I use HPT. In my previous Fbodies, when I tuned timing, I focused on the high octane table since the car ran on premium and that was the first referenced table in the PCM.

On my truck, it came from the factory designed to run on 87. Does that mean the high octane spark table is for 87 octane or does the PCM reference the lo octane table first?

 

The pcm interpolates between high and low tables based on knock activity. If you have no knock you are running off of the high octane table.

 

Thats what I figured.

Thanks

 

There are a couple of different ways to tune it too. What I like to do is zero out all of the spark adders/subractors such as IAT, coolant temp, etc. and copy high octane to the low octane table so that no spark correction is happening. Then you can concentrate on one table only for actual tuning, then re-enable those other ones after tuning has been done on the main table (for safety sake).

 

You should also be able to log the knock learn factor in the scanner as well so you know which table the pcm is leaning towards.