weird timing problem

[minytrker]

I tuned a camaro a4 with bolt on's and a small cam with heads a few weeks ago. The car drove perfect and ran really well and got a big increase in mileage. The car ran fine for about 500-800miles or so and then it started spark knocking real bad ( according to the owner) and he said it had no power unless you went wot. I finally got to scan it, it had no codes at all. I did however find what it was doing. Driving at part throttle the car is pulling all the timing back to min spark advance table values (B5915) I scan everything I could think of and could not find anything pulling timing. The only thing I could find is the fuel trims were -2 mostly and one cell had -11 for some reason. When the car was tuned it was drove 150 miles with the wide band in open and closed loop and the fuel was perfect.
I re-flashed the pcm with the exact same tune and it runs perfect again?

[SSpdDmon]

If the fuel trim cells aren't consistent throughout, you might get a lean knock. In other words, say you in FTC x and near the upper limits it wants to be -11%. But near the lower limits, it wants to be at -2%. Well, when you shift to a different portion of that cell, your fueling will be lean by 9% or roughly 15.9:1. I'm not saying fueling is the culprit here. But, it's a possibility.

One thing you could do is copy the high octane spark to the low and then watch for KR - especially in the cell that had -11% (if it's a normal driving cell and not idle/decel). Scanning it with the octane scaler forcing timing to the low octane table isn't going to help much if the lower table isn't a copy of the high octane table.

What mods does he have and were any changes made to his timing?

[minytrker]

The car had 0 kr ever. The car has headers, lid, 224 cam and a set of ls6 heads.

[wait4me]

burst knock is zeroed?

[minytrker]

burst knock is zeroed?

no, but im pretty sure i logged burst knock and saw none