it sounds like the internal regulator to me... what brand is it?

 

If it was refurbished, take it back to where you bought it from, when i worked at a local shop we got aftermarket alternators / stock alternators from advanced auto and they were refurbished and JUNK

Rocky

 

That is bad. Just for reference- a 20% underdrive crank will hit 14 volts at 850 rpm. Add an underdrive alt pulley to that and it hits 14 volts at 1000 rpm. This is on a stock alternator.

 

170 amp alt? where did u buy this from?

3Gs come in two flavors, 95A (small case) and 130A (large case). u can upgrade the large case to 200A but the stock 130A actually produces 160ish A at 2,000 rpm and 90A at idle (both mine did when i got them from the junkyard).

so i dont know where or who had this alt before u but it sounds fishy.

was it plug n play or did u need to adapt it to the harness?

 

stay away from online dating dano.

 

i was thinking the same thing......he may get a serial killer wife...

 

Uh dont go there.



You can always order from summit. they ship fast and free.. and you can
avoid taxes. If you are going to be in town let me know. We can do lunch
at applebees or something.

 

ive got a JM alternator and it does the same thing near the same thing that is..

stock i never had a problem i got a 170 ran bigger wires and all..you can hear my compressor die down at stop lights and stuff..system goin a/c on it poos..then idle up..i know it puts out more when drivin but the stock didnt die down this much.

how i fix that?

 

sounds like the wiring isnt compatible ala it isnt letting the exciter wire "kick" on the alt OR its not returning to the altenator somehow.

all the 3G swaps i have seen/done work flawlessly...

 

Evan, take it to an autozone or something and have it tested.

 

Small case 3G's have serious undercharging problems at idle when modified for high output.

Large case 3G's tend to produce enough amps at idle to keep things up. I had a 130 amp small 3G and it didn't do crap at idle. My replacement 200 amp large case 3G is an animal -- I love it.

It's a refurb, but I bought it used and paid very little for it. I have a spare regulator for it just in case, and my old 130 amp unit is in the toolbox as a spare. I can change one in about 15 minutes now, lol -- too much practice with changing alternators and pulleys.

I also got rid of my underdrive pulley, and put a smaller pulley on the alternator. This jacks up my idle charge quite a bit -- ideal for winching.

 

D. I found this.The moral of the story is High Amp alts are not very good at low rpms:

Pulley ratio is important to the performance of any alternator. Stock, low-amp alternators tend to have very flat performance curves because they are designed to provide output at slow speeds. High-amp alternators on the other hand tend to have very steep output curves, and as a result have relatively low output at slow speeds but ramp up very quickly. Symptoms of low idle output, such as dimming headlights, usually point to an underdrive problem.

The solution is swapping to either a larger crank pulley or a smaller alternator pulley. On the other end of the scale, Powermaster recommends limiting alternator speed to a maximum of 18,000 rpm. With a pulley ratio in the 3:1 range, you could easily exceed this speed in a drag car that frequently sees 6,000 rpm at the track. Here you would need to run either a smaller crank pulley or larger alternator pulley to reduce the alternator speed.

To calculate your engine’s pulley ratio, divide the diameter of the alternator pulley (A) by the diameter of the crankshaft pulley (B). For example, our Ramjet engine has a 6.750-inch crank pulley, so combined with the 2.625-inch pulley supplied with the alternator, it’s turning at 1,414 rpm at a 550-rpm engine idle. Powermaster rates its alternators idle output at a 2,400-rpm “alternator” idle, so this is considerably underdriven compared to the company’s recommendations, but since the rest of the system checked out OK, it’s fine as is.