I have a 1987 Camaro IROC convertible (LG4 - 305 carb) that's just got a 99 LS1/T56 (99 Trans Am WS6) dropped in. Car is up and running - everything looks good except for the battery isn't charging. I'm getting a P1637 code (generator L terminal circuit) which I can't clear. The harness is from Hawk's.

Any thoughts on chasing this down?

 

Is the alternator new or used?
Check the pins at both the alternator and PCM.
You should check the wire from the PCM to the alternator, meaning with the engine running is the value of the wire the same at the PCM as it is at the alternator. The PCM uses one single wire to command the alternator to turn on (atleast it is like that for 2001-02 wiring, depends what you are using)

 

Alternator is 'new'. The engine/trans was bought off eBay - alternator was indicated as replaced ~3000 miles ago.

Anyone know which pin to check on the PCM to compare voltage between it and the alt?

Bonus question: thinking of just running a 12v switched power with 1/2v 470 ohm resistor in place of the feed from PCM. My research so far suggests this is what guys with a carbed setup would do (this, or run the 'L' wire through a bulb upstream of alternator).

 

Terminal R15
http://www.ls2.com/boggs/torques/00pinpcm.htm
R15 will be at system voltage with engine running. The L-terminal will also be at system voltage if the alternator is charging. If the alternator did not turn on then the L-terminal will be a sink to ground. I'm guessing the fault code you're getting is because the engine PCM never sees the alternator turn on.

This isn't going to fix your problem if the alternator is broken. Just use the PCM since you have it.
470 Ohms is common tribal knowledge but 50 Ohm 10 Watt resistor is the correct value as told to me by the alternator application engineer at Delco Remy. The engineer suggested Radio Shack part number 271-133.

 

Thanks for this.
Fired it this am and took the RPM past 2500 and the charging circuit came to life. I thought I'd read somewhere that this might be necessary. Does that sound familiar to anyone else?

 

Sounds like there was a connection issue, then more current pushed through due to revving, and was enough to bridge the connection issue.

The wire at the alternator can be finiky. Mine had charging issues, and I ended up buying a new connector with pigtails from GM. It had 5 wires, and the gauge was heavier than the factory wire. So I deleted all by the one I needed, and spliced it further into the harness to get it away from header heat. That fixed all my problems. There was an intermittent short within the connector body itself.

Im not sure what hawks uses to build their harnesses. If they are re-worked factory, or all new. But it sure sounds like there was a connection issue.

Check all your grounds as well. I ran a dedicated ground from the alternator area over to the chassis. Also another at the rear of the motor. And beefed up the stock grounds. More grounds made everything work better. Stopped light dimming while idling, etc.

Keep your eye on it! It might drop back off if there's an actual issue. Never had to rev to get mine to charge, or any car really.

J.

 

Checked the exciter wire from PCM - had a nice ~5v. Still was charging intermittently - right up until the alternator blew last night.

New one going in today...

 

I guess thats a note to self. Out of all the things to go wrong, atleast it wasn't something worse and the problem showed itself soon enough. That's the one thing I love about Gen III systems, you don't have to beat around the bush very long, if there is a problem it will narrow it down for you. Even if the alternator did not "blow" it still told you where to look. According to the diagnosis tree if the pcm and the wire are good, it has to be the alternator. When I had charging issues with my TPI I virtually tore half the car apart. Problem turned out to be a broken connector at the starter no less and I already put an alternator on order before it showed itself. That basically did it for me with TPI electrical crap (I lost faith in it after it got me stuck in the dark 30 miles from home and stopped driving the car until a Gen 3 system takes its place)