So I finished the swap and ran into virtually no issues until I scanned the car and it came back with p1637 generator L terminal. I receiving battery voltage at that L terminal on the back of the alternator which was around 14 something voltd...which seemed high. When the car is running I see 15.5 volts at the battery so it has a bit of an overcharging issue here.

Does this just sound like a bad alternator?

 

A quick bit of googling indicates that P1637 needs to be disabled in the PCM on a 24x-converted LT1. I’m not an expert here; hopefully somebody else knows more.

It’s normal for alternator voltage to vary depending on conditions. It should always be 13.0 or more when the engine is running, but I’ve seen north of 16v occasionally, and I don’t view yours as cause for concern.

I would generally expect it to settle once the engine has been running for a while, usually in the mid 13s to low 14s. If it stays high, there could be a problem. Best way to diagnose is to go back to AutoZone and ask for a charging system test. They’ll wheel a big machine out to the car and it will run a diagnostic test. A bad battery wouldn’t be a big surprise.

 

Today I saw 16.5 volts so I am guessing something is going on with this thing. I'll take it off and test it before I replace it.

 

Generally (not specific to the 24X conversion) you will see upwards of 16 volts right after you start the engine. The system is replacing the battery power drained cranking the engine. The voltage should gradually drop into the 13.0-13.5 volt range. If you see 16+ volts any other time, may be a problem with the regulator in the alternator.