I'm having stalling problems occasionaly, only when stopped, if I put it in neutral the RPMs stay around 700rpm. When I'm in drive it goes from 500-700 and sometimes stalls. I was sitting at a light and noticed that my car idling around 500rpm with lights and brakes on was about 12-12.5V. Is that right? I have a good alternator from my 89 V6 if they are the same.

 

When I had my stock alt. with all the elctrical stuff going, at an idle it'd show 12-13 volts on the gauge, with dim lights and all. Pull away or start driving gauge went up. So yours does'nt sound abnormal to me.

FWIW, I installed a 120amp alt last year in factory wired form, gauge always shoped 13.5 volts when all my electrical system was running, electricl water/fuel pumps dual ele fans, stereo, etc...took and installed 4 ga. wire from bat connection on back of alt to battery (mounted in rear) and now it shows 14volts at an idle/stoplight and 15-16 volts going down the road. Did output check and it's cranking out 14.78V so I'm happy with the upgrade to the bigger wire, fuel pump sounds ALOT better now

 

12.5V is closer to battery voltage, a good alternator with no loads or minimal loads will still put out a good 14Vs. most shops have equipment that can do alternator output tests and if its a stock alternator than can compare it to manufacturer's specs and tell you if its good/bad.

 

Thanks. Would a stock alternator from an 89 V6 firebird work? I haven't compared them but I think they are the same. I wouldn't mind just swapping it over and testing it out.

 

err, not sure. usually smaller engines don't need as much amps to run ingition and stuff like that but i couldn't see it drastically affecting it. i wouldn't just go about replacing it without making sure its faulty first, don't be a parts-uzi

 

I guess I wasn't sure of how the alternator test works, I thought you had to pull it for it.

 

The engine has NOTHING to do with what amp alternator you need. It depends on accessories, how many you've got and what kinda juice they draw. Why do you think a base model car only gets a 65amp alt., why a fully loaded with pwr everything gets 105-120amp?

Just start the car and put a digital voltmeter on the output of the alt to see what's it's cranking out for juice.

 

umm, according to what they taught us in school the output of the alternator in general will equal the cubic inches of the engine. but i'm not here to argue, you can take that up with the people who wrote wyotech's lectures.

when testing the alternator make sure you put a load on the engine such as turning on the headlights and rev the engine to about 2000-2500 rpm. its called the max output test. if you take amperage with the engine at idle then its just gonna give you like 20 amps or something small but when doing the max output you should get something around 150 if not higher than that since the engine its made for is bigger so i wouldn't be surprised if it was 200+. the explorer V6 in the our shop had a max output of 220 amps.

 

So what your saying is by taking an alternator off a V6 car turning 3000 rpm, it'll put out more amperage/voltage if your took that same alternator and installed it on a 632 mountain motor turning 3000?

Guess I never knew an alternator had a brain to know how many cubic inches it sat in front of, thought it was all internal with the regulator and windings on how much the alternator put out along with rpm since many alternators wont put out as much charge at an idle as they will at higher revolutions. Hence dim lights at a stoplight and then they brighten up when pulling away.

a......sure

 

I agree with IHI, engine displacement is completely irrelavant when it comes to the current the alternator can supply.

 

I'm not argueing with you, and am happy you could go to Wyotech. But sometimes a person is fed soo much information they look for answers alot deeper than they actually are.

I have a good friend that's been in plant maintenance for 20 yrs, has to get certified annually for certain things and is very smart on the technical side of things. He's so smart he called me over on day to trace down why his bathroom light quite working, told me he had juice at the switch, gave exact voltage coming from panel, etc...went over and changed his light bulb for him and walked away with a smile.

I may be wrong, guess my 65 amp alternator that could'nt keep up with my electrical load in the car since EVERYTHING is electric, musta been the flunky of his class since he did'nt know I installed him in front of my new 388-previously resided in front of my 355. Same thiing though, was getting pushed to the limits and could'nt keep up with demand. So I got a 120amp, HE musta knew what was behind him becasue he keeps everything charged with no dimming, actually 1 full volt higher under load than the previous alt.

 

you obviously misunderstood me, different size engines come with different rated alternators from the factory. and with different options and such the car would get a different and higher rated alternator as well. i KNOW what i'm talking about so please don't try to insult me, thankyou.

 

Read above and tell me how anybody coming across this was supposed to interpurt what you said.

That's what I was trying to get across. But based off your earlier post, it's easy to see what mislead me and probably everybody else that read it. I guess thinking outside the box I understand where your coming from since larger engines were options and usually when people bought cars they wanted all the options-go fast with creature comfort-so generalizing the statement larger cubic inch need larger alternators, when in fact it has nothing at all to do with the engine what-so-ever, just options

 

i apologize for being vague its just that i can only go by what i was taught, and that was that bigger engines have bigger alternators, but it usually only varies from 10-40 amps at most. nothing outrageous.