LS3 480 HP crate engine alternator over voltage problems

[BigblockBob]

I purchased a GMPP LS3 480 hot cam crate engine from Summit in 2015. I just installed it in my 1969 Camaro (6 year build. Complete resto) and noticed right away that the voltage was creeping up to almost 19 volts and the alternator was getting hot to the touch in about 2-3 minutes after start up.

Here is what I am running:

1. GMPP LS3 480 hp engine
2. GM front drive assy with 145 amp 1 wire internally regulated alternator
3. GM engine harness (has been modified- shortened, repinned, etc.
4. American Autowire complete car wiring harness
5. Dakota Digital VHX gauges
6. Heavy grounds from engine to frame, firewall, etc.
7. 12 volt battery

I called GM Tech and they said they had a bad run of alternators around 2014 and 2015 and they were replacing them or having customers install a 50 ohm resistor inline on the wire into the alternator. Since my alt is over one year old they won't warranty it. I bought a 50 ohm 1 watt resistor and installed it but it did not help at all. I also called Summit and they won't warranty it either but will give me a 20% discount on a new one. I took the alt to the local Advance Auto and they said it checked out okay (though I'm not sure the guy knew exactly what he was doing). I'm sure that someone has run into this problem before but when I checked the forum I didn't see any other instances. Can anyone help or make any suggestions? Thanks!

[robs67camaro]

I have the same motor, and when I bought the front runner system from GM the alternator that came with the kit did the same thing you described,fortunately it was under warranty so I exchanged it and every thing is fine,i think your only option is to get a new alternator.

[dhutton]

I purchased a GMPP LS3 480 hot cam crate engine from Summit in 2015. I just installed it in my 1969 Camaro (6 year build. Complete resto) and noticed right away that the voltage was creeping up to almost 19 volts and the alternator was getting hot to the touch in about 2-3 minutes after start up.

Here is what I am running:

1. GMPP LS3 480 hp engine
2. GM front drive assy with 145 amp 1 wire internally regulated alternator
3. GM engine harness (has been modified- shortened, repinned, etc.
4. American Autowire complete car wiring harness
5. Dakota Digital VHX gauges
6. Heavy grounds from engine to frame, firewall, etc.
7. 12 volt battery

I called GM Tech and they said they had a bad run of alternators around 2014 and 2015 and they were replacing them or having customers install a 50 ohm resistor inline on the wire into the alternator. Since my alt is over one year old they won't warranty it. I bought a 50 ohm 1 watt resistor and installed it but it did not help at all. I also called Summit and they won't warranty it either but will give me a 20% discount on a new one. I took the alt to the local Advance Auto and they said it checked out okay (though I'm not sure the guy knew exactly what he was doing). I'm sure that someone has run into this problem before but when I checked the forum I didn't see any other instances. Can anyone help or make any suggestions? Thanks!

How did you connect the pigtail connector to the alternator? It sounds like you haven’t connected it correctly. Post a wiring drawing of how you connected it.

Don

[andrewb70]

The GMPP harness has an alternator connector on it. You may just have a bad alternator.

Andrew

[BigblockBob]

I have the same motor, and when I bought the front runner system from GM the alternator that came with the kit did the same thing you described,fortunately it was under warranty so I exchanged it and every thing is fine,i think your only option is to get a new alternator.


Thanks Rob. I did some searching on other forums and it seems that there were issues with alternators with bad voltage regs. Unfortunately for me I purchased the engine and front runner system in 2015 and just have gotten around to starting the engine this week. Unfortunately some projects take longer than the 1 year warranty they give you.

[BigblockBob]

Don, Thanks for your reply. The alt is a one wire connection and it looks like its most likely the voltage regulator. I will swap the alt to see if the problem goes away.

- - - Updated - - -

Thanks Andrew. You may be right. I'll swap to see if the problem goes away.

[dhutton]

Don, Thanks for your reply. The alt is a one wire connection and it looks like its most likely the voltage regulator. I will swap the alt to see if the problem goes away.

- - - Updated - - -

Thanks Andrew. You may be right. I'll swap to see if the problem goes away.

What did you connect that one wire to? The GMPP harness or something else?

Don

[BigblockBob]

What did you connect that one wire to? The GMPP harness or something else?

Don

So there is an orange wire that is the light wire used for the idiot light circuit. Since my application does not use an idiot light I needed some sort of resistor or an actual light bulb which provides resistance. I also had the 12 volt wire coming from the battery/starter solenoid.

I took the alternator into a shop and he simply changed out the regulator for a 12 volt stator activated set up. This seems to work well so far as I am not getting any over voltage.