Need Help With 3G Swap, Please!

[silvergt2001]

Hey guys I just did the swap, it ran fine for about 15 minutes, I then took it for a test drive and got on it really hard. The lights went dim, volt gauge dropped to nothing. I limped it home and found the alternator to read 21.5 volts at the hot post and the tester said bad diode. This is a brand new alternator.

I ran 4 gauge from the hot post on solenoid to the hot post on the alternator with a 200 amp breaker inline, this has since went bad/melted down. I did NOT run a 4 gauge ground.

DOES ANYONE HAVE IDEAS??? This is currently my DD please help guys..... THANKS!

 

[HISSIN50]

Did they give you a new alternator? If it was putting out over 20 volts, there isnt much that you can do.

Did it blow any light bulbs?

See how the new alternator does.

Good luck.

 

[04sleeper]

21.5 volts. I'm surprised your battery didn't explode.

I have seen many new alternators go bad, or not work right out of the box.

Read this for some useful info.
http://forums.stangnet.com/showthread.php?t=627646

 

[silvergt2001]

It was a new alternator, and everything went perfectly fine for about 15-20 minutes. After some "spirited" driving everything went dim and it stopped charging. It didn't hurt anything because I used the 200 amp breaker in between the alt and battery. It worked, but melted down in the process.

Could this be because I used my original smaller pulley from my stock alternator?? Thanks for the help everyone.

Oh btw, does the 4 gauge power cable go from alt to battery or alt to hot post on solenoid?? thanks

 

[Jaswir]

no pulley shouldnt of matter, i think it might of been the alternator...

 

[04sleeper]

Could this be because I used my original smaller pulley from my stock alternator?? Thanks for the help everyone.

Oh btw, does the 4 gauge power cable go from alt to battery or alt to hot post on solenoid?? thanks

If you have the stock crank pulley on then use the pulley it came with. If you have an underdrive crank pulley then use the smaller one.

Spinning the alternator too fast will kill it.

The 4 gauge power wire goes from the alt to hot post on the solenoid.

 

[jrichker]

As previously mentioned, the pulley size would not have caused this problem.

Three things:

1.) The battery or solenoid post are both suitable for attaching the power feed for the alternator. I used the solenoid because it made a neater installation in my car.

2.) The 4 gauge wire is only good for 160 amp at the temps found under the hood. Since the alternator was 130 amps, the preferred fuse should be 125-135 amps.

3.) The secondary power ground is between the back of the
intake manifold and the driver's side firewall. It is often missing or
loose. It supplies ground for the alternator, A/C compressor
clutch and other electrical accessories such as the gauges.
Any car that has a 3G or high output current alternator needs
a 4 gauge ground wire running from the block to the chassis
ground where the battery pigtail ground connects. The best
place for the block ground is where the battery ground for the
starter bolts down. The 3G has a 130 amp capacity, so you
wire the power side with 4 gauge wire. It stands to reason that the
ground side handles just a much current, so it needs to be 4
gauge too.

The chassis ground and battery pigtail ground go to the bolt being
pointed at in the following photo. The extra power ground for the alternator
should also bolt down there.

Picture courtesy timewarped1972

 

[dastang2]

it really does not matter where the 4 gauge wire goes as long as it is the hot post on battery or the solinoid. i prefer the battery as there are too many wires at the solinoid anyhow.

 

[HISSIN50]

Most 3G's dont like to see more than about 15,000 RPM. You can crunch the numbers if it helps.

Generally speaking, a 200 amp fuse was a little high for 4 AWG cable. I think I crunched the numbers for the length of cable I used and it was technically rated for 155 amps. That might be why your cable melted. You always fuse for the weakest item in the chain (alternator, cable, etc).

Like Kevin, I've gotten bad alts right out of the box. I would not have done anything but marched right down to the store and gotten a new unit. Have them bench test your brand new alternator before walkin out of the store.

Good luck.

 

[dec322]

Yeah, have the alt checked out. Also, on my 3g alt. there were warning telling me to make sure the battery is fully charged. If not, the alternator could die. I'm not sure about the details but maybe that is the case with yours.

 

[silvergt2001]

Hey everyone I just wanted to say thanks in helping me sort out this problem, as it has been resolved. It was a bad rebuilt alternator right out of the box. I took a warranty credit on that unit and bought a brand new one with no problems so far.

I changed the 200 amp breaker to a 150 buss breaker, but I have yet to put in the 4G ground wire from block to chassis. I will do this sometime this week.

Once again thanks to everyone who helped out. And as far as the swap is concerned, WOW! It feels like I'm driving my old 4.6 again with the non-dimming lights and quiet alternator.

 

[HISSIN50]

With everyones' great advice and your own smarts, it sounds like you got things whipped. Nice work!

Now turn on all the accessories and enjoy.