Ignition Timing Retarding when AC on

I was trending my truck today on the way to a side job. I was trying to figure out whey my ignition was retarding almost like clock work, i noticed at the 8:45:45.652 mark that when i turn my AC system off that it stopped. Im new to tuning so was interested if y'all could take a look at it and tell me if there is something in the spark retard file that needs adjusted. I haven't changed anything in the tune except tire size, all other parameters are as found. I was told it was tuned but i couldn't tell you what has been changed.

Vehicle is as follows

2000 Chevrolet Silverado with LM7 5.3 Stock everything but intake tube tune.

The scan starts at 09:05:05.422. Post wrong one?

No its the correct trend. It starts at 805 am

Quote:

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Originally Posted by ShawnDaMan

No its the correct trend. It starts at 805 am

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This file was created in +6 CST, if you are in MD, you are one hour ahead so the time stamps will be off by an hour.

If it where off by exactly an hour I would say time zone? Here is what I see at 57m and 28sec into the file.
Attachment 106802

Created time is off exactly an hour, but there is no 09:45:45.652 like you have. Weird. Anyway, under the Spark/Advance tab, disable AC Bump TQ Spark and see if that makes a difference. It's probably stock for your tune, but the max retard under Torque Management/Engine then AC torque is very high. Before chasing those tables, disable the AC Bump TQ Spark and let's see if that makes a difference.

Thanks, i have made that change, i will update later when i get more data

So in the trends the knocking event which is causing the timing to retard is actually my AC compressor turning on. The old compressor is being picked up by the knock sensors as structure born noise and interpreted as a knock. I still have the original AC compressor on this 270K mile engine. ;). At any rate, the suggested change in settings did not achieve any results, i have changed that back, and have put in my books the need for a new AC compressor. Ill do that when it actually fails, and not as a preventative measure!