Help understanding cts spark

6395 pcm with BHDF with 7.4 in 94 suburban with lightly modded 454.
there is a table CTS spark advance compensation vs vacuum vs temp.
that one seems straight forward as it adds a bit of spark when it is cold and takes away a bit of spark when it is hot. However it seems to be tied to the parameter coolant spark bias. It comes stock with a number of 20 in the selection. I have my total advance set to 41.8 and if you set the coolant spark bias to 0 it pegs the advance at 41.8, if you set it at 10 the advance runs about 36 and if you give it the least amount of gas it pegs the advance at 41.8. Can anyone shed light on that parameter. As a side note at light throttle the motor loves the high timing numbers.

you should look to see if the bias is included in the table's formula. if not, you have to subtract every value in the table to get the real value. depends who wrote the xdf. can you screenshot and post the formula for the table, or just post a copy of the xdf you're using?

I am using Advanced $OE TP5 v250.xdf and the formula is .351563*X. I just figured out how to make the parameter comments stay long enough to read them so I will try to figure out more on my own but any help would be great.

the bias setting shouldnt be adjusted its there so the coolant sensor based tables can have negative values

I have done some testing and am posting in case it might help someone. It looks like the rules gm used aren't the same for every application. I first started looking as my timing moved around more than I thought it should and the log numbers looked different than I thought they should.
I set most all the spark selection to 0 with the exception of cts spark bias which it seems to need and I suspect there is something in the overall formula that requires it and that formula is somewhere way beyond my pay grade. I set both spark tables to 20 everywhere. I got rid of any negative spark commands. I set the cts vs vacuum vs rpm table to all 00. My initial advance is at 4.9 in settings and it is also verified as base timing on balancer.
results were rock solid timing on the balancer of the commanded 20 degrees. The data stream showed a rock solid 15.1 degrees which I assume is the 20 minus the initial of 4.9 so the timing appears to end up as the amount you have commanded and the data log shows the amount it electronically take when added to the initial to get the total. This set of circumstances might very well only be valid for the 6395, I don't know.

How did you get the parameter comments to stay longer?....I'm getting sick of taking photos with my phone :-)

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Originally Posted by Kitch

How did you get the parameter comments to stay longer?....I'm getting sick of taking photos with my phone :-)

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You can get them to show up just like History tables or the Dash. Use View>Parameter Comments or F10.

Thanks, that was easy :-)