill chain of events. lol

New ones these days doesn't always mean they're any good. I was talking to one manager that told me that they don't even change the bushings on the cheaper lifetime units. True or not, I had a lifetime warranty on one car that I had to swap 3-4 times until we finally got rid of the car. It wasn't an electrical issue either because it would work fine while gradually getting louder over time.
If you have a local rebuilder, have them rebuild your old alternator. That's my next step after the junk yard.

Also make sure that you don't have an under drive pulley. I'm not sure if they even make them for 2.8's. lol

bop11

11-12 volts at idle isn't bad, but the temp rise might be a clue. If your fan is going bad it will require a lot of power to run and not put enough air flow through the radiator. So the fan may be running slowly due to bad bearings or worn out motor. At idle the alternator is only capable of putting out a little power and a bad fan might be using a lot of it.

89firebirdlb8

Oh actually that was my first firebird lol this firebird is a 91 3.1l I believe it runs at about 650-800 toms at idle depending if it's in gear or the AC on. And I'll have to go let it run and see of the cooling fans ever come on without the AC. Does anyone know if there's a low speed and high speed to the fan or just one speed? And by the way thanks for the help!